[PATCH] drm: fix mutex leak in drm_dp_get_mst_branch_device

[Jani Nikula]

On Fri, 16 Oct 2015, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Fri, Oct 16, 2015 at 03:33:02AM -0700, Adam Richter wrote:
>> In Linux 4.3-rc5, there is an error case in drm_dp_get_branch_device
>> that returns without releasing mgr->lock, resulting a spew of kernel
>> messages about a kernel work function possibly having leaked a mutex
>> and presumably more serious adverse consequences later.  This patch
>> changes the error to "goto out" to unlock the mutex before returning.
>> 
>> Signed-off-by: Adam J. Richter <adam_richter2004 at yahoo.com>
>
> Patch was whitespace mangled (don't past them into your mailer but instead
> send them with git send-email directly, that's safer), so I had to
> recreate it.
>
> Applied to drm-misc, thanks.

It's missing

Reviewed-by: Jani Nikula <jani.nikula at intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92480
Fixes: 9eb1e57f564d ("drm/dp/mst: take lock around looking up the branch device on hpd irq")
Cc: stable at vger.kernel.org # v4.2+

and arguably was for drm-fixes.

BR,
Jani.



> -Daniel
>
>> ---
>> 
>> bugzilla.freedesktop.org ticket:
>> https://bugs.freedesktop.org/show_bug.cgi?id=92480
>> 
>> This patch is against the latest
>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git .  I
>> apologize in advance in I should be submitting patches against some
>> other reference.  Please feel free to let me know if I should use some
>> other reference for submitting future patches.
>> 
>> My request to subscribe to dri-devel at lists.freedesktop.org is pending,
>> so I apologize if it takes a while for this message to be posted on
>> the mailing list.
>> 
>> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
>> b/drivers/gpu/drm/drm_dp_mst_topology.c
>> index bf27a07..018ad7f 100644
>> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
>> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
>> @@ -1194,17 +1194,18 @@ static struct drm_dp_mst_branch
>> *drm_dp_get_mst_branch_device(struct drm_dp_mst_
>> 
>>                 list_for_each_entry(port, &mstb->ports, next) {
>>                         if (port->port_num == port_num) {
>> -                               if (!port->mstb) {
>> +                               mstb = port->mstb;
>> +                               if (!mstb) {
>>                                         DRM_ERROR("failed to lookup
>> MSTB with lct %d, rad %02x\n", lct, rad[0]);
>> -                                       return NULL;
>> +                                       goto out;
>>                                 }
>> 
>> -                               mstb = port->mstb;
>>                                 break;
>>                         }
>>                 }
>>         }
>>         kref_get(&mstb->kref);
>> + out:
>>         mutex_unlock(&mgr->lock);
>>         return mstb;
>>  }
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
> _______________________________________________
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> dri-devel at lists.freedesktop.org
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-- 
Jani Nikula, Intel Open Source Technology Center