If first drm_open fails, the error-handling path will incorrectly restore inode's mapping to NULL. This can cause the crash later on. Fix by separately storing away mapping pointers that drm_open can touch and restore each from its own respective variable if the call fails.

Fixes: https://bugzilla.novell.com/show_bug.cgi?id=807850 (thanks to Michal Hocko for investigating investigating and finding the root cause of the bug)

Reference: http://lists.freedesktop.org/archives/dri-devel/2013-March/036564.html

v2: Use one variable to store file and inode mapping since they are the same at the function entry. Fix spelling mistakes in commit message.

v3: Add reference to the original bug report.

Reported-by: Marco Munderloh munderl@tnt.uni-hannover.de Tested-by: Marco Munderloh munderl@tnt.uni-hannover.de Signed-off-by: Ilija Hadzic ihadzic@research.bell-labs.com Cc: Michal Hocko mhocko@suse.cz Cc: stable@vger.kernel.org --- drivers/gpu/drm/drm_fops.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c index 13fdcd1..429e07d 100644 --- a/drivers/gpu/drm/drm_fops.c +++ b/drivers/gpu/drm/drm_fops.c @@ -123,6 +123,7 @@ int drm_open(struct inode *inode, struct file *filp) int retcode = 0; int need_setup = 0; struct address_space *old_mapping; + struct address_space *old_imapping;

minor = idr_find(&drm_minors_idr, minor_id); if (!minor) @@ -137,6 +138,7 @@ int drm_open(struct inode *inode, struct file *filp) if (!dev->open_count++) need_setup = 1; mutex_lock(&dev->struct_mutex); + old_imapping = inode->i_mapping; old_mapping = dev->dev_mapping; if (old_mapping == NULL) dev->dev_mapping = &inode->i_data; @@ -159,8 +161,8 @@ int drm_open(struct inode *inode, struct file *filp)

err_undo: mutex_lock(&dev->struct_mutex); - filp->f_mapping = old_mapping; - inode->i_mapping = old_mapping; + filp->f_mapping = old_imapping; + inode->i_mapping = old_imapping; iput(container_of(dev->dev_mapping, struct inode, i_data)); dev->dev_mapping = old_mapping; mutex_unlock(&dev->struct_mutex);