On Mon, Sep 10, 2018 at 10:18:47AM +0200, Kristian Evensen wrote:
> Hi,
>
> Thanks everyone for all the effort in debugging this issue.
>
> On Mon, Sep 10, 2018 at 8:39 AM Steffen Klassert
> <[email protected]> wrote:
> > The easy fix that could be backported to stable would be
> > to check skb->dst for NULL and drop the packet in that case.
>
> Thought I should just chime in and say that we deployed this
> work-around when we started observing the error back in June. Since
> then we have not seen any crashes. Also, we have instrumented some of
> our kernels to count the number of times the error is hit (overall +
> consecutive). Compared to the overall number of packets, the error
> happens very rarely. With our workloads, we on average see the error
> once every couple of days.
Thanks for letting us know!
I plan to fix this in the ipsec tree with:
Subject: [PATCH RFC] xfrm: Fix NULL pointer dereference when skb_dst_force
clears
the dst_entry.
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 <[email protected]>
Reported-by: Kristian Evensen <[email protected]>
Reported-by: Wolfgang Walter <[email protected]>
Signed-off-by: Steffen Klassert <[email protected]>
---
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 89b178a78dc7..36d15a38ce5e 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 7c5e8978aeaa..626e0f4d1749 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2548,6 +2548,10 @@ 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)) {
--
2.17.1
