Re: kernels > v4.12 oops/crash with ipsec-traffic: bisected to b838d5e1c5b6e57b10ec8af2268824041e3ea911: ipv4: mark DST_NOGC and remove the operation of dst_free()

[Tobias Hommel <netdev-list@genoetigt.de>]

> > 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@genoetigt.de>
> > Reported-by: Kristian Evensen <kristian.evensen@gmail.com>
> > Reported-by: Wolfgang Walter <linux@stwm.de>
> > Signed-off-by: Steffen Klassert <steffen.klassert@secunet.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.