Re: [PATH net] ipv4: keep skb->dst around in presence of IP options

From: Eric Dumazet <redacted>
Date: Sat, 04 Feb 2017 11:16:52 -0800

From: Eric Dumazet <edumazet@google.com>

Andrey Konovalov got crashes in __ip_options_echo() when a NULL skb->dst
is accessed.

ipv4_pktinfo_prepare() should not drop the dst if (evil) IP options
are present.

We could refine the test to the presence of ts_needtime or srr,
but IP options are not often used, so let's be conservative.

Thanks to syzkaller team for finding this bug.

Fixes: d826eb14ecef ("ipv4: PKTINFO doesnt need dst reference")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andrey Konovalov <redacted>

Applied and queued up for -stable, thanks.