| Message ID | 20210623113740.6260-2-desmondcheongzx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm: address potential UAF bugs with drm_master ptrs | expand |
On 23/6/21 7:37 pm, Desmond Cheong Zhi Xi wrote: > While checking the master status of the DRM file in > drm_is_current_master(), the device's master mutex should be > held. Without the mutex, the pointer fpriv->master may be freed > concurrently by another process calling drm_setmaster_ioctl(). This > could lead to use-after-free errors when the pointer is subsequently > dereferenced in drm_lease_owner(). > > The callers of drm_is_current_master() from drm_auth.c hold the > device's master mutex, but external callers do not. Hence, we implement > drm_is_current_master_locked() to be used within drm_auth.c, and > modify drm_is_current_master() to grab the device's master mutex > before checking the master status. > > Additionally, to avoid a circular lock dependency by introducing > drm_device.master_mutex into drm_is_current_master(), we move the call > to drm_is_current_master() in drm_mode_getconnector out from the > section locked by &dev->mode_config.mutex. > > Failing to avoid this lock dependency produces the following lockdep > splat: > > ====================================================== > WARNING: possible circular locking dependency detected > 5.13.0-rc7-CI-CI_DRM_10254+ #1 Not tainted > ------------------------------------------------------ > kms_frontbuffer/1087 is trying to acquire lock: > ffff88810dcd01a8 (&dev->master_mutex){+.+.}-{3:3}, at: drm_is_current_master+0x1b/0x40 > but task is already holding lock: > ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0 > which lock already depends on the new lock. > the existing dependency chain (in reverse order) is: > -> #2 (&dev->mode_config.mutex){+.+.}-{3:3}: > __mutex_lock+0xab/0x970 > drm_client_modeset_probe+0x22e/0xca0 > __drm_fb_helper_initial_config_and_unlock+0x42/0x540 > intel_fbdev_initial_config+0xf/0x20 [i915] > async_run_entry_fn+0x28/0x130 > process_one_work+0x26d/0x5c0 > worker_thread+0x37/0x380 > kthread+0x144/0x170 > ret_from_fork+0x1f/0x30 > -> #1 (&client->modeset_mutex){+.+.}-{3:3}: > __mutex_lock+0xab/0x970 > drm_client_modeset_commit_locked+0x1c/0x180 > drm_client_modeset_commit+0x1c/0x40 > __drm_fb_helper_restore_fbdev_mode_unlocked+0x88/0xb0 > drm_fb_helper_set_par+0x34/0x40 > intel_fbdev_set_par+0x11/0x40 [i915] > fbcon_init+0x270/0x4f0 > visual_init+0xc6/0x130 > do_bind_con_driver+0x1e5/0x2d0 > do_take_over_console+0x10e/0x180 > do_fbcon_takeover+0x53/0xb0 > register_framebuffer+0x22d/0x310 > __drm_fb_helper_initial_config_and_unlock+0x36c/0x540 > intel_fbdev_initial_config+0xf/0x20 [i915] > async_run_entry_fn+0x28/0x130 > process_one_work+0x26d/0x5c0 > worker_thread+0x37/0x380 > kthread+0x144/0x170 > ret_from_fork+0x1f/0x30 > -> #0 (&dev->master_mutex){+.+.}-{3:3}: > __lock_acquire+0x151e/0x2590 > lock_acquire+0xd1/0x3d0 > __mutex_lock+0xab/0x970 > drm_is_current_master+0x1b/0x40 > drm_mode_getconnector+0x37e/0x4a0 > drm_ioctl_kernel+0xa8/0xf0 > drm_ioctl+0x1e8/0x390 > __x64_sys_ioctl+0x6a/0xa0 > do_syscall_64+0x39/0xb0 > entry_SYSCALL_64_after_hwframe+0x44/0xae > other info that might help us debug this: > Chain exists of: &dev->master_mutex --> &client->modeset_mutex --> &dev->mode_config.mutex > Possible unsafe locking scenario: > CPU0 CPU1 > ---- ---- > lock(&dev->mode_config.mutex); > lock(&client->modeset_mutex); > lock(&dev->mode_config.mutex); > lock(&dev->master_mutex); > *** DEADLOCK *** > 1 lock held by kms_frontbuffer/1087: > #0: ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0 > stack backtrace: > CPU: 7 PID: 1087 Comm: kms_frontbuffer Not tainted 5.13.0-rc7-CI-CI_DRM_10254+ #1 > Hardware name: Intel Corporation Ice Lake Client Platform/IceLake U DDR4 SODIMM PD RVP TLC, BIOS ICLSFWR1.R00.3234.A01.1906141750 06/14/2019 > Call Trace: > dump_stack+0x7f/0xad > check_noncircular+0x12e/0x150 > __lock_acquire+0x151e/0x2590 > lock_acquire+0xd1/0x3d0 > __mutex_lock+0xab/0x970 > drm_is_current_master+0x1b/0x40 > drm_mode_getconnector+0x37e/0x4a0 > drm_ioctl_kernel+0xa8/0xf0 > drm_ioctl+0x1e8/0x390 > __x64_sys_ioctl+0x6a/0xa0 > do_syscall_64+0x39/0xb0 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch> > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> > --- > drivers/gpu/drm/drm_auth.c | 51 +++++++++++++++++++++------------ > drivers/gpu/drm/drm_connector.c | 5 +++- > 2 files changed, 36 insertions(+), 20 deletions(-) > > diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c > index f00e5abdbbf4..ab1863c5a5a0 100644 > --- a/drivers/gpu/drm/drm_auth.c > +++ b/drivers/gpu/drm/drm_auth.c > @@ -61,6 +61,35 @@ > * trusted clients. > */ > > +static bool drm_is_current_master_locked(struct drm_file *fpriv) > +{ > + lockdep_assert_held_once(&fpriv->minor->dev->master_mutex); > + > + return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; > +} > + > +/** > + * drm_is_current_master - checks whether @priv is the current master > + * @fpriv: DRM file private > + * > + * Checks whether @fpriv is current master on its device. This decides whether a > + * client is allowed to run DRM_MASTER IOCTLs. > + * > + * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting > + * - the current master is assumed to own the non-shareable display hardware. > + */ > +bool drm_is_current_master(struct drm_file *fpriv) > +{ > + bool ret; > + > + mutex_lock(&fpriv->minor->dev->master_mutex); > + ret = drm_is_current_master_locked(fpriv); > + mutex_unlock(&fpriv->minor->dev->master_mutex); > + > + return ret; > +} > +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; > @@ -223,7 +252,7 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data, > if (ret) > goto out_unlock; > > - if (drm_is_current_master(file_priv)) > + if (drm_is_current_master_locked(file_priv)) > goto out_unlock; > > if (dev->master) { > @@ -272,7 +301,7 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data, > if (ret) > goto out_unlock; > > - if (!drm_is_current_master(file_priv)) { > + if (!drm_is_current_master_locked(file_priv)) { > ret = -EINVAL; > goto out_unlock; > } > @@ -321,7 +350,7 @@ void drm_master_release(struct drm_file *file_priv) > if (file_priv->magic) > idr_remove(&file_priv->master->magic_map, file_priv->magic); > > - if (!drm_is_current_master(file_priv)) > + if (!drm_is_current_master_locked(file_priv)) > goto out; > > drm_legacy_lock_master_cleanup(dev, master); > @@ -342,22 +371,6 @@ void drm_master_release(struct drm_file *file_priv) > mutex_unlock(&dev->master_mutex); > } > > -/** > - * drm_is_current_master - checks whether @priv is the current master > - * @fpriv: DRM file private > - * > - * Checks whether @fpriv is current master on its device. This decides whether a > - * client is allowed to run DRM_MASTER IOCTLs. > - * > - * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting > - * - the current master is assumed to own the non-shareable display hardware. > - */ > -bool drm_is_current_master(struct drm_file *fpriv) > -{ > - return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; > -} > -EXPORT_SYMBOL(drm_is_current_master); > - > /** > * drm_master_get - reference a master pointer > * @master: &struct drm_master > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c > index da39e7ff6965..a5f63bad3893 100644 > --- a/drivers/gpu/drm/drm_connector.c > +++ b/drivers/gpu/drm/drm_connector.c > @@ -2414,6 +2414,7 @@ int drm_mode_getconnector(struct drm_device *dev, void *data, > struct drm_mode_modeinfo u_mode; > struct drm_mode_modeinfo __user *mode_ptr; > uint32_t __user *encoder_ptr; > + bool is_current_master; > > if (!drm_core_check_feature(dev, DRIVER_MODESET)) > return -EOPNOTSUPP; > @@ -2444,9 +2445,11 @@ int drm_mode_getconnector(struct drm_device *dev, void *data, > out_resp->connector_type = connector->connector_type; > out_resp->connector_type_id = connector->connector_type_id; > > + is_current_master = drm_is_current_master(file_priv) > + > mutex_lock(&dev->mode_config.mutex); > if (out_resp->count_modes == 0) { > - if (drm_is_current_master(file_priv)) > + if (is_current_master) > connector->funcs->fill_modes(connector, > dev->mode_config.max_width, > dev->mode_config.max_height); > Hi Daniel, My bad, I just realized that this patch won't apply to stable because of the changes to drm_connector.c. Will the intel-gfx CI apply the patches in order if I break up this patch and move the changes to drm_connector.c earlier in the series? Best wishes, Desmond
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index f00e5abdbbf4..ab1863c5a5a0 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -61,6 +61,35 @@ * trusted clients. */ +static bool drm_is_current_master_locked(struct drm_file *fpriv) +{ + lockdep_assert_held_once(&fpriv->minor->dev->master_mutex); + + return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; +} + +/** + * drm_is_current_master - checks whether @priv is the current master + * @fpriv: DRM file private + * + * Checks whether @fpriv is current master on its device. This decides whether a + * client is allowed to run DRM_MASTER IOCTLs. + * + * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting + * - the current master is assumed to own the non-shareable display hardware. + */ +bool drm_is_current_master(struct drm_file *fpriv) +{ + bool ret; + + mutex_lock(&fpriv->minor->dev->master_mutex); + ret = drm_is_current_master_locked(fpriv); + mutex_unlock(&fpriv->minor->dev->master_mutex); + + return ret; +} +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; @@ -223,7 +252,7 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data, if (ret) goto out_unlock; - if (drm_is_current_master(file_priv)) + if (drm_is_current_master_locked(file_priv)) goto out_unlock; if (dev->master) { @@ -272,7 +301,7 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data, if (ret) goto out_unlock; - if (!drm_is_current_master(file_priv)) { + if (!drm_is_current_master_locked(file_priv)) { ret = -EINVAL; goto out_unlock; } @@ -321,7 +350,7 @@ void drm_master_release(struct drm_file *file_priv) if (file_priv->magic) idr_remove(&file_priv->master->magic_map, file_priv->magic); - if (!drm_is_current_master(file_priv)) + if (!drm_is_current_master_locked(file_priv)) goto out; drm_legacy_lock_master_cleanup(dev, master); @@ -342,22 +371,6 @@ void drm_master_release(struct drm_file *file_priv) mutex_unlock(&dev->master_mutex); } -/** - * drm_is_current_master - checks whether @priv is the current master - * @fpriv: DRM file private - * - * Checks whether @fpriv is current master on its device. This decides whether a - * client is allowed to run DRM_MASTER IOCTLs. - * - * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting - * - the current master is assumed to own the non-shareable display hardware. - */ -bool drm_is_current_master(struct drm_file *fpriv) -{ - return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; -} -EXPORT_SYMBOL(drm_is_current_master); - /** * drm_master_get - reference a master pointer * @master: &struct drm_master diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index da39e7ff6965..a5f63bad3893 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -2414,6 +2414,7 @@ int drm_mode_getconnector(struct drm_device *dev, void *data, struct drm_mode_modeinfo u_mode; struct drm_mode_modeinfo __user *mode_ptr; uint32_t __user *encoder_ptr; + bool is_current_master; if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP; @@ -2444,9 +2445,11 @@ int drm_mode_getconnector(struct drm_device *dev, void *data, out_resp->connector_type = connector->connector_type; out_resp->connector_type_id = connector->connector_type_id; + is_current_master = drm_is_current_master(file_priv) + mutex_lock(&dev->mode_config.mutex); if (out_resp->count_modes == 0) { - if (drm_is_current_master(file_priv)) + if (is_current_master) connector->funcs->fill_modes(connector, dev->mode_config.max_width, dev->mode_config.max_height);
