linux-kernel - Re: [PATCH net v3] 9p/xen : Fix use after free bug in xen_9pfs_front

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Date:   Mon, 13 Mar 2023 15:53:20 +0100
From:   Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
To:     Zheng Wang <zyytlz.wz@....com>
Cc:     ericvh@...il.com, lucho@...kov.net, asmadeus@...ewreck.org,
        linux_oss@...debyte.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com,
        v9fs-developer@...ts.sourceforge.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, hackerzheng666@...il.com,
        1395428693sheep@...il.com, alex000young@...il.com
Subject: Re: [PATCH net v3] 9p/xen : Fix use after free bug in
 xen_9pfs_front_remove  due  to race condition

On Mon, Mar 13, 2023 at 10:43:25PM +0800, Zheng Wang wrote:
> In xen_9pfs_front_probe, it calls xen_9pfs_front_alloc_dataring
> to init priv->rings and bound &ring->work with p9_xen_response.
> 
> When it calls xen_9pfs_front_event_handler to handle IRQ requests,
> it will finally call schedule_work to start the work.
> 
> When we call xen_9pfs_front_remove to remove the driver, there
> may be a sequence as follows:
> 
> Fix it by finishing the work before cleanup in xen_9pfs_front_free.
> 
> Note that, this bug is found by static analysis, which might be
> false positive.
> 
> CPU0                  CPU1
> 
>                      |p9_xen_response
> xen_9pfs_front_remove|
>   xen_9pfs_front_free|
> kfree(priv)          |
> //free priv          |
>                      |p9_tag_lookup
>                      |//use priv->client
> 
> Fixes: 71ebd71921e4 ("xen/9pfs: connect to the backend")
> Signed-off-by: Zheng Wang <zyytlz.wz@....com>
> ---
> v3:
> - remove unnecessary comment and move definition to the
> for loop suggested by Michal Swiatkowski
> 
> v2:
> - fix type error of ring found by kernel test robot
> ---
>  net/9p/trans_xen.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
[...]

Thanks for changes
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>