net: avoid signed overflows for SO_{SND|RCV}BUFFORCE

net: avoid signed overflows for SO_{SND|RCV}BUFFORCE

CAP_NET_ADMIN users should not be allowed to set negative
sk_sndbuf or sk_rcvbuf values, as it can lead to various memory
corruptions, crashes, OOM...

Note that before commit 82981930125a ("net: cleanups in
sock_setsockopt()"), the bug was even more serious, since SO_SNDBUF
and SO_RCVBUF were vulnerable.

This needs to be backported to all known linux kernels.

Again, many thanks to syzkaller team for discovering this gem.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit b98b0bc8c431e3ceb4b26b0dfc8db509518fb290)

Orabug: 25203090
CVE: CVE-2016-9793
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>