netlink: Fix dump skb leak/double free

commit 92964c79b357efd980812c4de5c1fd2ec8bb5520 upstream.

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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 46cac8e31a16cf335860897fc552ad11870927e0..24876492f26abaf13b29fc4e70329c3d8b17792c 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2693,6 +2693,7 @@ 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_min_size;
        int alloc_size;
@@ -2773,9 +2774,11 @@ 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: