[SRU][Xenial][Bionic][Cosmic][PATCH] xfrm: Fix NULL pointer dereference when skb_dst_force clears the dst_entry.
Gavin Guo
gavin.guo at canonical.com
Tue Nov 6 14:46:34 UTC 2018
From: Steffen Klassert <steffen.klassert at secunet.com>
BugLink: https://bugs.launchpad.net/bugs/1801878
Since commit 222d7dbd258d ("net: prevent dst uses after free")
skb_dst_force() might clear the dst_entry attached to the skb.
The xfrm code don't expect this to happen, so we crash with
a NULL pointer dereference in this case. Fix it by checking
skb_dst(skb) for NULL after skb_dst_force() and drop the packet
in cast the dst_entry was cleared.
Fixes: 222d7dbd258d ("net: prevent dst uses after free")
Reported-by: Tobias Hommel <netdev-list at genoetigt.de>
Reported-by: Kristian Evensen <kristian.evensen at gmail.com>
Reported-by: Wolfgang Walter <linux at stwm.de>
Signed-off-by: Steffen Klassert <steffen.klassert at secunet.com>
(cherry picked from commit 9e1437937807b0122e8da1ca8765be2adca9aee6)
Signed-off-by: Gavin Guo <gavin.guo at canonical.com>
---
net/xfrm/xfrm_output.c | 4 ++++
net/xfrm/xfrm_policy.c | 4 ++++
2 files changed, 8 insertions(+)
diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index 35610cc881a9..c47660fba498 100644
--- a/net/xfrm/xfrm_output.c
+++ b/net/xfrm/xfrm_output.c
@@ -101,6 +101,10 @@ static int xfrm_output_one(struct sk_buff *skb, int err)
spin_unlock_bh(&x->lock);
skb_dst_force(skb);
+ if (!skb_dst(skb)) {
+ XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTERROR);
+ goto error_nolock;
+ }
if (xfrm_offload(skb)) {
x->type_offload->encap(x, skb);
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 7bcd6f1b86a0..1690efebba8a 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2544,6 +2544,10 @@ int __xfrm_route_forward(struct sk_buff *skb, unsigned short family)
}
skb_dst_force(skb);
+ if (!skb_dst(skb)) {
+ XFRM_INC_STATS(net, LINUX_MIB_XFRMFWDHDRERROR);
+ return 0;
+ }
dst = xfrm_lookup(net, skb_dst(skb), &fl, NULL, XFRM_LOOKUP_QUEUE);
if (IS_ERR(dst)) {
--
2.7.4
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