linux-stable.git/net/ipv4/tcp_input.c, branch linux-4.19.y Linux kernel stable tree tcp: fix tcp_enter_recovery() to zero retrans_stamp when it's safe 2024-11-08T15:19:17+00:00 Neal Cardwell ncardwell@google.com 2024-10-01T20:05:16+00:00 a58878d7106b229a2d91a647629a0a7bedccaa8a [ Upstream commit b41b4cbd9655bcebcce941bef3601db8110335be ] Fix tcp_enter_recovery() so that if there are no retransmits out then we zero retrans_stamp when entering fast recovery. This is necessary to fix two buggy behaviors. Currently a non-zero retrans_stamp value can persist across multiple back-to-back loss recovery episodes. This is because we generally only clears retrans_stamp if we are completely done with loss recoveries, and get to tcp_try_to_open() and find !tcp_any_retrans_done(sk). This behavior causes two bugs: (1) When a loss recovery episode (CA_Loss or CA_Recovery) is followed immediately by a new CA_Recovery, the retrans_stamp value can persist and can be a time before this new CA_Recovery episode starts. That means that timestamp-based undo will be using the wrong retrans_stamp (a value that is too old) when comparing incoming TS ecr values to retrans_stamp to see if the current fast recovery episode can be undone. (2) If there is a roughly minutes-long sequence of back-to-back fast recovery episodes, one after another (e.g. in a shallow-buffered or policed bottleneck), where each fast recovery successfully makes forward progress and recovers one window of sequence space (but leaves at least one retransmit in flight at the end of the recovery), followed by several RTOs, then the ETIMEDOUT check may be using the wrong retrans_stamp (a value set at the start of the first fast recovery in the sequence). This can cause a very premature ETIMEDOUT, killing the connection prematurely. This commit changes the code to zero retrans_stamp when entering fast recovery, when this is known to be safe (no retransmits are out in the network). That ensures that when starting a fast recovery episode, and it is safe to do so, retrans_stamp is set when we send the fast retransmit packet. That addresses both bug (1) and bug (2) by ensuring that (if no retransmits are out when we start a fast recovery) we use the initial fast retransmit of this fast recovery as the time value for undo and ETIMEDOUT calculations. This makes intuitive sense, since the start of a new fast recovery episode (in a scenario where no lost packets are out in the network) means that the connection has made forward progress since the last RTO or fast recovery, and we should thus "restart the clock" used for both undo and ETIMEDOUT logic. Note that if when we start fast recovery there *are* retransmits out in the network, there can still be undesirable (1)/(2) issues. For example, after this patch we can still have the (1) and (2) problems in cases like this: + round 1: sender sends flight 1 + round 2: sender receives SACKs and enters fast recovery 1, retransmits some packets in flight 1 and then sends some new data as flight 2 + round 3: sender receives some SACKs for flight 2, notes losses, and retransmits some packets to fill the holes in flight 2 + fast recovery has some lost retransmits in flight 1 and continues for one or more rounds sending retransmits for flight 1 and flight 2 + fast recovery 1 completes when snd_una reaches high_seq at end of flight 1 + there are still holes in the SACK scoreboard in flight 2, so we enter fast recovery 2, but some retransmits in the flight 2 sequence range are still in flight (retrans_out > 0), so we can't execute the new retrans_stamp=0 added here to clear retrans_stamp It's not yet clear how to fix these remaining (1)/(2) issues in an efficient way without breaking undo behavior, given that retrans_stamp is currently used for undo and ETIMEDOUT. Perhaps the optimal (but expensive) strategy would be to set retrans_stamp to the timestamp of the earliest outstanding retransmit when entering fast recovery. But at least this commit makes things better. Note that this does not change the semantics of retrans_stamp; it simply makes retrans_stamp accurate in some cases where it was not before: (1) Some loss recovery, followed by an immediate entry into a fast recovery, where there are no retransmits out when entering the fast recovery. (2) When a TFO server has a SYNACK retransmit that sets retrans_stamp, and then the ACK that completes the 3-way handshake has SACK blocks that trigger a fast recovery. In this case when entering fast recovery we want to zero out the retrans_stamp from the TFO SYNACK retransmit, and set the retrans_stamp based on the timestamp of the fast recovery. We introduce a tcp_retrans_stamp_cleanup() helper, because this two-line sequence already appears in 3 places and is about to appear in 2 more as a result of this bug fix patch series. Once this bug fix patches series in the net branch makes it into the net-next branch we'll update the 3 other call sites to use the new helper. This is a long-standing issue. The Fixes tag below is chosen to be the oldest commit at which the patch will apply cleanly, which is from Linux v3.5 in 2012. Fixes: 1fbc340514fc ("tcp: early retransmit: tcp_enter_recovery()") Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20241001200517.2756803-3-ncardwell.sw@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit b41b4cbd9655bcebcce941bef3601db8110335be ]

Fix tcp_enter_recovery() so that if there are no retransmits out then
we zero retrans_stamp when entering fast recovery. This is necessary
to fix two buggy behaviors.

