Subject: Re: [PATCH] net: key: af_key: Fix possible null-pointer dereferences in pfkey_send_policy_notify()

From: Jeremy Sowden <[email-masked]>
Date: Fri, 26 Jul 2019 21:15:55 +0100

On 2019-07-26, at 11:45:14 +0200, Steffen Klassert wrote:
> On Wed, Jul 24, 2019 at 05:35:09PM +0800, Jia-Ju Bai wrote:
> > In pfkey_send_policy_notify(), there is an if statement on line 3081
> > to check whether xp is NULL:
> >     if (xp && xp->type != XFRM_POLICY_TYPE_MAIN)
> >
> > When xp is NULL, it is used by key_notify_policy() on line 3090:
> >     key_notify_policy(xp, ...)
> >         pfkey_xfrm_policy2msg_prep(xp) -- line 2211
> >             pfkey_xfrm_policy2msg_size(xp) -- line 2046
> >                 for (i=0; i<xp->xfrm_nr; i++) -- line 2026
> >                 t = xp->xfrm_vec + i; -- line 2027
> >     key_notify_policy(xp, ...)
> >         xp_net(xp) -- line 2231
> >             return read_pnet(&xp->xp_net); -- line 534
>
> Please don't quote random code lines, explain the problem instead.
>
> >
> > Thus, possible null-pointer dereferences may occur.
> >
> > To fix these bugs, xp is checked before calling key_notify_policy().
> >
> > These bugs are found by a static analysis tool STCheck written by
> > us.
> >
> > Signed-off-by: Jia-Ju Bai <[email-masked]>
> > ---
> >  net/key/af_key.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/net/key/af_key.c b/net/key/af_key.c
> > index b67ed3a8486c..ced54144d5fd 100644
> > --- a/net/key/af_key.c
> > +++ b/net/key/af_key.c
> > @@ -3087,6 +3087,8 @@ static int pfkey_send_policy_notify(struct xfrm_policy *xp, int dir, const struc
> >  	case XFRM_MSG_DELPOLICY:
> >  	case XFRM_MSG_NEWPOLICY:
> >  	case XFRM_MSG_UPDPOLICY:
> > +		if (!xp)
> > +			break;
>
> I think this can not happen. Who sends one of these notifications
> without a pointer to the policy?

I had a quick grep and found two places where km_policy_notify is passed
NULL as the policy:

  $ grep -rn '\<km_policy_notify(NULL,' net/
  net/xfrm/xfrm_user.c:2154:      km_policy_notify(NULL, 0, &c);
  net/key/af_key.c:2788:  km_policy_notify(NULL, 0, &c);

They occur in xfrm_flush_policy() and pfkey_spdflush() respectively.

J.