Re: [PATCH] Drivers: hv: vmbus: Use after free in __vmbus_open()

[Wei Liu]

On Tue, Apr 13, 2021 at 01:50:04PM +0300, Dan Carpenter wrote:
> The "open_info" variable is added to the &vmbus_connection.chn_msg_list,
> but the error handling frees "open_info" without removing it from the
> list.  This will result in a use after free.  First remove it from the
> list, and then free it.
> 
> Fixes: 6f3d791f3006 ("Drivers: hv: vmbus: Fix rescind handling issues")
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
> From static analysis.  Untested etc.  There is almost certainly a good
> reason to add it to the list before checking "newchannel->rescind" but I
> don't know the code well enough to know what the reason is.
> 

AIUI the channel management code requires the message be queued before
posting the message to backend, because processing response is done in
another thread, and might happen before this message is added to the
list if the order is reversed.

>  drivers/hv/channel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> index db30be8f9cce..1c5a418c1962 100644
> --- a/drivers/hv/channel.c
> +++ b/drivers/hv/channel.c
> @@ -653,7 +653,7 @@ static int __vmbus_open(struct vmbus_channel *newchannel,
>  
>  	if (newchannel->rescind) {
>  		err = -ENODEV;
> -		goto error_free_info;
> +		goto error_clean_msglist;

Looking at similar functions in the same file I think there is indeed an
UAF problem in the original code.

I have not studied this piece of code extensively so I will wait for
others to chime in.

Wei.

>  	}
>  
>  	err = vmbus_post_msg(open_msg,
> -- 
> 2.30.2
>