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.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index e75d8e47f35..dac08e2a5a9 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;