linux-stable.git/net, branch v6.1.185

net: gro: properly validate BIG TCP aggregation criteria

2026-08-27T12:29:06+00:00

When GRO attempts to aggregate IPv6 packets beyond GRO_LEGACY_MAX_SIZE
(64KB), the aggregate should only be permitted for plain IPv6 TCP flows
that have sufficient MAC header room to insert the temporary HBH jumbo header.

In 6.1.y, skb_gro_receive() had two issues with this check:

1. It checked skb_headroom(p) instead of the actual space before the MAC
   header (p->mac_header). Because skb_headroom(p) measures (data - head),
   it includes mac_len. Crafted frames (e.g. injected via AF_PACKET) can
   pass the check with p->mac_header < 8 bytes. When ipv6_gro_complete()
   inserts the temporary HBH jumbo header, the memmove() starts before
   skb->head, causing an out-of-bounds write and wrapping skb->mac_header.
2. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark,
   which is 0 during receive, failing to reject encapsulated IPv6 flows
   (such as IP6IP6).

Fix skb_gro_receive() to strictly check:
- p->protocol == htons(ETH_P_IPV6)
- p->mac_header >= sizeof(struct hop_jumbo_hdr)
- ipv6_hdr(p)->nexthdr == IPPROTO_TCP
- Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation)

Returning -E2BIG from skb_gro_receive() ensures that packets which cannot
become BIG TCP are cleanly flushed at <= 64KB and delivered intact without
dropping.

This issue does not exist in mainline (7.0+) because the subsystem was
rewritten in commit 81be30c1f5f2 ("net/ipv6: Drop HBH for BIG TCP on RX
side"), making this fix relevant only for older stable branches like
6.18.y.

Fixes: 0fe79f28bfaf ("net: allow gro_max_size to exceed 65536")
Reported-by: Sam Dlinn 
Signed-off-by: Eric Dumazet 
Signed-off-by: Greg Kroah-Hartman

Bluetooth: hci_event: fix LE list UAF on reset

2026-08-27T12:29:06+00:00

commit 33af47e847fe4a28b109673affb5874015d54f5a upstream.

hci_cc_reset() clears the LE accept and resolving lists without taking
hdev->lock. Other command-complete handlers serialize updates to these
lists with that lock, and the debugfs readers hold it while walking them.

This permits the reset completion and a debugfs read to interleave as
follows:

  hci_rx_work                 debugfs reader
  -----------                 --------------
                              lock hdev->lock
                              fetch current entry
  list_del(entry)
  kfree(entry)
                              read entry fields

The reader then dereferences a freed list entry and may follow its stale
next pointer.

KASAN reported:

  BUG: KASAN: slab-use-after-free in white_list_show+0x15f/0x180
  Read of size 1 at addr ffff8881015dab16 by task poc/95

  Call Trace:
   white_list_show+0x15f/0x180
   seq_read_iter+0x3ff/0x1190
   seq_read+0x267/0x3d0
   vfs_read+0x177/0xa20
   ksys_read+0xf7/0x1c0

  Allocated by task 91:
   hci_bdaddr_list_add+0x1a6/0x3a0
   hci_cc_le_add_to_accept_list+0xab/0x140
   hci_cmd_complete_evt+0x26c/0x9a0
   hci_event_packet+0x454/0xb20
   hci_rx_work+0x293/0x730

  Freed by task 90:
   kfree+0x131/0x3c0
   hci_bdaddr_list_clear+0xd8/0x160
   hci_cc_reset+0x28a/0x370
   hci_cmd_complete_evt+0x26c/0x9a0
   hci_event_packet+0x454/0xb20
   hci_rx_work+0x293/0x730

Take hdev->lock around both list clears. This matches the existing
mutation and traversal locking convention.

Fixes: a4d5504d5c39 ("Bluetooth: Clear LE white list when resetting controller")
Fixes: cfdb0c2d095a ("Bluetooth: Store Resolv list size")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye 
Signed-off-by: Luiz Augusto von Dentz 
Signed-off-by: Greg Kroah-Hartman

can: isotp: fix timer drain order, wakeup handling and tx_gen ordering

2026-08-27T12:29:05+00:00

commit 050f010f920da17c1044a4f174766ad553e770b6 upstream.

