drm: Fix authentication kernel crash

BugLink: http://bugs.launchpad.net/bugs/926309

commit 598781d71119827b454fd75d46f84755bca6f0c6 upstream.

If the master tries to authenticate a client using drm_authmagic and
that client has already closed its drm file descriptor,
either wilfully or because it was terminated, the
call to drm_authmagic will dereference a stale pointer into kmalloc'ed memory
and corrupt it.

Typically this results in a hard system hang.

This patch fixes that problem by removing any authentication tokens
(struct drm_magic_entry) open for a file descriptor when that file
descriptor is closed.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index fbd640dbf7e..c282f85c1c8 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -490,6 +490,11 @@ int drm_release(struct inode *inode, struct file *filp)
                   (long)old_encode_dev(file_priv->minor->device),
                   dev->open_count);
 
+        /* Release any auth tokens that might point to this file_priv,
+           (do that under the drm_global_mutex) */
+        if (file_priv->magic)
+                (void) drm_remove_magic(file_priv->master, file_priv->magic);
+
         /* if the master has gone away we can't do anything with the lock */
         if (file_priv->minor->master)
                 drm_master_release(dev, filp);