Currently a non-zero retrans_stamp value can persist across multiple
back-to-back loss recovery episodes. This is because we generally only
clears retrans_stamp if we are completely done with loss recoveries,
and get to tcp_try_to_open() and find !tcp_any_retrans_done(sk). This
behavior causes two bugs:

(1) When a loss recovery episode (CA_Loss or CA_Recovery) is followed
immediately by a new CA_Recovery, the retrans_stamp value can persist
and can be a time before this new CA_Recovery episode starts. That
means that timestamp-based undo will be using the wrong retrans_stamp
(a value that is too old) when comparing incoming TS ecr values to
retrans_stamp to see if the current fast recovery episode can be
undone.

(2) If there is a roughly minutes-long sequence of back-to-back fast
recovery episodes, one after another (e.g. in a shallow-buffered or
policed bottleneck), where each fast recovery successfully makes
forward progress and recovers one window of sequence space (but leaves
at least one retransmit in flight at the end of the recovery),
followed by several RTOs, then the ETIMEDOUT check may be using the
wrong retrans_stamp (a value set at the start of the first fast
recovery in the sequence). This can cause a very premature ETIMEDOUT,
killing the connection prematurely.

This commit changes the code to zero retrans_stamp when entering fast
recovery, when this is known to be safe (no retransmits are out in the
network). That ensures that when starting a fast recovery episode, and
it is safe to do so, retrans_stamp is set when we send the fast
retransmit packet. That addresses both bug (1) and bug (2) by ensuring
that (if no retransmits are out when we start a fast recovery) we use
the initial fast retransmit of this fast recovery as the time value
for undo and ETIMEDOUT calculations.

This makes intuitive sense, since the start of a new fast recovery
episode (in a scenario where no lost packets are out in the network)
means that the connection has made forward progress since the last RTO
or fast recovery, and we should thus "restart the clock" used for both
undo and ETIMEDOUT logic.

Note that if when we start fast recovery there *are* retransmits out
in the network, there can still be undesirable (1)/(2) issues. For
example, after this patch we can still have the (1) and (2) problems
in cases like this:

+ round 1: sender sends flight 1

+ round 2: sender receives SACKs and enters fast recovery 1,
  retransmits some packets in flight 1 and then sends some new data as
  flight 2

+ round 3: sender receives some SACKs for flight 2, notes losses, and
  retransmits some packets to fill the holes in flight 2

+ fast recovery has some lost retransmits in flight 1 and continues
  for one or more rounds sending retransmits for flight 1 and flight 2

+ fast recovery 1 completes when snd_una reaches high_seq at end of
  flight 1

+ there are still holes in the SACK scoreboard in flight 2, so we
  enter fast recovery 2, but some retransmits in the flight 2 sequence
  range are still in flight (retrans_out > 0), so we can't execute the
  new retrans_stamp=0 added here to clear retrans_stamp

It's not yet clear how to fix these remaining (1)/(2) issues in an
efficient way without breaking undo behavior, given that retrans_stamp
is currently used for undo and ETIMEDOUT. Perhaps the optimal (but
expensive) strategy would be to set retrans_stamp to the timestamp of
the earliest outstanding retransmit when entering fast recovery. But
at least this commit makes things better.

Note that this does not change the semantics of retrans_stamp; it
simply makes retrans_stamp accurate in some cases where it was not
before:

(1) Some loss recovery, followed by an immediate entry into a fast
recovery, where there are no retransmits out when entering the fast
recovery.

(2) When a TFO server has a SYNACK retransmit that sets retrans_stamp,
and then the ACK that completes the 3-way handshake has SACK blocks
that trigger a fast recovery. In this case when entering fast recovery
we want to zero out the retrans_stamp from the TFO SYNACK retransmit,
and set the retrans_stamp based on the timestamp of the fast recovery.

We introduce a tcp_retrans_stamp_cleanup() helper, because this
two-line sequence already appears in 3 places and is about to appear
in 2 more as a result of this bug fix patch series. Once this bug fix
patches series in the net branch makes it into the net-next branch
we'll update the 3 other call sites to use the new helper.

This is a long-standing issue. The Fixes tag below is chosen to be the
oldest commit at which the patch will apply cleanly, which is from
Linux v3.5 in 2012.

Fixes: 1fbc340514fc ("tcp: early retransmit: tcp_enter_recovery()")
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20241001200517.2756803-3-ncardwell.sw@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: introduce tcp_skb_timestamp_us() helper 2024-11-08T15:19:08+00:00 Eric Dumazet edumazet@google.com 2018-09-21T15:51:47+00:00 624db16292e1d6b0b54d911deca5a603e1dc8e1a [ Upstream commit 2fd66ffba50716fc5ab481c48db643af3bda2276 ] There are few places where TCP reads skb->skb_mstamp expecting a value in usec unit. skb->tstamp (aka skb->skb_mstamp) will soon store CLOCK_TAI nsec value. Add tcp_skb_timestamp_us() to provide proper conversion when needed. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Stable-dep-of: c8770db2d544 ("tcp: check skb is non-NULL in tcp_rto_delta_us()") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 2fd66ffba50716fc5ab481c48db643af3bda2276 ]

There are few places where TCP reads skb->skb_mstamp expecting
a value in usec unit.

skb->tstamp (aka skb->skb_mstamp) will soon store CLOCK_TAI nsec value.

Add tcp_skb_timestamp_us() to provide proper conversion when needed.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: c8770db2d544 ("tcp: check skb is non-NULL in tcp_rto_delta_us()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: fix incorrect undo caused by DSACK of TLP retransmit 2024-07-18T09:39:36+00:00 Neal Cardwell ncardwell@google.com 2024-07-03T17:12:46+00:00 83f5eb01c4beb9741bc1600bcd8b6e94a1774abe [ Upstream commit 0ec986ed7bab6801faed1440e8839dcc710331ff ] Loss recovery undo_retrans bookkeeping had a long-standing bug where a DSACK from a spurious TLP retransmit packet could cause an erroneous undo of a fast recovery or RTO recovery that repaired a single really-lost packet (in a sequence range outside that of the TLP retransmit). Basically, because the loss recovery state machine didn't account for the fact that it sent a TLP retransmit, the DSACK for the TLP retransmit could erroneously be implicitly be interpreted as corresponding to the normal fast recovery or RTO recovery retransmit that plugged a real hole, thus resulting in an improper undo. For example, consider the following buggy scenario where there is a real packet loss but the congestion control response is improperly undone because of this bug: + send packets P1, P2, P3, P4 + P1 is really lost + send TLP retransmit of P4 + receive SACK for original P2, P3, P4 + enter fast recovery, fast-retransmit P1, increment undo_retrans to 1 + receive DSACK for TLP P4, decrement undo_retrans to 0, undo (bug!) + receive cumulative ACK for P1-P4 (fast retransmit plugged real hole) The fix: when we initialize undo machinery in tcp_init_undo(), if there is a TLP retransmit in flight, then increment tp->undo_retrans so that we make sure that we receive a DSACK corresponding to the TLP retransmit, as well as DSACKs for all later normal retransmits, before triggering a loss recovery undo. Note that we also have to move the line that clears tp->tlp_high_seq for RTO recovery, so that upon RTO we remember the tp->tlp_high_seq value until tcp_init_undo() and clear it only afterward. Also note that the bug dates back to the original 2013 TLP implementation, commit 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)"). However, this patch will only compile and work correctly with kernels that have tp->tlp_retrans, which was added only in v5.8 in 2020 in commit 76be93fc0702 ("tcp: allow at most one TLP probe per flight"). So we associate this fix with that later commit. Fixes: 76be93fc0702 ("tcp: allow at most one TLP probe per flight") Signed-off-by: Neal Cardwell <ncardwell@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Kevin Yang <yyd@google.com> Link: https://patch.msgid.link/20240703171246.1739561-1-ncardwell.sw@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 0ec986ed7bab6801faed1440e8839dcc710331ff ]

Loss recovery undo_retrans bookkeeping had a long-standing bug where a
DSACK from a spurious TLP retransmit packet could cause an erroneous
undo of a fast recovery or RTO recovery that repaired a single
really-lost packet (in a sequence range outside that of the TLP
retransmit). Basically, because the loss recovery state machine didn't
account for the fact that it sent a TLP retransmit, the DSACK for the
TLP retransmit could erroneously be implicitly be interpreted as
corresponding to the normal fast recovery or RTO recovery retransmit
that plugged a real hole, thus resulting in an improper undo.

For example, consider the following buggy scenario where there is a
real packet loss but the congestion control response is improperly
undone because of this bug:

+ send packets P1, P2, P3, P4
+ P1 is really lost
+ send TLP retransmit of P4
+ receive SACK for original P2, P3, P4
+ enter fast recovery, fast-retransmit P1, increment undo_retrans to 1
+ receive DSACK for TLP P4, decrement undo_retrans to 0, undo (bug!)
+ receive cumulative ACK for P1-P4 (fast retransmit plugged real hole)

The fix: when we initialize undo machinery in tcp_init_undo(), if
there is a TLP retransmit in flight, then increment tp->undo_retrans
so that we make sure that we receive a DSACK corresponding to the TLP
retransmit, as well as DSACKs for all later normal retransmits, before
triggering a loss recovery undo. Note that we also have to move the
line that clears tp->tlp_high_seq for RTO recovery, so that upon RTO
we remember the tp->tlp_high_seq value until tcp_init_undo() and clear
it only afterward.

Also note that the bug dates back to the original 2013 TLP
implementation, commit 6ba8a3b19e76 ("tcp: Tail loss probe (TLP)").

However, this patch will only compile and work correctly with kernels
that have tp->tlp_retrans, which was added only in v5.8 in 2020 in
commit 76be93fc0702 ("tcp: allow at most one TLP probe per flight").
So we associate this fix with that later commit.

Fixes: 76be93fc0702 ("tcp: allow at most one TLP probe per flight")
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Kevin Yang <yyd@google.com>
Link: https://patch.msgid.link/20240703171246.1739561-1-ncardwell.sw@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open() 2024-07-18T09:39:34+00:00 Neal Cardwell ncardwell@google.com 2024-06-27T02:42:27+00:00 8b5fd51b3040ce2596d22a72767c66d7435853b6 [ Upstream commit a6458ab7fd4f427d4f6f54380453ad255b7fde83 ] In some production workloads we noticed that connections could sometimes close extremely prematurely with ETIMEDOUT after transmitting only 1 TLP and RTO retransmission (when we would normally expect roughly tcp_retries2 = TCP_RETR2 = 15 RTOs before a connection closes with ETIMEDOUT). From tracing we determined that these workloads can suffer from a scenario where in fast recovery, after some retransmits, a DSACK undo can happen at a point where the scoreboard is totally clear (we have retrans_out == sacked_out == lost_out == 0). In such cases, calling tcp_try_keep_open() means that we do not execute any code path that clears tp->retrans_stamp to 0. That means that tp->retrans_stamp can remain erroneously set to the start time of the undone fast recovery, even after the fast recovery is undone. If minutes or hours elapse, and then a TLP/RTO/RTO sequence occurs, then the start_ts value in retransmits_timed_out() (which is from tp->retrans_stamp) will be erroneously ancient (left over from the fast recovery undone via DSACKs). Thus this ancient tp->retrans_stamp value can cause the connection to die very prematurely with ETIMEDOUT via tcp_write_err(). The fix: we change DSACK undo in fast recovery (TCP_CA_Recovery) to call tcp_try_to_open() instead of tcp_try_keep_open(). This ensures that if no retransmits are in flight at the time of DSACK undo in fast recovery then we properly zero retrans_stamp. Note that calling tcp_try_to_open() is more consistent with other loss recovery behavior, since normal fast recovery (CA_Recovery) and RTO recovery (CA_Loss) both normally end when tp->snd_una meets or exceeds tp->high_seq and then in tcp_fastretrans_alert() the "default" switch case executes tcp_try_to_open(). Also note that by inspection this change to call tcp_try_to_open() implies at least one other nice bug fix, where now an ECE-marked DSACK that causes an undo will properly invoke tcp_enter_cwr() rather than ignoring the ECE mark. Fixes: c7d9d6a185a7 ("tcp: undo on DSACK during recovery") Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit a6458ab7fd4f427d4f6f54380453ad255b7fde83 ]

In some production workloads we noticed that connections could
sometimes close extremely prematurely with ETIMEDOUT after
transmitting only 1 TLP and RTO retransmission (when we would normally
expect roughly tcp_retries2 = TCP_RETR2 = 15 RTOs before a connection
closes with ETIMEDOUT).

From tracing we determined that these workloads can suffer from a
scenario where in fast recovery, after some retransmits, a DSACK undo
can happen at a point where the scoreboard is totally clear (we have
retrans_out == sacked_out == lost_out == 0). In such cases, calling
tcp_try_keep_open() means that we do not execute any code path that
clears tp->retrans_stamp to 0. That means that tp->retrans_stamp can
remain erroneously set to the start time of the undone fast recovery,
even after the fast recovery is undone. If minutes or hours elapse,
and then a TLP/RTO/RTO sequence occurs, then the start_ts value in
retransmits_timed_out() (which is from tp->retrans_stamp) will be
erroneously ancient (left over from the fast recovery undone via
DSACKs). Thus this ancient tp->retrans_stamp value can cause the
connection to die very prematurely with ETIMEDOUT via
tcp_write_err().

