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>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index aeefe127691a8f14f132a5c6db8ad3e8a68d546a..627f898c05b96552318a881ce995ccc3342e1576 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2059,6 +2059,7 @@ 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;
@@ -2134,9 +2135,11 @@ 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: