Re: [PATCH] drm: fix mutex leak in drm_dp_get_mst_branch_device

[Daniel Vetter <daniel@ffwll.ch>]

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@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.
-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@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;
>  }
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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