The fix: we change DSACK undo in fast recovery (TCP_CA_Recovery) to
call tcp_try_to_open() instead of tcp_try_keep_open(). This ensures
that if no retransmits are in flight at the time of DSACK undo in fast
recovery then we properly zero retrans_stamp. Note that calling
tcp_try_to_open() is more consistent with other loss recovery
behavior, since normal fast recovery (CA_Recovery) and RTO recovery
(CA_Loss) both normally end when tp->snd_una meets or exceeds
tp->high_seq and then in tcp_fastretrans_alert() the "default" switch
case executes tcp_try_to_open(). Also note that by inspection this
change to call tcp_try_to_open() implies at least one other nice bug
fix, where now an ECE-marked DSACK that causes an undo will properly
invoke tcp_enter_cwr() rather than ignoring the ECE mark.

Fixes: c7d9d6a185a7 ("tcp: undo on DSACK during recovery")
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
net: tcp better handling of reordering then loss cases 2024-07-18T09:39:34+00:00 Yuchung Cheng ycheng@google.com 2021-06-03T00:51:21+00:00 550968385e2f0df8e29c6431ab2dc0961499acb0 [ Upstream commit a29cb6914681a55667436a9eb7a42e28da8cf387 ] This patch aims to improve the situation when reordering and loss are ocurring in the same flight of packets. Previously the reordering would first induce a spurious recovery, then the subsequent ACK may undo the cwnd (based on the timestamps e.g.). However the current loss recovery does not proceed to invoke RACK to install a reordering timer. If some packets are also lost, this may lead to a long RTO-based recovery. An example is https://groups.google.com/g/bbr-dev/c/OFHADvJbTEI The solution is to after reverting the recovery, always invoke RACK to either mount the RACK timer to fast retransmit after the reordering window, or restarts the recovery if new loss is identified. Hence it is possible the sender may go from Recovery to Disorder/Open to Recovery again in one ACK. Reported-by: mingkun bian <bianmingkun@gmail.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit a29cb6914681a55667436a9eb7a42e28da8cf387 ]

This patch aims to improve the situation when reordering and loss are
ocurring in the same flight of packets.

Previously the reordering would first induce a spurious recovery, then
the subsequent ACK may undo the cwnd (based on the timestamps e.g.).
However the current loss recovery does not proceed to invoke
RACK to install a reordering timer. If some packets are also lost, this
may lead to a long RTO-based recovery. An example is
https://groups.google.com/g/bbr-dev/c/OFHADvJbTEI

The solution is to after reverting the recovery, always invoke RACK
to either mount the RACK timer to fast retransmit after the reordering
window, or restarts the recovery if new loss is identified. Hence
it is possible the sender may go from Recovery to Disorder/Open to
Recovery again in one ACK.

Reported-by: mingkun bian <bianmingkun@gmail.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: add ece_ack flag to reno sack functions 2024-07-18T09:39:34+00:00 Yousuk Seung ysseung@google.com 2020-06-27T04:05:33+00:00 57a672a35020884512ae64fbbcb5c70149424781 [ Upstream commit c634e34f6ebfb75259e6ce467523fd3adf30d3d2 ] Pass a boolean flag that tells the ECE state of the current ack to reno sack functions. This is pure refactor for future patches to improve tracking delivered counts. Signed-off-by: Yousuk Seung <ysseung@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit c634e34f6ebfb75259e6ce467523fd3adf30d3d2 ]

Pass a boolean flag that tells the ECE state of the current ack to reno
sack functions. This is pure refactor for future patches to improve
tracking delivered counts.

Signed-off-by: Yousuk Seung <ysseung@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: tcp_mark_head_lost is only valid for sack-tcp 2024-07-18T09:39:34+00:00 zhang kai zhangkaiheb@126.com 2020-05-07T03:08:30+00:00 552970cb728120695820ef9decb0933b3f9ce774 [ Upstream commit 636ef28d6e4d174e424102466caf572b0406fb0e ] so tcp_is_sack/reno checks are removed from tcp_mark_head_lost. Signed-off-by: zhang kai <zhangkaiheb@126.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 636ef28d6e4d174e424102466caf572b0406fb0e ]

so tcp_is_sack/reno checks are removed from tcp_mark_head_lost.

Signed-off-by: zhang kai <zhangkaiheb@126.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: take care of compressed acks in tcp_add_reno_sack() 2024-07-18T09:39:33+00:00 Eric Dumazet edumazet@google.com 2018-11-27T22:42:01+00:00 0cb018bf9217805f97740fe83261e18199fc2773 [ Upstream commit 19119f298bb1f2af3bb1093f5f2a1fed8da94e37 ] Neal pointed out that non sack flows might suffer from ACK compression added in the following patch ("tcp: implement coalescing on backlog queue") Instead of tweaking tcp_add_backlog() we can take into account how many ACK were coalesced, this information will be available in skb_shinfo(skb)->gso_segs Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 19119f298bb1f2af3bb1093f5f2a1fed8da94e37 ]

