Some TCP peers announce a very small MSS option in their SYN and/or
SYN/ACK messages.

This forces the stack to send packets with a very high network/cpu
overhead.

Linux has enforced a minimal value of 48. Since this value includes
the size of TCP options, and that the options can consume up to 40
bytes, this means that each segment can include only 8 bytes of payload.

In some cases, it can be useful to increase the minimal value
to a saner value.

We still let the default to 48 (TCP_MIN_SND_MSS), for compatibility
reasons.

Note that TCP_MAXSEG socket option enforces a minimal value
of (TCP_MIN_MSS). David Miller increased this minimal value
in commit c39508d6f118 ("tcp: Make TCP_MAXSEG minimum more correct.")
from 64 to 88.

We might in the future merge TCP_MIN_SND_MSS and TCP_MIN_MSS.

CVE-2019-11479 -- tcp mss hardcoded to 48

Signed-off-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Jonathan Looney <jtl@netflix.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Bruce Curtis <brucec@netflix.com>
Cc: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Instead of relying on rps_needed, it is safer to use a separate
static key, since we do not want to enable TCP rx_skb_cache
by default. This feature can cause huge increase of memory
usage on hosts with millions of sockets.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This patch fixes some spelling typos found in ip-sysctl.txt

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Three trivial overlapping conflicts.

Signed-off-by: David S. Miller <davem@davemloft.net>

Steffen Klassert says:

====================
pull request (net): ipsec 2019-04-30

1) Fix an out-of-bound array accesses in __xfrm_policy_unlink.
   From YueHaibing.

2) Reset the secpath on failure in the ESP GRO handlers
   to avoid dereferencing an invalid pointer on error.
   From Myungho Jung.

3) Add and revert a patch that tried to add rcu annotations
   to netns_xfrm. From Su Yanjun.

4) Wait for rcu callbacks before freeing xfrm6_tunnel_spi_kmem.
   From Su Yanjun.

5) Fix forgotten vti4 ipip tunnel deregistration.
   From Jeremy Sowden:

6) Remove some duplicated log messages in vti4.
   From Jeremy Sowden.

7) Don't use IPSEC_PROTO_ANY when flushing states because
   this will flush only IPsec portocol speciffic states.
   IPPROTO_ROUTING states may remain in the lists when
   doing net exit. Fix this by replacing IPSEC_PROTO_ANY
   with zero. From Cong Wang.

8) Add length check for UDP encapsulation to fix "Oversized IP packet"
   warnings on receive side. From Sabrina Dubroca.

9) Fix xfrm interface lookup when the interface is associated to
   a vrf layer 3 master device. From Martin Willi.

10) Reload header pointers after pskb_may_pull() in _decode_session4(),
    otherwise we may read from uninitialized memory.

11) Update the documentation about xfrm[46]_gc_thresh, it
    is not used anymore after the flowcache removal.
    From Nicolas Dichtel.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Two easy cases of overlapping changes.

Signed-off-by: David S. Miller <davem@davemloft.net>

To make ICMPv6 closer to ICMPv4, add ratemask parameter. Since the ICMP
message types use larger numeric values, a simple bitmask doesn't fit.
I use large bitmap. The input and output are the in form of list of
ranges. Set the default to rate limit all error messages but Packet Too
Big. For Packet Too Big, use ratemask instead of hard-coded.

There are functions where icmpv6_xrlim_allow() and icmpv6_global_allow()
aren't called. This patch only adds them to icmpv6_echo_reply().

Rate limiting error messages is mandated by RFC 4443 but RFC 4890 says
that it is also acceptable to rate limit informational messages. Thus,
I removed the current hard-coded behavior of icmpv6_mask_allow() that
doesn't rate limit informational messages.

v2: Add dummy function proc_do_large_bitmap() if CONFIG_PROC_SYSCTL
    isn't defined, expand the description in ip-sysctl.txt and remove
    unnecessary conditional before kfree().
v3: Inline the bitmap instead of dynamically allocated. Still is a
    pointer to it is needed because of the way proc_do_large_bitmap work.