This patch is a follow-up to commit cf070fe33bfb ("can: isotp: serialize
TX state transitions under so->rx_lock") which addresses following
sashiko-bot findings:

- isotp_sendmsg(): drain so->txfrtimer first so a stale callback can't
  re-arm echotimer after the claim

- isotp_release(): wake so->wait after forcing ISOTP_SHUTDOWN so a
  sleeping sendmsg() claim isn't stranded

- isotp_sendmsg(): have both wait_event_interruptible() calls in
  isotp_sendmsg() also wake on ISOTP_SHUTDOWN and do not return claim to
  IDLE to avoid corrupting a concurrent isotp_release() process.

- isotp_sendmsg(): handle potential claim of a new transfer when
  the wait_event_interruptible() call returns in CAN_ISOTP_WAIT_TX_DONE
  mode. Don't touch timers and states of the new transfer if a new thread
  incremented so->tx_gen before getting the lock at err_event_drop.

- isotp_sendmsg(): handle a stuck can_send() and omit timer and state
  changes if a new transfer was claimed. wait_tx_done() returns the error
  recorded in so->tx_result[], tagged with the caller's own generation.

- isotp_tx_timeout(): on a claimed timeout, record the ECOMM error for
  the timed-out transfer's own generation in so->tx_result[]; sk->sk_err
  is raised unconditionally, same as every other error path here.

- isotp_tx_gen_done()/isotp_tx_timeout(): always read tx.state (acquire)
  before tx_gen - the reverse order let a weakly ordered CPU pair a fresh
  tx.state with a stale tx_gen/tx_result slot.

- isotp_sendmsg(): wait_tx_done: drain sk_err via sock_error() once we
  have read the result from so->tx_result[], so an already-reported error
  doesn't stay latched for a later poll()/SO_ERROR.

Also align the remaining lock-free so->tx.state/rx.state/cfecho accesses
and use skb->hash as unique loopback echo frame indicator.

Fixes: cf070fe33bfb ("can: isotp: serialize TX state transitions under so->rx_lock")
Signed-off-by: Oliver Hartkopp 
Link: https://patch.msgid.link/20260724181525.43556-1-socketcan@hartkopp.net
Cc: stable@kernel.org
Signed-off-by: Marc Kleine-Budde 
Signed-off-by: Oliver Hartkopp 
Signed-off-by: Greg Kroah-Hartman

can: use skb hash instead of private variable in headroom

2026-08-27T12:29:05+00:00

commit d4fb6514ff8ed6912a71294e6b66a5d59ee88007 upstream.

The can_skb_priv::skbcnt variable is used to identify CAN skbs in the RX
path analogue to the skb->hash.

As the skb hash is not filled in CAN skbs move the private skbcnt value to
skb->hash and set skb->sw_hash accordingly. The skb->hash is a value used
for RPS to identify skbs. Use it as intended.

Signed-off-by: Marc Kleine-Budde 
Signed-off-by: Oliver Hartkopp 
Link: https://patch.msgid.link/20260201-can_skb_ext-v8-1-3635d790fe8b@hartkopp.net
Signed-off-by: Paolo Abeni 
Signed-off-by: Oliver Hartkopp 
Signed-off-by: Greg Kroah-Hartman

xfrm: fix sk_dst_cache double-free in xfrm_user_policy()

2026-08-27T12:29:05+00:00

[ Upstream commit c283e9ada7fcb7dd4b10592623086b2e6d2f9925 ]

xfrm_user_policy() clears the socket dst cache with __sk_dst_reset(),
i.e. the non-atomic __sk_dst_set(sk, NULL): it reads sk_dst_cache with
rcu_dereference_protected(), stores NULL and dst_release()s the old dst.
That is only safe if no other thread modifies sk_dst_cache concurrently.

