On 18/8/21 6:11 pm, Daniel Vetter wrote:
On Wed, Aug 18, 2021 at 03:38:19PM +0800, Desmond Cheong Zhi Xi wrote:
There are three areas where we dereference struct drm_master without
checking if the pointer is non-NULL.
1. drm_getmagic is called from the ioctl_handler. Since
DRM_IOCTL_GET_MAGIC has no ioctl flags, drm_getmagic is run without
any check that drm_file.master has been set.
2. Similarly, drm_getunique is called from the ioctl_handler, but
DRM_IOCTL_GET_UNIQUE has no ioctl flags. So there is no guarantee that
drm_file.master has been set.
I think the above two are impossible, due to the refcounting rules for
struct file.
Right, will drop those two parts from the patch.
3. drm_master_release can also be called without having a
drm_file.master set. Here is one error path:
drm_open():
drm_open_helper():
drm_master_open():
drm_new_set_master(); <--- returns -ENOMEM,
drm_file.master not set
drm_file_free():
drm_master_release(); <--- NULL ptr dereference
(file_priv->master->magic_map)
Fix these by checking if the master pointers are NULL before use.
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
---
drivers/gpu/drm/drm_auth.c | 16 ++++++++++++++--
drivers/gpu/drm/drm_ioctl.c | 5 +++++
2 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index f9267b21556e..b7230604496b 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -95,11 +95,18 @@ EXPORT_SYMBOL(drm_is_current_master);
int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
{
struct drm_auth *auth = data;
+ struct drm_master *master;
int ret = 0;
mutex_lock(&dev->master_mutex);
+ master = file_priv->master;
+ if (!master) {
+ mutex_unlock(&dev->master_mutex);
+ return -EINVAL;
+ }
+
if (!file_priv->magic) {
- ret = idr_alloc(&file_priv->master->magic_map, file_priv,
+ ret = idr_alloc(&master->magic_map, file_priv,
1, 0, GFP_KERNEL);
if (ret >= 0)
file_priv->magic = ret;
@@ -355,8 +362,12 @@ void drm_master_release(struct drm_file *file_priv)
mutex_lock(&dev->master_mutex);
master = file_priv->master;
+
+ if (!master)
+ goto unlock;
This is a bit convoluted, since we're in the single-threaded release path
we don't need any locking for file_priv related things. Therefore we can
pull the master check out and just directly return.
But since it's a bit surprising maybe a comment that this can happen when
drm_master_open in drm_open_helper fails?
Sounds good. This can actually also happen in the failure path of
mock_drm_getfile if anon_inode_getfile fails. I'll leave a short note
about both of them.
Another option, and maybe cleaner, would be to move the drm_master_release
from drm_file_free into drm_close_helper. That would be fully symmetrical
and should also fix the bug here?
-Daniel
Hmmm maybe the first option to move the check out of the lock might be
better. If I'm not wrong, we would otherwise also need to move
drm_master_release into drm_client_close.
+
if (file_priv->magic)
- idr_remove(&file_priv->master->magic_map, file_priv->magic);
+ idr_remove(&master->magic_map, file_priv->magic);
if (!drm_is_current_master_locked(file_priv))
goto out;
@@ -379,6 +390,7 @@ void drm_master_release(struct drm_file *file_priv)
drm_master_put(&file_priv->master);
spin_unlock(&dev->master_lookup_lock);
}
+unlock:
mutex_unlock(&dev->master_mutex);
}
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 26f3a9ede8fe..4d029d3061d9 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -121,6 +121,11 @@ int drm_getunique(struct drm_device *dev, void *data,
mutex_lock(&dev->master_mutex);
master = file_priv->master;
+ if (!master) {
+ mutex_unlock(&dev->master_mutex);
+ return -EINVAL;
+ }
+
if (u->unique_len >= master->unique_len) {
if (copy_to_user(u->unique, master->unique, master->unique_len)) {
mutex_unlock(&dev->master_mutex);
--
2.25.1