Neal pointed out that non sack flows might suffer from ACK compression
added in the following patch ("tcp: implement coalescing on backlog queue")

Instead of tweaking tcp_add_backlog() we can take into
account how many ACK were coalesced, this information
will be available in skb_shinfo(skb)->gso_segs

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: a6458ab7fd4f ("UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: defer shutdown(SEND_SHUTDOWN) for TCP_SYN_RECV sockets 2024-05-17T09:42:41+00:00 Eric Dumazet edumazet@google.com 2024-05-01T12:54:48+00:00 34e41a031fd7523bf1cd00a2adca2370aebea270 [ Upstream commit 94062790aedb505bdda209b10bea47b294d6394f ] TCP_SYN_RECV state is really special, it is only used by cross-syn connections, mostly used by fuzzers. In the following crash [1], syzbot managed to trigger a divide by zero in tcp_rcv_space_adjust() A socket makes the following state transitions, without ever calling tcp_init_transfer(), meaning tcp_init_buffer_space() is also not called. TCP_CLOSE connect() TCP_SYN_SENT TCP_SYN_RECV shutdown() -> tcp_shutdown(sk, SEND_SHUTDOWN) TCP_FIN_WAIT1 To fix this issue, change tcp_shutdown() to not perform a TCP_SYN_RECV -> TCP_FIN_WAIT1 transition, which makes no sense anyway. When tcp_rcv_state_process() later changes socket state from TCP_SYN_RECV to TCP_ESTABLISH, then look at sk->sk_shutdown to finally enter TCP_FIN_WAIT1 state, and send a FIN packet from a sane socket state. This means tcp_send_fin() can now be called from BH context, and must use GFP_ATOMIC allocations. [1] divide error: 0000 [#1] PREEMPT SMP KASAN NOPTI CPU: 1 PID: 5084 Comm: syz-executor358 Not tainted 6.9.0-rc6-syzkaller-00022-g98369dccd2f8 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024 RIP: 0010:tcp_rcv_space_adjust+0x2df/0x890 net/ipv4/tcp_input.c:767 Code: e3 04 4c 01 eb 48 8b 44 24 38 0f b6 04 10 84 c0 49 89 d5 0f 85 a5 03 00 00 41 8b 8e c8 09 00 00 89 e8 29 c8 48 0f af c3 31 d2 <48> f7 f1 48 8d 1c 43 49 8d 96 76 08 00 00 48 89 d0 48 c1 e8 03 48 RSP: 0018:ffffc900031ef3f0 EFLAGS: 00010246 RAX: 0c677a10441f8f42 RBX: 000000004fb95e7e RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000027d4b11f R08: ffffffff89e535a4 R09: 1ffffffff25e6ab7 R10: dffffc0000000000 R11: ffffffff8135e920 R12: ffff88802a9f8d30 R13: dffffc0000000000 R14: ffff88802a9f8d00 R15: 1ffff1100553f2da FS: 00005555775c0380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f1155bf2304 CR3: 000000002b9f2000 CR4: 0000000000350ef0 Call Trace: <TASK> tcp_recvmsg_locked+0x106d/0x25a0 net/ipv4/tcp.c:2513 tcp_recvmsg+0x25d/0x920 net/ipv4/tcp.c:2578 inet6_recvmsg+0x16a/0x730 net/ipv6/af_inet6.c:680 sock_recvmsg_nosec net/socket.c:1046 [inline] sock_recvmsg+0x109/0x280 net/socket.c:1068 ____sys_recvmsg+0x1db/0x470 net/socket.c:2803 ___sys_recvmsg net/socket.c:2845 [inline] do_recvmmsg+0x474/0xae0 net/socket.c:2939 __sys_recvmmsg net/socket.c:3018 [inline] __do_sys_recvmmsg net/socket.c:3041 [inline] __se_sys_recvmmsg net/socket.c:3034 [inline] __x64_sys_recvmmsg+0x199/0x250 net/socket.c:3034 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7faeb6363db9 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffcc1997168 EFLAGS: 00000246 ORIG_RAX: 000000000000012b RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007faeb6363db9 RDX: 0000000000000001 RSI: 0000000020000bc0 RDI: 0000000000000005 RBP: 0000000000000000 R08: 0000000000000000 R09: 000000000000001c R10: 0000000000000122 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000001 Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Link: https://lore.kernel.org/r/20240501125448.896529-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 94062790aedb505bdda209b10bea47b294d6394f ]

TCP_SYN_RECV state is really special, it is only used by
cross-syn connections, mostly used by fuzzers.

In the following crash [1], syzbot managed to trigger a divide
by zero in tcp_rcv_space_adjust()

A socket makes the following state transitions,
without ever calling tcp_init_transfer(),
meaning tcp_init_buffer_space() is also not called.