Signed-off-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

There is a UBSAN report as below:
UBSAN: Undefined behaviour in net/ipv4/tcp_input.c:2877:56
signed integer overflow:
2147483647 * 1000 cannot be represented in type 'int'
CPU: 3 PID: 0 Comm: swapper/3 Not tainted 5.1.0-rc4-00058-g582549e #1
Call Trace:
 <IRQ>
 dump_stack+0x8c/0xba
 ubsan_epilogue+0x11/0x60
 handle_overflow+0x12d/0x170
 ? ttwu_do_wakeup+0x21/0x320
 __ubsan_handle_mul_overflow+0x12/0x20
 tcp_ack_update_rtt+0x76c/0x780
 tcp_clean_rtx_queue+0x499/0x14d0
 tcp_ack+0x69e/0x1240
 ? __wake_up_sync_key+0x2c/0x50
 ? update_group_capacity+0x50/0x680
 tcp_rcv_established+0x4e2/0xe10
 tcp_v4_do_rcv+0x22b/0x420
 tcp_v4_rcv+0xfe8/0x1190
 ip_protocol_deliver_rcu+0x36/0x180
 ip_local_deliver+0x15b/0x1a0
 ip_rcv+0xac/0xd0
 __netif_receive_skb_one_core+0x7f/0xb0
 __netif_receive_skb+0x33/0xc0
 netif_receive_skb_internal+0x84/0x1c0
 napi_gro_receive+0x2a0/0x300
 receive_buf+0x3d4/0x2350
 ? detach_buf_split+0x159/0x390
 virtnet_poll+0x198/0x840
 ? reweight_entity+0x243/0x4b0
 net_rx_action+0x25c/0x770
 __do_softirq+0x19b/0x66d
 irq_exit+0x1eb/0x230
 do_IRQ+0x7a/0x150
 common_interrupt+0xf/0xf
 </IRQ>

It can be reproduced by:
  echo 2147483647 > /proc/sys/net/ipv4/tcp_min_rtt_wlen

Fixes: f672258391b42 ("tcp: track min RTT using windowed min-filter")
Signed-off-by: ZhangXiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Those entries are not used anymore.

CC: Florian Westphal <fw@strlen.de>
Fixes: 09c7570480f7 ("xfrm: remove flow cache")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

fib_trie implementation calls synchronize_rcu when a certain amount of
pages are dirty from freed entries. The number of pages was determined
experimentally in 2009 (commit c3059477fce2d).

At the current setting, synchronize_rcu is called often -- 51 times in a
second in one test with an average of an 8 msec delay adding a fib entry.
The total impact is a lot of slow down modifying the fib. This is seen
in the output of 'time' - the difference between real time and sys+user.
For example, using 720,022 single path routes and 'ip -batch'[1]:

    $ time ./ip -batch ipv4/routes-1-hops
    real    0m14.214s
    user    0m2.513s
    sys     0m6.783s

So roughly 35% of the actual time to install the routes is from the ip
command getting scheduled out, most notably due to synchronize_rcu (this
is observed using 'perf sched timehist').

This patch makes the amount of dirty memory configurable between 64k where
the synchronize_rcu is called often (small, low end systems that are memory
sensitive) to 64M where synchronize_rcu is called rarely during a large
FIB change (for high end systems with lots of memory). The default is 512kB
which corresponds to the current setting of 128 pages with a 4kB page size.

As an example, at 16MB the worst interval shows 4 calls to synchronize_rcu
in a second blocking for up to 30 msec in a single instance, and a total
of almost 100 msec across the 4 calls in the second. The trade off is
allowing FIB entries to consume more memory in a given time window but
but with much better fib insertion rates (~30% increase in prefixes/sec).
With this patch and net.ipv4.fib_sync_mem set to 16MB, the same batch
file runs in:

    $ time ./ip -batch ipv4/routes-1-hops
    real    0m9.692s
    user    0m2.491s
    sys     0m6.769s

So the dead time is reduced to about 1/2 second or <5% of the real time.

[1] 'ip' modified to not request ACK messages which improves route
    insertion times by about 20%

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>