[PATCH] xfrm_user: return error pointer instead of NULL

When dump_one_state() returns an error, e.g. because of a too small
buffer to dump the whole xfrm state, xfrm_state_netlink() returns NULL
instead of an error pointer. But its callers expect an error pointer
and therefore continue to operate on a NULL skbuff.

This could lead to a privilege escalation (execution of user code in
kernel context) if the attacker has CAP_NET_ADMIN and is able to map
address 0.

Cc: stable@vger.kernel.org
Signed-off-by: Mathias Krause <redacted>
---

A test case can be provided on request.

 net/xfrm/xfrm_user.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index e75d8e4..dac08e2 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c

@@ -878,6 +878,7 @@ static struct sk_buff *xfrm_state_netlink(struct sk_buff *in_skb,
 {
 	struct xfrm_dump_info info;
 	struct sk_buff *skb;
+	int err;
 
 	skb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
 	if (!skb)

@@ -888,9 +889,10 @@ static struct sk_buff *xfrm_state_netlink(struct sk_buff *in_skb,
 	info.nlmsg_seq = seq;
 	info.nlmsg_flags = 0;
 
-	if (dump_one_state(x, 0, &info)) {
+	err = dump_one_state(x, 0, &info);
+	if (err) {
 		kfree_skb(skb);
-		return NULL;
+		return ERR_PTR(err);
 	}
 
 	return skb;

-- 
1.7.10.4

On Thu, Sep 13, 2012 at 11:41:26PM +0200, Mathias Krause wrote:

When dump_one_state() returns an error, e.g. because of a too small
buffer to dump the whole xfrm state, xfrm_state_netlink() returns NULL
instead of an error pointer. But its callers expect an error pointer
and therefore continue to operate on a NULL skbuff.

This could lead to a privilege escalation (execution of user code in
kernel context) if the attacker has CAP_NET_ADMIN and is able to map
address 0.

Or it simply crashes with a NULL pointer dereference.

Cc: stable@vger.kernel.org
Signed-off-by: Mathias Krause <redacted>

Acked-by: Steffen Klassert <steffen.klassert@secunet.com>

On Mon, Sep 17, 2012 at 9:16 AM, Steffen Klassert
[off-list ref] wrote:

On Thu, Sep 13, 2012 at 11:41:26PM +0200, Mathias Krause wrote:

quoted

When dump_one_state() returns an error, e.g. because of a too small
buffer to dump the whole xfrm state, xfrm_state_netlink() returns NULL
instead of an error pointer. But its callers expect an error pointer
and therefore continue to operate on a NULL skbuff.

This could lead to a privilege escalation (execution of user code in
kernel context) if the attacker has CAP_NET_ADMIN and is able to map
address 0.

Or it simply crashes with a NULL pointer dereference.

..while holding the xfrm_cfg_mutex, therefore effectively disabling
the XFRM netlink interface. So it's at least a DOS in that case ;)

Regards,
Mathias

From: Steffen Klassert <steffen.klassert@secunet.com>
Date: Mon, 17 Sep 2012 09:16:42 +0200

On Thu, Sep 13, 2012 at 11:41:26PM +0200, Mathias Krause wrote:

quoted

When dump_one_state() returns an error, e.g. because of a too small
buffer to dump the whole xfrm state, xfrm_state_netlink() returns NULL
instead of an error pointer. But its callers expect an error pointer
and therefore continue to operate on a NULL skbuff.

This could lead to a privilege escalation (execution of user code in
kernel context) if the attacker has CAP_NET_ADMIN and is able to map
address 0.

Or it simply crashes with a NULL pointer dereference.

quoted

Cc: stable@vger.kernel.org
Signed-off-by: Mathias Krause <redacted>

Acked-by: Steffen Klassert <steffen.klassert@secunet.com>

Applied, and queued up for -stable.

Please do not CC: stable explicitly in your patch submissions,
I removed it from the patch.

Instead, ask me to queue the patch up for -stable.  We handle stable
submissed via a patch queue which I maintain at:

	http://patchwork.ozlabs.org/user/bundle/2566/?state=*

so that I can let patches cook in Linus's tree for a length of
time of my choosing, rather than having bug fixes automatically
propagate the moment it hits Linus's tree.

Thanks.