ipv4: keep skb->dst around in presence of IP options

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")

Bug 1954563

Change-Id: If36b48f68fccfa194b207872f1c3e9369d5f4723
Reviewed-on: https://git-master.nvidia.com/r/1530408
GVS: Gerrit_Virtual_Submit
Reviewed-by: James Huang <jamehuang@nvidia.com>
Tested-by: James Huang <jamehuang@nvidia.com>
Reviewed-by: Hayden Du <haydend@nvidia.com>
1 file changed