From: Eric Dumazet <edumazet@xxxxxxxxxx> 3.12-stable review patch. If anyone has any objections, please let me know. =============== [ Upstream commit 34b2cef20f19c87999fff3da4071e66937db9644 ] 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@xxxxxxxxxx> Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- net/ipv4/ip_sockglue.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c index 9e4f832aaf13..5a7bb6cb22bb 100644 --- a/net/ipv4/ip_sockglue.c +++ b/net/ipv4/ip_sockglue.c @@ -1044,7 +1044,14 @@ void ipv4_pktinfo_prepare(struct sk_buff *skb) pktinfo->ipi_ifindex = 0; pktinfo->ipi_spec_dst.s_addr = 0; } - skb_dst_drop(skb); + /* We need to keep the dst for __ip_options_echo() + * We could restrict the test to opt.ts_needtime || opt.srr, + * but the following is good enough as IP options are not often used. + */ + if (unlikely(IPCB(skb)->opt.optlen)) + skb_dst_force(skb); + else + skb_dst_drop(skb); } int ip_setsockopt(struct sock *sk, int level, -- 2.12.0