         TCP_CLOSE
connect()
         TCP_SYN_SENT
         TCP_SYN_RECV
shutdown() -> tcp_shutdown(sk, SEND_SHUTDOWN)
         TCP_FIN_WAIT1

To fix this issue, change tcp_shutdown() to not
perform a TCP_SYN_RECV -> TCP_FIN_WAIT1 transition,
which makes no sense anyway.

When tcp_rcv_state_process() later changes socket state
from TCP_SYN_RECV to TCP_ESTABLISH, then look at
sk->sk_shutdown to finally enter TCP_FIN_WAIT1 state,
and send a FIN packet from a sane socket state.

This means tcp_send_fin() can now be called from BH
context, and must use GFP_ATOMIC allocations.

[1]
divide error: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 1 PID: 5084 Comm: syz-executor358 Not tainted 6.9.0-rc6-syzkaller-00022-g98369dccd2f8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
 RIP: 0010:tcp_rcv_space_adjust+0x2df/0x890 net/ipv4/tcp_input.c:767
Code: e3 04 4c 01 eb 48 8b 44 24 38 0f b6 04 10 84 c0 49 89 d5 0f 85 a5 03 00 00 41 8b 8e c8 09 00 00 89 e8 29 c8 48 0f af c3 31 d2 <48> f7 f1 48 8d 1c 43 49 8d 96 76 08 00 00 48 89 d0 48 c1 e8 03 48
RSP: 0018:ffffc900031ef3f0 EFLAGS: 00010246
RAX: 0c677a10441f8f42 RBX: 000000004fb95e7e RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000027d4b11f R08: ffffffff89e535a4 R09: 1ffffffff25e6ab7
R10: dffffc0000000000 R11: ffffffff8135e920 R12: ffff88802a9f8d30
R13: dffffc0000000000 R14: ffff88802a9f8d00 R15: 1ffff1100553f2da
FS:  00005555775c0380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1155bf2304 CR3: 000000002b9f2000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
  tcp_recvmsg_locked+0x106d/0x25a0 net/ipv4/tcp.c:2513
  tcp_recvmsg+0x25d/0x920 net/ipv4/tcp.c:2578
  inet6_recvmsg+0x16a/0x730 net/ipv6/af_inet6.c:680
  sock_recvmsg_nosec net/socket.c:1046 [inline]
  sock_recvmsg+0x109/0x280 net/socket.c:1068
  ____sys_recvmsg+0x1db/0x470 net/socket.c:2803
  ___sys_recvmsg net/socket.c:2845 [inline]
  do_recvmmsg+0x474/0xae0 net/socket.c:2939
  __sys_recvmmsg net/socket.c:3018 [inline]
  __do_sys_recvmmsg net/socket.c:3041 [inline]
  __se_sys_recvmmsg net/socket.c:3034 [inline]
  __x64_sys_recvmmsg+0x199/0x250 net/socket.c:3034
  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
  do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7faeb6363db9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffcc1997168 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007faeb6363db9
RDX: 0000000000000001 RSI: 0000000020000bc0 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: 000000000000001c
R10: 0000000000000122 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000001

