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Message-Id: <20191219183225.513466043@linuxfoundation.org>
Date: Thu, 19 Dec 2019 19:34:21 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
syzbot <syzkaller@...glegroups.com>,
Neal Cardwell <ncardwell@...gle.com>,
Soheil Hassas Yeganeh <soheil@...gle.com>,
"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 179/199] tcp: md5: fix potential overestimation of TCP option space
From: Eric Dumazet <edumazet@...gle.com>
[ Upstream commit 9424e2e7ad93ffffa88f882c9bc5023570904b55 ]
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@...gle.com>
Reported-by: syzbot <syzkaller@...glegroups.com>
Acked-by: Neal Cardwell <ncardwell@...gle.com>
Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
net/ipv4/tcp_output.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -707,8 +707,9 @@ static unsigned int tcp_established_opti
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;
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