Commit 9cfcca23 authored Jan 09, 2020 by Mat Martineau Committed by David S. Miller Jan 09, 2020

tcp: Check for filled TCP option space before SACK



Update the SACK check to work with zero option space available, a case
that's possible with MPTCP but not MD5+TS. Maintained only one
conditional branch for insufficient SACK space.

v1 -> v2:
- Moves the check inside the SACK branch by taking recent SACK fix:

    9424e2e7 (tcp: md5: fix potential overestimation of TCP option space)

  in to account, but modifies it to work in MPTCP scenarios beyond the
  MD5+TS corner case.

Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 35b2c321

net/ipv4/tcp_output.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -754,11 +754,15 @@ static unsigned int tcp_established_options(struct sock sk, struct sk_buff skb
		eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
		if (unlikely(eff_sacks)) {
		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
		if (unlikely(remaining < TCPOLEN_SACK_BASE_ALIGNED +
		TCPOLEN_SACK_PERBLOCK))
		return size;

		opts->num_sack_blocks =
		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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