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Link: https://lore.kernel.org/r/20240501125448.896529-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: do not accept ACK of bytes we never sent 2023-12-13T16:42:17+00:00 Eric Dumazet edumazet@google.com 2023-12-05T16:18:41+00:00 458f07ffeccd17f99942311e09ef574ddf4a414a [ Upstream commit 3d501dd326fb1c73f1b8206d4c6e1d7b15c07e27 ] This patch is based on a detailed report and ideas from Yepeng Pan and Christian Rossow. ACK seq validation is currently following RFC 5961 5.2 guidelines: The ACK value is considered acceptable only if it is in the range of ((SND.UNA - MAX.SND.WND) <= SEG.ACK <= SND.NXT). All incoming segments whose ACK value doesn't satisfy the above condition MUST be discarded and an ACK sent back. It needs to be noted that RFC 793 on page 72 (fifth check) says: "If the ACK is a duplicate (SEG.ACK < SND.UNA), it can be ignored. If the ACK acknowledges something not yet sent (SEG.ACK > SND.NXT) then send an ACK, drop the segment, and return". The "ignored" above implies that the processing of the incoming data segment continues, which means the ACK value is treated as acceptable. This mitigation makes the ACK check more stringent since any ACK < SND.UNA wouldn't be accepted, instead only ACKs that are in the range ((SND.UNA - MAX.SND.WND) <= SEG.ACK <= SND.NXT) get through. This can be refined for new (and possibly spoofed) flows, by not accepting ACK for bytes that were never sent. This greatly improves TCP security at a little cost. I added a Fixes: tag to make sure this patch will reach stable trees, even if the 'blamed' patch was adhering to the RFC. tp->bytes_acked was added in linux-4.2 Following packetdrill test (courtesy of Yepeng Pan) shows the issue at hand: 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1024) = 0 // ---------------- Handshake ------------------- // // when window scale is set to 14 the window size can be extended to // 65535 * (2^14) = 1073725440. Linux would accept an ACK packet // with ack number in (Server_ISN+1-1073725440. Server_ISN+1) // ,though this ack number acknowledges some data never // sent by the server. +0 < S 0:0(0) win 65535 <mss 1400,nop,wscale 14> +0 > S. 0:0(0) ack 1 <...> +0 < . 1:1(0) ack 1 win 65535 +0 accept(3, ..., ...) = 4 // For the established connection, we send an ACK packet, // the ack packet uses ack number 1 - 1073725300 + 2^32, // where 2^32 is used to wrap around. // Note: we used 1073725300 instead of 1073725440 to avoid possible // edge cases. // 1 - 1073725300 + 2^32 = 3221241997 // Oops, old kernels happily accept this packet. +0 < . 1:1001(1000) ack 3221241997 win 65535 // After the kernel fix the following will be replaced by a challenge ACK, // and prior malicious frame would be dropped. +0 > . 1:1(0) ack 1001 Fixes: 354e4aa391ed ("tcp: RFC 5961 5.2 Blind Data Injection Attack Mitigation") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Yepeng Pan <yepeng.pan@cispa.de> Reported-by: Christian Rossow <rossow@cispa.de> Acked-by: Neal Cardwell <ncardwell@google.com> Link: https://lore.kernel.org/r/20231205161841.2702925-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 3d501dd326fb1c73f1b8206d4c6e1d7b15c07e27 ]

This patch is based on a detailed report and ideas from Yepeng Pan
and Christian Rossow.

ACK seq validation is currently following RFC 5961 5.2 guidelines:

   The ACK value is considered acceptable only if
   it is in the range of ((SND.UNA - MAX.SND.WND) <= SEG.ACK <=
   SND.NXT).  All incoming segments whose ACK value doesn't satisfy the
   above condition MUST be discarded and an ACK sent back.  It needs to
   be noted that RFC 793 on page 72 (fifth check) says: "If the ACK is a
   duplicate (SEG.ACK < SND.UNA), it can be ignored.  If the ACK
   acknowledges something not yet sent (SEG.ACK > SND.NXT) then send an
   ACK, drop the segment, and return".  The "ignored" above implies that
   the processing of the incoming data segment continues, which means
   the ACK value is treated as acceptable.  This mitigation makes the
   ACK check more stringent since any ACK < SND.UNA wouldn't be
   accepted, instead only ACKs that are in the range ((SND.UNA -
   MAX.SND.WND) <= SEG.ACK <= SND.NXT) get through.

This can be refined for new (and possibly spoofed) flows,
by not accepting ACK for bytes that were never sent.

This greatly improves TCP security at a little cost.

I added a Fixes: tag to make sure this patch will reach stable trees,
even if the 'blamed' patch was adhering to the RFC.

tp->bytes_acked was added in linux-4.2

Following packetdrill test (courtesy of Yepeng Pan) shows
the issue at hand:

0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+0 bind(3, ..., ...) = 0
+0 listen(3, 1024) = 0

// ---------------- Handshake ------------------- //

// when window scale is set to 14 the window size can be extended to
// 65535 * (2^14) = 1073725440. Linux would accept an ACK packet
// with ack number in (Server_ISN+1-1073725440. Server_ISN+1)
// ,though this ack number acknowledges some data never
// sent by the server.

+0 < S 0:0(0) win 65535 <mss 1400,nop,wscale 14>
+0 > S. 0:0(0) ack 1 <...>
+0 < . 1:1(0) ack 1 win 65535
+0 accept(3, ..., ...) = 4

// For the established connection, we send an ACK packet,
// the ack packet uses ack number 1 - 1073725300 + 2^32,
// where 2^32 is used to wrap around.
// Note: we used 1073725300 instead of 1073725440 to avoid possible
// edge cases.
// 1 - 1073725300 + 2^32 = 3221241997

// Oops, old kernels happily accept this packet.
+0 < . 1:1001(1000) ack 3221241997 win 65535

// After the kernel fix the following will be replaced by a challenge ACK,
// and prior malicious frame would be dropped.
+0 > . 1:1(0) ack 1001

Fixes: 354e4aa391ed ("tcp: RFC 5961 5.2 Blind Data Injection Attack Mitigation")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Yepeng Pan <yepeng.pan@cispa.de>
Reported-by: Christian Rossow <rossow@cispa.de>
Acked-by: Neal Cardwell <ncardwell@google.com>
Link: https://lore.kernel.org/r/20231205161841.2702925-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>