Linux Virtualization - Mar 2018 - [PATCH net V2] vhost: correctly remove wait queue during poll failure

We tried to remove vq poll from wait queue, but do not check whether
or not it was in a list before. This will lead double free. Fixing
this by switching to use vhost_poll_stop() which zeros poll->wqh after
removing poll from waitqueue to make sure it won't be freed twice.

Cc: Darren Kenny <darren.kenny at oracle.com>
Reported-by: syzbot+c0272972b01b872e604a at syzkaller.appspotmail.com
Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting
backend")
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
Changes from V1:
- tweak the commit log for to match the code
---
 drivers/vhost/vhost.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 1b3e8d2d..5d5a9d9 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll, struct file
*file)
 	if (mask)
 		vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
 	if (mask & EPOLLERR) {
-		if (poll->wqh)
-			remove_wait_queue(poll->wqh, &poll->wait);
+		vhost_poll_stop(poll);
 		ret = -EINVAL;
 	}
 
-- 
2.7.4

On Tue, Mar 27, 2018 at 08:50:52PM +0800, Jason Wang
wrote:
> We tried to remove vq poll from wait queue, but do not check whether
> or not it was in a list before. This will lead double free. Fixing
> this by switching to use vhost_poll_stop() which zeros poll->wqh after
> removing poll from waitqueue to make sure it won't be freed twice.
> 
> Cc: Darren Kenny <darren.kenny at oracle.com>
> Reported-by: syzbot+c0272972b01b872e604a at syzkaller.appspotmail.com
> Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting
backend")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
> Changes from V1:
> - tweak the commit log for to match the code
> ---
>  drivers/vhost/vhost.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 1b3e8d2d..5d5a9d9 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll, struct
file *file)
>  	if (mask)
>  		vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
>  	if (mask & EPOLLERR) {
> -		if (poll->wqh)
> -			remove_wait_queue(poll->wqh, &poll->wait);
> +		vhost_poll_stop(poll);
>  		ret = -EINVAL;
>  	}
>  
> -- 
> 2.7.4

From: Jason Wang <jasowang at redhat.com>
Date: Tue, 27 Mar 2018 20:50:52 +0800
> We tried to remove vq poll from wait queue, but do not check whether
> or not it was in a list before. This will lead double free. Fixing
> this by switching to use vhost_poll_stop() which zeros poll->wqh after
> removing poll from waitqueue to make sure it won't be freed twice.
> 
> Cc: Darren Kenny <darren.kenny at oracle.com>
> Reported-by: syzbot+c0272972b01b872e604a at syzkaller.appspotmail.com
> Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting
backend")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
> Changes from V1:
> - tweak the commit log for to match the code
Applied and queued up for -stable, thank you.

On Tue, Mar 27, 2018 at 08:50:52PM +0800, Jason Wang
wrote:
> We tried to remove vq poll from wait queue, but do not check whether
> or not it was in a list before. This will lead double free. Fixing
> this by switching to use vhost_poll_stop() which zeros poll->wqh after
> removing poll from waitqueue to make sure it won't be freed twice.
> 
> Cc: Darren Kenny <darren.kenny at oracle.com>
> Reported-by: syzbot+c0272972b01b872e604a at syzkaller.appspotmail.com
> Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting
backend")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
OK with this the only bug we have is where get user pages returns 0
(Reported-by: syzbot+6304bf97ef436580fede at syzkaller.appspotmail.com)


> ---
> Changes from V1:
> - tweak the commit log for to match the code
> ---
>  drivers/vhost/vhost.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 1b3e8d2d..5d5a9d9 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll, struct
file *file)
>  	if (mask)
>  		vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
>  	if (mask & EPOLLERR) {
> -		if (poll->wqh)
> -			remove_wait_queue(poll->wqh, &poll->wait);
> +		vhost_poll_stop(poll);
>  		ret = -EINVAL;
>  	}
>  
> -- 
> 2.7.4

On 2018?03?29? 12:20, Michael S. Tsirkin wrote:
> On Tue, Mar 27, 2018 at 08:50:52PM +0800, Jason Wang wrote:
>> We tried to remove vq poll from wait queue, but do not check whether
>> or not it was in a list before. This will lead double free. Fixing
>> this by switching to use vhost_poll_stop() which zeros poll->wqh
after
>> removing poll from waitqueue to make sure it won't be freed twice.
>>
>> Cc: Darren Kenny<darren.kenny at oracle.com>
>> Reported-by:syzbot+c0272972b01b872e604a at syzkaller.appspotmail.com
>> Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when
setting backend")
>> Signed-off-by: Jason Wang<jasowang at redhat.com>
> OK with this the only bug we have is where get user pages returns 0
> (Reported-by:syzbot+6304bf97ef436580fede at syzkaller.appspotmail.com)
>
>
>
Thanks for the reminder.

I post a patch to avoid this.