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Date: Tue, 11 Sep 2018 21:02:48 +0200 From: Tobias Hommel <netdev-list@...oetigt.de> To: Wolfgang Walter <linux@...m.de> Cc: Steffen Klassert <steffen.klassert@...unet.com>, Kristian Evensen <kristian.evensen@...il.com>, Network Development <netdev@...r.kernel.org>, weiwan@...gle.com, edumazet@...gle.com Subject: Re: kernels > v4.12 oops/crash with ipsec-traffic: bisected to b838d5e1c5b6e57b10ec8af2268824041e3ea911: ipv4: mark DST_NOGC and remove the operation of dst_free() > > 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 <netdev-list@...oetigt.de> > > Reported-by: Kristian Evensen <kristian.evensen@...il.com> > > Reported-by: Wolfgang Walter <linux@...m.de> > > Signed-off-by: Steffen Klassert <steffen.klassert@...unet.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 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)) { > > This patch fixes the problem here. > > XfrmFwdHdrError gets around 80 at the very beginning and remains so. Probably > this happens when some route are changed/set then. > > Regards and thanks, Same here, we're now running stable for ~6 hours, XfrmFwdHdrError is at 220. This is less than 1 lost packet per minute, which seems to be okay for now.
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