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drm: Fix authentication kernel crash

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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 <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>
Cc: [email protected]
Signed-off-by: Dave Airlie <[email protected]>
This commit is contained in:
Thomas Hellstrom 2012-01-24 18:54:21 +01:00 • committed by Dave Airlie
commit 598781d711
3 changed files with 11 additions and 1 deletions
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6
drivers/gpu/drm/drm_auth.c
View file

@ -101,7 +101,7 @@ static int drm_add_magic(struct drm_master *master, struct drm_file *priv,
* Searches and unlinks the entry in drm_device::magiclist with the magic
* number hash key, while holding the drm_device::struct_mutex lock.
*/
static int drm_remove_magic(struct drm_master *master, drm_magic_t magic)
int drm_remove_magic(struct drm_master *master, drm_magic_t magic)
{
struct drm_magic_entry *pt;
struct drm_hash_item *hash;
@ -136,6 +136,8 @@ static int drm_remove_magic(struct drm_master *master, drm_magic_t magic)
* If there is a magic number in drm_file::magic then use it, otherwise
* searches an unique non-zero magic number and add it associating it with \p
* file_priv.
* This ioctl needs protection by the drm_global_mutex, which protects
* struct drm_file::magic and struct drm_magic_entry::priv.
*/
int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
{
@ -173,6 +175,8 @@ int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
* \return zero if authentication successed, or a negative number otherwise.
*
* Checks if \p file_priv is associated with the magic number passed in \arg.
* This ioctl needs protection by the drm_global_mutex, which protects
* struct drm_file::magic and struct drm_magic_entry::priv.
*/
int drm_authmagic(struct drm_device *dev, void *data,
struct drm_file *file_priv)

5
drivers/gpu/drm/drm_fops.c
View file

@ -487,6 +487,11 @@ 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);