[PATCH 3.16 088/305] netlink: Fix dump skb leak/double free

Ben Hutchings
2016-08-14T11:55:27Z

From: Herbert Xu <herbert@gondor.apana.org.au>

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>
---
net/netlink/af_netlink.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- 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;