Commit 34b2cef2 authored Feb 04, 2017 by Eric Dumazet Committed by David S. Miller Feb 04, 2017

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: d826eb14 ("ipv4: PKTINFO doesnt need dst reference")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 5fa8bbda

net/ipv4/ip_sockglue.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -1238,6 +1238,13 @@ void ipv4_pktinfo_prepare(const struct sock sk, struct sk_buff skb)
		pktinfo->ipi_ifindex = 0;
		pktinfo->ipi_spec_dst.s_addr = 0;
		}
		/* 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);
		}

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