Re: AF_KEY: memory leak in key_notify_policy

[Steffen Klassert]

On Tue, Jan 09, 2018 at 06:23:54PM +0100, Dmitry Vyukov wrote:
> Hello,
> 
> syzkaller has hit the following memory leak on 4.15-rc7:
> 
> unreferenced object 0xffff88001ea69cc0 (size 232):
>   comm "syz-executor6", pid 4338, jiffies 4294719848 (age 11.965s)
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<000000004139cfa6>] kmemleak_alloc_recursive
> include/linux/kmemleak.h:55 [inline]
>     [<000000004139cfa6>] slab_post_alloc_hook mm/slab.h:440 [inline]
>     [<000000004139cfa6>] slab_alloc_node mm/slub.c:2725 [inline]
>     [<000000004139cfa6>] kmem_cache_alloc_node+0x12d/0x2a0 mm/slub.c:2761
>     [<0000000071fee1f9>] __alloc_skb+0x103/0x7c0 net/core/skbuff.c:193
>     [<00000000b7305c65>] alloc_skb include/linux/skbuff.h:983 [inline]
>     [<00000000b7305c65>] pfkey_xfrm_policy2msg_prep+0x29/0x50
> net/key/af_key.c:2029
>     [<000000008b2518b3>] key_notify_policy net/key/af_key.c:2192 [inline]
>     [<000000008b2518b3>] pfkey_send_policy_notify+0x47f/0x920
> net/key/af_key.c:3065
>     [<0000000038eae3c6>] km_policy_notify+0x198/0x330 net/xfrm/xfrm_state.c:1907
>     [<000000000c1a40c2>] xfrm_add_policy+0x733/0x9a0 net/xfrm/xfrm_user.c:1613
>     [<000000001c692c3f>] xfrm_user_rcv_msg+0x454/0x890 net/xfrm/xfrm_user.c:2591
>     [<0000000048c3aba7>] netlink_rcv_skb+0x275/0x550
> net/netlink/af_netlink.c:2408
>     [<00000000649d0c12>] xfrm_netlink_rcv+0x6f/0x90 net/xfrm/xfrm_user.c:2599
>     [<00000000c67992ca>] netlink_unicast_kernel
> net/netlink/af_netlink.c:1275 [inline]
>     [<00000000c67992ca>] netlink_unicast+0x567/0x710
> net/netlink/af_netlink.c:1301
>     [<00000000614f28d1>] netlink_sendmsg+0x9c4/0xf60
> net/netlink/af_netlink.c:1864
>     [<000000004abc1891>] sock_sendmsg_nosec net/socket.c:636 [inline]
>     [<000000004abc1891>] sock_sendmsg+0xd2/0x120 net/socket.c:646
>     [<0000000067a5f2bd>] ___sys_sendmsg+0x7f6/0x930 net/socket.c:2026
>     [<00000000ba6aef1c>] __sys_sendmsg+0xe6/0x220 net/socket.c:2060
>     [<0000000051af4885>] SYSC_sendmsg net/socket.c:2071 [inline]
>     [<0000000051af4885>] SyS_sendmsg+0x36/0x60 net/socket.c:2067
>     [<00000000e00c5f48>] entry_SYSCALL_64_fastpath+0x23/0x9a
> 
> It seems that key_notify_policy() fails to free the skb when
> pfkey_xfrm_policy2msg() fails.

Right, I plan to fix it with the following patch:

Subject: [PATCH] af_key: Fix memory leak in key_notify_policy.

We leak the allocated out_skb in case
pfkey_xfrm_policy2msg() fails. Fix this
by freeing it on error.

Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
---
 net/key/af_key.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/key/af_key.c b/net/key/af_key.c
index d40861a048fe..7e2e7188e7f4 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -2202,8 +2202,10 @@ static int key_notify_policy(struct xfrm_policy *xp, int dir, const struct km_ev
 		return PTR_ERR(out_skb);
 
 	err = pfkey_xfrm_policy2msg(out_skb, xp, dir);
-	if (err < 0)
+	if (err < 0) {
+		kfree_skb(out_skb);
 		return err;
+	}
 
 	out_hdr = (struct sadb_msg *) out_skb->data;
 	out_hdr->sadb_msg_version = PF_KEY_V2;
-- 
2.14.1