* [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested()
@ 2021-07-14 3:17 Wang ShaoBo
2021-07-14 21:50 ` Luiz Augusto von Dentz
0 siblings, 1 reply; 6+ messages in thread
From: Wang ShaoBo @ 2021-07-14 3:17 UTC (permalink / raw)
Cc: cj.chengjian, weiyongjun1, yuehaibing, huawei.libin, marcel,
luiz.dentz, johan.hedberg, linux-bluetooth, netdev, linux-kernel
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@huawei.com>
---
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);
+ if (refcount_read(&sk->sk_refcnt) == 1)
+ chan->data = NULL;
sock_set_flag(sk, SOCK_DEAD);
sock_put(sk);
}
@@ -1508,6 +1512,9 @@ static void l2cap_sock_close_cb(struct l2cap_chan *chan)
{
struct sock *sk = chan->data;
+ if (!sk)
+ return;
+
l2cap_sock_kill(sk);
}
@@ -1516,6 +1523,9 @@ 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)
--
2.27.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested()
2021-07-14 3:17 [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested() Wang ShaoBo
@ 2021-07-14 21:50 ` Luiz Augusto von Dentz
2021-07-15 4:57 ` Wangshaobo (bobo)
0 siblings, 1 reply; 6+ messages in thread
From: Luiz Augusto von Dentz @ 2021-07-14 21:50 UTC (permalink / raw)
To: Wang ShaoBo
Cc: cj.chengjian, Wei Yongjun, yuehaibing, huawei.libin,
Marcel Holtmann, Johan Hedberg, linux-bluetooth,
open list:NETWORKING [GENERAL],
Linux Kernel Mailing List
Hi,
On Tue, Jul 13, 2021 at 8:20 PM Wang ShaoBo <bobo.shaobowang@huawei.com> 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@huawei.com>
> ---
> 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);
> + 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?
> sock_set_flag(sk, SOCK_DEAD);
> sock_put(sk);
> }
> @@ -1508,6 +1512,9 @@ static void l2cap_sock_close_cb(struct l2cap_chan *chan)
> {
> struct sock *sk = chan->data;
>
> + if (!sk)
> + return;
> +
> l2cap_sock_kill(sk);
> }
>
> @@ -1516,6 +1523,9 @@ 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)
> --
> 2.27.0
>
--
Luiz Augusto von Dentz
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested()
2021-07-14 21:50 ` Luiz Augusto von Dentz
@ 2021-07-15 4:57 ` Wangshaobo (bobo)
2021-07-16 1:37 ` Wangshaobo (bobo)
0 siblings, 1 reply; 6+ messages in thread
From: Wangshaobo (bobo) @ 2021-07-15 4:57 UTC (permalink / raw)
To: Luiz Augusto von Dentz
Cc: cj.chengjian, Wei Yongjun, yuehaibing, huawei.libin,
Marcel Holtmann, Johan Hedberg, linux-bluetooth,
open list:NETWORKING [GENERAL],
Linux Kernel Mailing List
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@huawei.com> 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@huawei.com>
>> ---
>> 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()
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested()
2021-07-15 4:57 ` Wangshaobo (bobo)
@ 2021-07-16 1:37 ` Wangshaobo (bobo)
2021-07-16 17:22 ` Luiz Augusto von Dentz
0 siblings, 1 reply; 6+ messages in thread
From: Wangshaobo (bobo) @ 2021-07-16 1:37 UTC (permalink / raw)
To: Luiz Augusto von Dentz
Cc: cj.chengjian, Wei Yongjun, yuehaibing, huawei.libin,
Marcel Holtmann, Johan Hedberg, linux-bluetooth,
open list:NETWORKING [GENERAL],
Linux Kernel Mailing List
在 2021/7/15 12:57, Wangshaobo (bobo) 写道:
>
> 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@huawei.com> 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@huawei.com>
>>> ---
>>> 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()
>
Dear Luiz,
Not only that, if l2cap_sock_kill() has put 'l2cap_pi(sk)->chan', how
does we avoid re-puting 'l2cap_pi(sk)->chan' if l2cap_sock_destruct()
work postponed? this will cause underflow of chan->refcount; this PATCH
4e1a720d0312 ("Bluetooth: avoid killing an already killed socket") also
may not work in any case because only sock_orphan() has excuted can this
sock be killed, but if sco_sock_release() excute first, for this sock
has been marked as SOCK_DEAD, this sock can never be killed. So should
we think put chan->data = NULL in xx_sock_kill() is a better choice ?
- WangShaoBo
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested()
2021-07-16 1:37 ` Wangshaobo (bobo)
@ 2021-07-16 17:22 ` Luiz Augusto von Dentz
2021-07-19 2:09 ` Wangshaobo (bobo)
0 siblings, 1 reply; 6+ messages in thread
From: Luiz Augusto von Dentz @ 2021-07-16 17:22 UTC (permalink / raw)
To: Wangshaobo (bobo)
Cc: cj.chengjian, Wei Yongjun, yuehaibing, huawei.libin,
Marcel Holtmann, Johan Hedberg, linux-bluetooth,
open list:NETWORKING [GENERAL],
Linux Kernel Mailing List
Hi,
On Thu, Jul 15, 2021 at 6:38 PM Wangshaobo (bobo)
<bobo.shaobowang@huawei.com> wrote:
>
>
> 在 2021/7/15 12:57, Wangshaobo (bobo) 写道:
> >
> > 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@huawei.com> 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@huawei.com>
> >>> ---
> >>> 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()
> >
> Dear Luiz,
>
> Not only that, if l2cap_sock_kill() has put 'l2cap_pi(sk)->chan', how
> does we avoid re-puting 'l2cap_pi(sk)->chan' if l2cap_sock_destruct()
> work postponed? this will cause underflow of chan->refcount; this PATCH
> 4e1a720d0312 ("Bluetooth: avoid killing an already killed socket") also
> may not work in any case because only sock_orphan() has excuted can this
> sock be killed, but if sco_sock_release() excute first, for this sock
> has been marked as SOCK_DEAD, this sock can never be killed. So should
> we think put chan->data = NULL in xx_sock_kill() is a better choice ?
Not sure what do you mean by postponed? Interrupted perhaps? Even in
that case what are trying to prevent is use after free so if the
callback has not run yet that means the sk has not been freed. Anyway
I think we could do it inconditionally in l2cap_sock_kill since we
will be releasing the reference owned by l2cap_pi(sk)->chan->data that
should be reset to NULL immediatelly.
> - WangShaoBo
>
--
Luiz Augusto von Dentz
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested()
2021-07-16 17:22 ` Luiz Augusto von Dentz
@ 2021-07-19 2:09 ` Wangshaobo (bobo)
0 siblings, 0 replies; 6+ messages in thread
From: Wangshaobo (bobo) @ 2021-07-19 2:09 UTC (permalink / raw)
To: Luiz Augusto von Dentz
Cc: cj.chengjian, Wei Yongjun, yuehaibing, huawei.libin,
Marcel Holtmann, Johan Hedberg, linux-bluetooth,
open list:NETWORKING [GENERAL],
Linux Kernel Mailing List
>>> 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()
>>>
>> Dear Luiz,
>>
>> Not only that, if l2cap_sock_kill() has put 'l2cap_pi(sk)->chan', how
>> does we avoid re-puting 'l2cap_pi(sk)->chan' if l2cap_sock_destruct()
>> work postponed? this will cause underflow of chan->refcount; this PATCH
>> 4e1a720d0312 ("Bluetooth: avoid killing an already killed socket") also
>> may not work in any case because only sock_orphan() has excuted can this
>> sock be killed, but if sco_sock_release() excute first, for this sock
>> has been marked as SOCK_DEAD, this sock can never be killed. So should
>> we think put chan->data = NULL in xx_sock_kill() is a better choice ?
> Not sure what do you mean by postponed? Interrupted perhaps? Even in
> that case what are trying to prevent is use after free so if the
> callback has not run yet that means the sk has not been freed. Anyway
> I think we could do it inconditionally in l2cap_sock_kill since we
> will be releasing the reference owned by l2cap_pi(sk)->chan->data that
> should be reset to NULL immediatelly.
Dear Luiz,
yes, that's right, if sk can be accessed, it also means that chan has
not been destroyed, thanks very much.
-- Wang ShaoBo
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-07-19 2:09 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-07-14 3:17 [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested() Wang ShaoBo
2021-07-14 21:50 ` Luiz Augusto von Dentz
2021-07-15 4:57 ` Wangshaobo (bobo)
2021-07-16 1:37 ` Wangshaobo (bobo)
2021-07-16 17:22 ` Luiz Augusto von Dentz
2021-07-19 2:09 ` Wangshaobo (bobo)
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