Commit 9424e2e7 authored Dec 05, 2019 by Eric Dumazet Committed by David S. Miller Dec 06, 2019

tcp: md5: fix potential overestimation of TCP option space



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: 33ad798c ("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>

parent 9a74542e

net/ipv4/tcp_output.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -755,6 +755,7 @@ 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);
		if (likely(opts->num_sack_blocks))
		size += TCPOLEN_SACK_BASE_ALIGNED +
		opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
		}

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