For a connected UDP socket that does not hold: the transmit fast path
(udp_sendmsg -> sk_dst_check -> sk_dst_reset) resets the cache locklessly
with an atomic xchg(). A per-socket policy change racing a send can make
both sides observe the same old dst and each dst_release() it, dropping
the socket's single reference twice and freeing the xfrm_dst bundle while
it is still referenced:

  BUG: KASAN: slab-use-after-free in dst_release
  Write of size 4 at addr ffff88801897b6c0 by task exploit/155
  Call Trace:
   ...
   dst_release (... ./include/linux/rcuref.h:109)
   xfrm_user_policy (./include/net/sock.h:2239 ./include/net/sock.h:2256 net/xfrm/xfrm_state.c:3053)
   do_ip_setsockopt (net/ipv4/ip_sockglue.c:1347)
   ip_setsockopt (net/ipv4/ip_sockglue.c:1417)
   do_sock_setsockopt (net/socket.c:2368)
   __sys_setsockopt (net/socket.c:2393)
   __x64_sys_setsockopt (net/socket.c:2396)
   do_syscall_64 (arch/x86/entry/syscall_64.c:94)
   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)

Reachable by an unprivileged user via a user+network namespace.

Use the atomic sk_dst_reset() so the cache is cleared and released with a
single xchg(): whichever side wins releases the dst once, the other sees
NULL and does nothing. Behaviour is otherwise unchanged.

Fixes: 2b06cdf3e688 ("xfrm: Clear sk_dst_cache when applying per-socket policy.")
Fixes: be8f8284cd89 ("net: xfrm: allow clearing socket xfrm policies.")
Reported-by: AutonomousCodeSecurity@microsoft.com
Signed-off-by: Xiang Mei (Microsoft) 
Signed-off-by: Steffen Klassert 
Signed-off-by: Sasha Levin

mptcp: pm: fix data race in add_addr timer callback

2026-08-27T12:29:05+00:00

[ Upstream commit a7aad5b69d3bdaec20a3ed9284e184502450c0cd ]

The timer callback reads entry->retrans_times outside pm.lock to decide
whether to call mptcp_pm_subflow_established(). Since
mptcp_pm_announced_del_timer() can concurrently set retrans_times =
ADD_ADDR_RETRANS_MAX under pm.lock, a race condition exists.

I discovered this issue while studying the code. AI tools helped me to
verify the issue can potentially happen under race conditions.

Use a local 'retransmit' flag set inside pm.lock to capture whether
retransmission is still possible when the lock is taken. This allows to
call mptcp_pm_subflow_established() accordingly, and not depending on
the situation that can be different when checked outside the pm.lock.

Fixes: 348d5c1dec60 ("mptcp: move to next addr when timeout")
Cc: stable@vger.kernel.org
Signed-off-by: Qing Luo 
Reviewed-by: Matthieu Baerts (NGI0) 
Signed-off-by: Matthieu Baerts (NGI0) 
Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-4-b8f496d71664@kernel.org
Signed-off-by: Jakub Kicinski 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

mptcp: pm: ADD_ADDR rtx: free sk if last

2026-08-27T12:29:05+00:00

[ Upstream commit b7b9a461569734d33d3259d58d2507adfac107ed ]

When an ADD_ADDR is retransmitted, the sk is held in sk_reset_timer(),
and released at the end.

If at that moment, it was the last reference being held, the sk would
not be freed. sock_put() should then be called instead of __sock_put().

But that's not enough: if it is the last reference, sock_put() will call
sk_free(), which will end up calling sk_stop_timer_sync() on the same
timer, and waiting indefinitely to finish. So it is needed to mark that
the timer is done at the end of the timer handler when it has not been
rescheduled, not to call sk_stop_timer_sync() on "itself".

Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau 
Signed-off-by: Matthieu Baerts (NGI0) 
Link: https://patch.msgid.link/20260505-net-mptcp-pm-fixes-7-1-rc3-v1-5-fca8091060a4@kernel.org
Signed-off-by: Jakub Kicinski 
Stable-dep-of: a7aad5b69d3b ("mptcp: pm: fix data race in add_addr timer callback")
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

mptcp: pm: ADD_ADDR rtx: always decrease sk refcount

2026-08-27T12:29:05+00:00

[ Upstream commit 9634cb35af17019baec21ca648516ce376fa10e6 ]

When an ADD_ADDR is retransmitted, the sk is held in sk_reset_timer().
It should then be released in all cases at the end.

Some (unlikely) checks were returning directly instead of calling
sock_put() to decrease the refcount. Jump to a new 'exit' label to call
__sock_put() (which will become sock_put() in the next commit) to fix
this potential leak.

While at it, drop the '!msk' check which cannot happen because it is
never reset, and explicitly mark the remaining one as "unlikely".

Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau 
Signed-off-by: Matthieu Baerts (NGI0) 
Link: https://patch.msgid.link/20260505-net-mptcp-pm-fixes-7-1-rc3-v1-4-fca8091060a4@kernel.org
Signed-off-by: Jakub Kicinski 
Stable-dep-of: a7aad5b69d3b ("mptcp: pm: fix data race in add_addr timer callback")
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

ipv6: fix use-after-free in ip6_finish_output2()

2026-08-27T12:29:04+00:00

commit d0d48d999b0eee6bb176ef4e39d9be868fa80f7e upstream.

ip6_finish_output2() caches a pointer to the IPv6 destination
address (daddr) before invoking lwtunnel_xmit().  The LWT-BPF
transmit path or other encapsulation operations within
lwtunnel_xmit() can reallocate the skb head, freeing the memory
that daddr points to.  When lwtunnel_xmit() returns
LWTUNNEL_XMIT_CONTINUE, the function continues to use the stale
daddr pointer to compute the nexthop and to look up or create the
neighbour entry.  This results in a use-after-free read, which can
leak sensitive kernel data, pollute the neighbour table with
arbitrary values, misdirect traffic, or crash the system.

Fix this by re-fetching the IPv6 header and the destination
address pointer after lwtunnel_xmit() returns
LWTUNNEL_XMIT_CONTINUE, ensuring that the subsequent nexthop
computation and neighbour lookup operate on valid memory.

Fixes: e415ed3a4b8b ("ipv6: use skb_expand_head in ip6_finish_output2")
Cc: stable@vger.kernel.org
Reported-by: Vega 
Signed-off-by: Luxiao Xu 
Signed-off-by: Ren Wei 
Reviewed-by: Vadim Fedorenko 
Reviewed-by: Ido Schimmel 
Link: https://patch.msgid.link/4aa3f53bc44e79572c6dd2340ec7b68ef1a3d87d.1786516730.git.rakukuip@gmail.com
Signed-off-by: Jakub Kicinski 
Signed-off-by: Greg Kroah-Hartman

ipv4: reject undersized MTUs in ip_do_fragment()

2026-08-27T12:29:04+00:00

commit c0726f0caf8c6b3208552949e17d23634a2f3129 upstream.

ip_do_fragment() subtracts the IPv4 header length from the effective
MTU and passes the resulting payload MTU to ip_frag_next().

If the effective MTU is smaller than hlen + 8, ip_frag_next() rounds
the fragment payload length down to zero. The fragmentation state then
never makes forward progress: state->left, state->ptr and state->offset
stay unchanged while ip_do_fragment() keeps allocating and transmitting
header-only fragments until the softlockup detector fires.

This is reproducible with a route installed using "mtu lock 20", but it
is also reproducible without route MTU lock, for example by forwarding a
packet to a device whose MTU is 20.

Fix it in ip_do_fragment() by rejecting mtu < hlen + 8 with -EMSGSIZE,
matching the existing IPv6 fragmentation check.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Vega 
Signed-off-by: Yong Wang 
Signed-off-by: Ren Wei 
Reviewed-by: Ido Schimmel 
Link: https://patch.msgid.link/8809ef6314b98913681b0b370a05a85c2b6cd579.1786599079.git.edragain@163.com
Signed-off-by: Jakub Kicinski 
Signed-off-by: Greg Kroah-Hartman