netlink: Fix dump skb leak/double free

When we free cb->skb after a dump, we do it after releasing the
lock.  This means that a new dump could have started in the time
being and we'll end up freeing their skb instead of ours.

This patch saves the skb and module before we unlock so we free
the right memory.

Fixes: 16b304f3404f ("netlink: Eliminate kmalloc in netlink dump operation.")
Reported-by: Baozeng Ding <sploving1@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 92964c79b357efd980812c4de5c1fd2ec8bb5520)

Orabug: 25203221
CVE: CVE-2016-9806
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index bf6e76643f7876d8dee4df261baf077aad837be3..0ee6712e4094e7fa658d47bb72561552a01f4c05 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2628,6 +2628,7 @@ static int netlink_dump(struct sock *sk)
        struct netlink_callback *cb;
        struct sk_buff *skb = NULL;
        struct nlmsghdr *nlh;
+       struct module *module;
        int len, err = -ENOBUFS;
        int alloc_size;
 
@@ -2697,9 +2698,11 @@ static int netlink_dump(struct sock *sk)
                cb->done(cb);
 
        nlk->cb_running = false;
+       module = cb->module;
+       skb = cb->skb;
        mutex_unlock(nlk->cb_mutex);
-       module_put(cb->module);
-       consume_skb(cb->skb);
+       module_put(module);
+       consume_skb(skb);
        return 0;
 
 errout_skb: