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Commit a8ec3a66 authored by Ilija Hadzic's avatar Ilija Hadzic Committed by Dave Airlie
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drm: correctly restore mappings if drm_open fails 

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: default avatarMarco Munderloh <munderl@tnt.uni-hannover.de>
Tested-by: default avatarMarco Munderloh <munderl@tnt.uni-hannover.de>
Signed-off-by: default avatarIlija Hadzic <ihadzic@research.bell-labs.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent 7cebefe6

drivers/gpu/drm/drm_fops.c

+4 −2
Original line number Diff line number Diff line
@@ -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);