| Message ID | 20210818073824.1560124-5-desmondcheongzx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm, kernel: update locking for DRM | expand |
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@gmail.com> >> --- >> 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 >> >
On Wed, Aug 18, 2021 at 5:37 PM Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote: > > 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@gmail.com> > >> --- > >> 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. Do we have to? If I haven't missed anything, the drm_client stuff only calls drm_file_alloc and doesn't set up a master. So this should work? -Daniel > > > > >> + > >> 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 > >> > > >
On 19/8/21 12:33 am, Daniel Vetter wrote: > On Wed, Aug 18, 2021 at 5:37 PM Desmond Cheong Zhi Xi > <desmondcheongzx@gmail.com> wrote: >> >> 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@gmail.com> >>>> --- >>>> 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. > > Do we have to? > > If I haven't missed anything, the drm_client stuff only calls > drm_file_alloc and doesn't set up a master. So this should work? > -Daniel > Ahhhh ok yes, I understand what's going on better now. I think you're right, moving drm_master_release into drm_close_helper should fix all the places it can go wrong. >> >>> >>>> + >>>> 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 >>>> >>> >> > >
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; + 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);
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. 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@gmail.com> --- drivers/gpu/drm/drm_auth.c | 16 ++++++++++++++-- drivers/gpu/drm/drm_ioctl.c | 5 +++++ 2 files changed, 19 insertions(+), 2 deletions(-)