While checking the master status of the DRM file in drm_is_current_master(), the device's master mutex should be held. Without the mutex, the pointer fpriv->master may be freed concurrently by another process calling drm_setmaster_ioctl(). This could lead to use-after-free errors when the pointer is subsequently dereferenced in drm_lease_owner(). The callers of drm_is_current_master() from drm_auth.c hold the device's master mutex, but external callers do not. Hence, we implement drm_is_current_master_locked() to be used within drm_auth.c, and modify drm_is_current_master() to grab the device's master mutex before checking the master status. Additionally, to avoid a circular lock dependency by introducing drm_device.master_mutex into drm_is_current_master(), we move the call to drm_is_current_master() in drm_mode_getconnector out from the section locked by &dev->mode_config.mutex. Failing to avoid this lock dependency produces the following lockdep splat: ====================================================== WARNING: possible circular locking dependency detected 5.13.0-rc7-CI-CI_DRM_10254+ #1 Not tainted ------------------------------------------------------ kms_frontbuffer/1087 is trying to acquire lock: ffff88810dcd01a8 (&dev->master_mutex){+.+.}-{3:3}, at: drm_is_current_master+0x1b/0x40 but task is already holding lock: ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&dev->mode_config.mutex){+.+.}-{3:3}: __mutex_lock+0xab/0x970 drm_client_modeset_probe+0x22e/0xca0 __drm_fb_helper_initial_config_and_unlock+0x42/0x540 intel_fbdev_initial_config+0xf/0x20 [i915] async_run_entry_fn+0x28/0x130 process_one_work+0x26d/0x5c0 worker_thread+0x37/0x380 kthread+0x144/0x170 ret_from_fork+0x1f/0x30 -> #1 (&client->modeset_mutex){+.+.}-{3:3}: __mutex_lock+0xab/0x970 drm_client_modeset_commit_locked+0x1c/0x180 drm_client_modeset_commit+0x1c/0x40 __drm_fb_helper_restore_fbdev_mode_unlocked+0x88/0xb0 drm_fb_helper_set_par+0x34/0x40 intel_fbdev_set_par+0x11/0x40 [i915] fbcon_init+0x270/0x4f0 visual_init+0xc6/0x130 do_bind_con_driver+0x1e5/0x2d0 do_take_over_console+0x10e/0x180 do_fbcon_takeover+0x53/0xb0 register_framebuffer+0x22d/0x310 __drm_fb_helper_initial_config_and_unlock+0x36c/0x540 intel_fbdev_initial_config+0xf/0x20 [i915] async_run_entry_fn+0x28/0x130 process_one_work+0x26d/0x5c0 worker_thread+0x37/0x380 kthread+0x144/0x170 ret_from_fork+0x1f/0x30 -> #0 (&dev->master_mutex){+.+.}-{3:3}: __lock_acquire+0x151e/0x2590 lock_acquire+0xd1/0x3d0 __mutex_lock+0xab/0x970 drm_is_current_master+0x1b/0x40 drm_mode_getconnector+0x37e/0x4a0 drm_ioctl_kernel+0xa8/0xf0 drm_ioctl+0x1e8/0x390 __x64_sys_ioctl+0x6a/0xa0 do_syscall_64+0x39/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Chain exists of: &dev->master_mutex --> &client->modeset_mutex --> &dev->mode_config.mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&dev->mode_config.mutex); lock(&client->modeset_mutex); lock(&dev->mode_config.mutex); lock(&dev->master_mutex); *** DEADLOCK *** 1 lock held by kms_frontbuffer/1087: #0: ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0 stack backtrace: CPU: 7 PID: 1087 Comm: kms_frontbuffer Not tainted 5.13.0-rc7-CI-CI_DRM_10254+ #1 Hardware name: Intel Corporation Ice Lake Client Platform/IceLake U DDR4 SODIMM PD RVP TLC, BIOS ICLSFWR1.R00.3234.A01.1906141750 06/14/2019 Call Trace: dump_stack+0x7f/0xad check_noncircular+0x12e/0x150 __lock_acquire+0x151e/0x2590 lock_acquire+0xd1/0x3d0 __mutex_lock+0xab/0x970 drm_is_current_master+0x1b/0x40 drm_mode_getconnector+0x37e/0x4a0 drm_ioctl_kernel+0xa8/0xf0 drm_ioctl+0x1e8/0x390 __x64_sys_ioctl+0x6a/0xa0 do_syscall_64+0x39/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> --- drivers/gpu/drm/drm_auth.c | 51 +++++++++++++++++++++------------ drivers/gpu/drm/drm_connector.c | 5 +++- 2 files changed, 36 insertions(+), 20 deletions(-)