Re: [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested()
From: Wangshaobo (bobo)
Date: Thu Jul 15 2021 - 00:58:01 EST
在 2021/7/15 5:50, Luiz Augusto von Dentz 写道:
Hi,
On Tue, Jul 13, 2021 at 8:20 PM Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx> wrote:
use-after-free error in lock_sock_nested() is reported:
[ 179.140137][ T3731] =====================================================
[ 179.142675][ T3731] BUG: KMSAN: use-after-free in lock_sock_nested+0x280/0x2c0
[ 179.145494][ T3731] CPU: 4 PID: 3731 Comm: kworker/4:2 Not tainted 5.12.0-rc6+ #54
[ 179.148432][ T3731] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
[ 179.151806][ T3731] Workqueue: events l2cap_chan_timeout
[ 179.152730][ T3731] Call Trace:
[ 179.153301][ T3731] dump_stack+0x24c/0x2e0
[ 179.154063][ T3731] kmsan_report+0xfb/0x1e0
[ 179.154855][ T3731] __msan_warning+0x5c/0xa0
[ 179.155579][ T3731] lock_sock_nested+0x280/0x2c0
[ 179.156436][ T3731] ? kmsan_get_metadata+0x116/0x180
[ 179.157257][ T3731] l2cap_sock_teardown_cb+0xb8/0x890
[ 179.158154][ T3731] ? __msan_metadata_ptr_for_load_8+0x10/0x20
[ 179.159141][ T3731] ? kmsan_get_metadata+0x116/0x180
[ 179.159994][ T3731] ? kmsan_get_shadow_origin_ptr+0x84/0xb0
[ 179.160959][ T3731] ? l2cap_sock_recv_cb+0x420/0x420
[ 179.161834][ T3731] l2cap_chan_del+0x3e1/0x1d50
[ 179.162608][ T3731] ? kmsan_get_metadata+0x116/0x180
[ 179.163435][ T3731] ? kmsan_get_shadow_origin_ptr+0x84/0xb0
[ 179.164406][ T3731] l2cap_chan_close+0xeea/0x1050
[ 179.165189][ T3731] ? kmsan_internal_unpoison_shadow+0x42/0x70
[ 179.166180][ T3731] l2cap_chan_timeout+0x1da/0x590
[ 179.167066][ T3731] ? __msan_metadata_ptr_for_load_8+0x10/0x20
[ 179.168023][ T3731] ? l2cap_chan_create+0x560/0x560
[ 179.168818][ T3731] process_one_work+0x121d/0x1ff0
[ 179.169598][ T3731] worker_thread+0x121b/0x2370
[ 179.170346][ T3731] kthread+0x4ef/0x610
[ 179.171010][ T3731] ? process_one_work+0x1ff0/0x1ff0
[ 179.171828][ T3731] ? kthread_blkcg+0x110/0x110
[ 179.172587][ T3731] ret_from_fork+0x1f/0x30
[ 179.173348][ T3731]
[ 179.173752][ T3731] Uninit was created at:
[ 179.174409][ T3731] kmsan_internal_poison_shadow+0x5c/0xf0
[ 179.175373][ T3731] kmsan_slab_free+0x76/0xc0
[ 179.176060][ T3731] kfree+0x3a5/0x1180
[ 179.176664][ T3731] __sk_destruct+0x8af/0xb80
[ 179.177375][ T3731] __sk_free+0x812/0x8c0
[ 179.178032][ T3731] sk_free+0x97/0x130
[ 179.178686][ T3731] l2cap_sock_release+0x3d5/0x4d0
[ 179.179457][ T3731] sock_close+0x150/0x450
[ 179.180117][ T3731] __fput+0x6bd/0xf00
[ 179.180787][ T3731] ____fput+0x37/0x40
[ 179.181481][ T3731] task_work_run+0x140/0x280
[ 179.182219][ T3731] do_exit+0xe51/0x3e60
[ 179.182930][ T3731] do_group_exit+0x20e/0x450
[ 179.183656][ T3731] get_signal+0x2dfb/0x38f0
[ 179.184344][ T3731] arch_do_signal_or_restart+0xaa/0xe10
[ 179.185266][ T3731] exit_to_user_mode_prepare+0x2d2/0x560
[ 179.186136][ T3731] syscall_exit_to_user_mode+0x35/0x60
[ 179.186984][ T3731] do_syscall_64+0xc5/0x140
[ 179.187681][ T3731] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 179.188604][ T3731] =====================================================
In our case, there are two Thread A and B:
Context: Thread A: Context: Thread B:
l2cap_chan_timeout() __se_sys_shutdown()
l2cap_chan_close() l2cap_sock_shutdown()
l2cap_chan_del() l2cap_chan_close()
l2cap_sock_teardown_cb() l2cap_sock_teardown_cb()
Once l2cap_sock_teardown_cb() excuted, this sock will be marked as SOCK_ZAPPED,
and can be treated as killable in l2cap_sock_kill() if sock_orphan() has
excuted, at this time we close sock through sock_close() which end to call
l2cap_sock_kill() like Thread C:
Context: Thread C:
sock_close()
l2cap_sock_release()
sock_orphan()
l2cap_sock_kill() #free sock if refcnt is 1
If C completed, Once A or B reaches l2cap_sock_teardown_cb() again,
use-after-free happened.
We should set chan->data to NULL if sock is freed, for telling teardown
operation is not allowed in l2cap_sock_teardown_cb(), and also we should
avoid killing an already killed socket in l2cap_sock_close_cb().
Signed-off-by: Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx>
---
net/bluetooth/l2cap_sock.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index c99d65ef13b1..ddc6a692b237 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1215,14 +1215,18 @@ static int l2cap_sock_recvmsg(struct socket *sock, struct msghdr *msg,
*/
static void l2cap_sock_kill(struct sock *sk)
{
+ struct l2cap_chan *chan;
+
if (!sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket)
return;
BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state));
/* Kill poor orphan */
-
- l2cap_chan_put(l2cap_pi(sk)->chan);
+ chan = l2cap_pi(sk)->chan;
+ l2cap_chan_put(chan);
There is a problem here, the above sentence `l2cap_chan_put(chan)`
should put after
following sentence.
+ if (refcount_read(&sk->sk_refcnt) == 1)
+ chan->data = NULL;
Instead of checking if it is the last reference here, wouldn't it be
better to reset the chan->data to NULL on l2cap_sock_destruct?
Hi,
In my case it looks OK, this is the diff:
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index f1b1edd0b697..32ef3328ab49 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1500,6 +1500,9 @@ static void l2cap_sock_close_cb(struct l2cap_chan
*chan)
{
struct sock *sk = chan->data;
+ if (!sk)
+ return;
+
l2cap_sock_kill(sk);
}
@@ -1508,6 +1511,9 @@ static void l2cap_sock_teardown_cb(struct
l2cap_chan *chan, int err)
struct sock *sk = chan->data;
struct sock *parent;
+ if (!sk)
+ return;
+
BT_DBG("chan %p state %s", chan, state_to_string(chan->state));
/* This callback can be called both for server (BT_LISTEN)
@@ -1700,6 +1706,7 @@ static void l2cap_sock_destruct(struct sock *sk)
BT_DBG("sk %p", sk);
if (l2cap_pi(sk)->chan)
+ l2cap_pi(sk)->chan->data = NULL;
l2cap_chan_put(l2cap_pi(sk)->chan);
But if it has potential risk if l2cap_sock_destruct() can not be excuted
in time ?
sk_free():
if (refcount_dec_and_test(&sk->sk_wmem_alloc)) //is possible
this condition false ?
__sk_free(sk) -> ... l2cap_sock_destruct()