UPSTREAM: netfilter: xt_TCPMSS: add more sanity tests on tcph->doff

Denys provided an awesome KASAN report pointing to an use
after free in xt_TCPMSS

I have provided three patches to fix this issue, either in xt_TCPMSS or
in xt_tcpudp.c. It seems xt_TCPMSS patch has the smallest possible
impact.

BUG=chromium:803812
TEST=Build and run

Change-Id: I2a9ae6a021a3a4ceeb2421ad7b118b1b3ccea8db
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Denys Fedoryshchenko <nuclearcat@nuclearcat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Guenter Roeck <groeck@chromium.org>
(cherry picked from commit 2638fd0f92d4397884fd991d8f4925cb3)
Reviewed-on: https://chromium-review.googlesource.com/879163
1 file changed