From: Eric Dumazet <edumazet@google.com>
Date: Thu, 5 Dec 2019 10:10:15 -0800
Subject: tcp: md5: fix potential overestimation of TCP option space
Git-commit: 9424e2e7ad93ffffa88f882c9bc5023570904b55
Patch-mainline: 5.5-rc1
References: networking-stable-19_12_16
Back in 2008, Adam Langley fixed the corner case of packets for flows
having all of the following options : MD5 TS SACK
Since MD5 needs 20 bytes, and TS needs 12 bytes, no sack block
can be cooked from the remaining 8 bytes.
tcp_established_options() correctly sets opts->num_sack_blocks
to zero, but returns 36 instead of 32.
This means TCP cooks packets with 4 extra bytes at the end
of options, containing unitialized bytes.
Fixes: 33ad798c924b ("tcp: options clean up")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
net/ipv4/tcp_output.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index be6d22b8190f..b184f03d7437 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -755,8 +755,9 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb
min_t(unsigned int, eff_sacks,
(remaining - TCPOLEN_SACK_BASE_ALIGNED) /
TCPOLEN_SACK_PERBLOCK);
- size += TCPOLEN_SACK_BASE_ALIGNED +
- opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
+ if (likely(opts->num_sack_blocks))
+ size += TCPOLEN_SACK_BASE_ALIGNED +
+ opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
}
return size;
--
2.25.0