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

Message ID 1486235812.21871.145.camel@edumazet-glaptop3.roam.corp.google.com
State Accepted
Delegated to: David Miller
Headers show

Commit Message

Eric Dumazet Feb. 4, 2017, 7:16 p.m.
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 <andreyknvl@google.com>
---
 net/ipv4/ip_sockglue.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Comments

David Miller Feb. 5, 2017, 12:43 a.m. | #1
From: Eric Dumazet <eric.dumazet@gmail.com>
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 <andreyknvl@google.com>

Applied and queued up for -stable, thanks.

Patch

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 8a4409dd390aac7fcb88383af1550a2f967d..c4fcf9d713cca64a3afaec1628692739d9fa 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1243,7 +1243,14 @@  void ipv4_pktinfo_prepare(const struct sock *sk, 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,