[PATCH] drm: fix mutex leak in drm_dp_get_mst_branch_device

[Adam Richter]

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>
---

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;
 }