From: Eric Dumazet edumazet@google.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@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: Greg Kroah-Hartman gregkh@linuxfoundation.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 @@ -740,8 +740,9 @@ 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;