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.

Reported-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com --- drivers/gpu/drm/drm_auth.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index 232abbba3686..c6bf52c310a9 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -61,6 +61,8 @@ * trusted clients. */

+static bool drm_is_current_master_locked(struct drm_file *fpriv); + int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) { struct drm_auth *auth = data; @@ -223,7 +225,7 @@ 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 +274,7 @@ 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 +323,7 @@ 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); @@ -342,6 +344,13 @@ void drm_master_release(struct drm_file *file_priv) mutex_unlock(&dev->master_mutex); }

+static bool drm_is_current_master_locked(struct drm_file *fpriv) +{ + lockdep_assert_held_once(&fpriv->master->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 @@ -354,7 +363,13 @@ void drm_master_release(struct drm_file *file_priv) */ bool drm_is_current_master(struct drm_file *fpriv) { - return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master; + bool ret; + + mutex_lock(&fpriv->master->dev->master_mutex); + ret = drm_is_current_master_locked(fpriv); + mutex_unlock(&fpriv->master->dev->master_mutex); + + return ret; } EXPORT_SYMBOL(drm_is_current_master);

This patch ensures that the device's master mutex is acquired before accessing pointers to struct drm_master that are subsequently dereferenced. Without the mutex, the struct drm_master may be freed concurrently by another process calling drm_setmaster_ioctl(). This could then lead to use-after-free errors.

Reported-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com --- drivers/gpu/drm/drm_lease.c | 58 +++++++++++++++++++++++++++---------- 1 file changed, 43 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c index da4f085fc09e..f2422f1c4915 100644 --- a/drivers/gpu/drm/drm_lease.c +++ b/drivers/gpu/drm/drm_lease.c @@ -107,10 +107,16 @@ static bool _drm_has_leased(struct drm_master *master, int id) */ bool _drm_lease_held(struct drm_file *file_priv, int id) { + bool ret; + if (!file_priv || !file_priv->master) return true;

- return _drm_lease_held_master(file_priv->master, id); + mutex_lock(&file_priv->master->dev->master_mutex); + ret = _drm_lease_held_master(file_priv->master, id); + mutex_unlock(&file_priv->master->dev->master_mutex); + + return ret; }

/** @@ -132,10 +138,12 @@ bool drm_lease_held(struct drm_file *file_priv, int id) if (!file_priv || !file_priv->master || !file_priv->master->lessor) return true;

+ mutex_lock(&file_priv->master->dev->master_mutex); master = file_priv->master; mutex_lock(&master->dev->mode_config.idr_mutex); ret = _drm_lease_held_master(master, id); mutex_unlock(&master->dev->mode_config.idr_mutex); + mutex_unlock(&file_priv->master->dev->master_mutex); return ret; }

@@ -158,6 +166,7 @@ uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs_in) if (!file_priv || !file_priv->master || !file_priv->master->lessor) return crtcs_in;

+ mutex_lock(&file_priv->master->dev->master_mutex); master = file_priv->master; dev = master->dev;

@@ -177,6 +186,7 @@ uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs_in) count_in++; } mutex_unlock(&master->dev->mode_config.idr_mutex); + mutex_unlock(&file_priv->master->dev->master_mutex); return crtcs_out; }

@@ -490,7 +500,7 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, size_t object_count; int ret = 0; struct idr leases; - struct drm_master *lessor = lessor_priv->master; + struct drm_master *lessor; struct drm_master *lessee = NULL; struct file *lessee_file = NULL; struct file *lessor_file = lessor_priv->filp; @@ -502,12 +512,6 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP;

- /* Do not allow sub-leases */ - if (lessor->lessor) { - DRM_DEBUG_LEASE("recursive leasing not allowed\n"); - return -EINVAL; - } - /* need some objects */ if (cl->object_count == 0) { DRM_DEBUG_LEASE("no objects in lease\n"); @@ -519,12 +523,23 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, return -EINVAL; }

+ mutex_lock(&dev->master_mutex); + lessor = lessor_priv->master; + /* Do not allow sub-leases */ + if (lessor->lessor) { + DRM_DEBUG_LEASE("recursive leasing not allowed\n"); + ret = -EINVAL; + goto unlock; + } + object_count = cl->object_count;

object_ids = memdup_user(u64_to_user_ptr(cl->object_ids), array_size(object_count, sizeof(__u32))); - if (IS_ERR(object_ids)) - return PTR_ERR(object_ids); + if (IS_ERR(object_ids)) { + ret = PTR_ERR(object_ids); + goto unlock; + }

idr_init(&leases);

@@ -535,14 +550,15 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, if (ret) { DRM_DEBUG_LEASE("lease object lookup failed: %i\n", ret); idr_destroy(&leases); - return ret; + goto unlock; }

/* Allocate a file descriptor for the lease */ fd = get_unused_fd_flags(cl->flags & (O_CLOEXEC | O_NONBLOCK)); if (fd < 0) { idr_destroy(&leases); - return fd; + ret = fd; + goto unlock; }

DRM_DEBUG_LEASE("Creating lease\n"); @@ -578,6 +594,7 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, /* Hook up the fd */ fd_install(fd, lessee_file);

+ mutex_unlock(&dev->master_mutex); DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n"); return 0;

@@ -587,6 +604,8 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, out_leases: put_unused_fd(fd);

+unlock: + mutex_unlock(&dev->master_mutex); DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl failed: %d\n", ret); return ret; } @@ -609,7 +628,7 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, struct drm_mode_list_lessees *arg = data; __u32 __user *lessee_ids = (__u32 __user *) (uintptr_t) (arg->lessees_ptr); __u32 count_lessees = arg->count_lessees; - struct drm_master *lessor = lessor_priv->master, *lessee; + struct drm_master *lessor, *lessee; int count; int ret = 0;

@@ -620,6 +639,8 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP;

+ mutex_lock(&dev->master_mutex); + lessor = lessor_priv->master; DRM_DEBUG_LEASE("List lessees for %d\n", lessor->lessee_id);

mutex_lock(&dev->mode_config.idr_mutex); @@ -643,6 +664,7 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, arg->count_lessees = count;

mutex_unlock(&dev->mode_config.idr_mutex); + mutex_unlock(&dev->master_mutex);

return ret; } @@ -662,7 +684,7 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, struct drm_mode_get_lease *arg = data; __u32 __user *object_ids = (__u32 __user *) (uintptr_t) (arg->objects_ptr); __u32 count_objects = arg->count_objects; - struct drm_master *lessee = lessee_priv->master; + struct drm_master *lessee; struct idr *object_idr; int count; void *entry; @@ -678,8 +700,10 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev,

DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id);

+ mutex_lock(&dev->master_mutex); mutex_lock(&dev->mode_config.idr_mutex);

+ lessee = lessee_priv->master; if (lessee->lessor == NULL) /* owner can use all objects */ object_idr = &lessee->dev->mode_config.object_idr; @@ -703,6 +727,7 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, arg->count_objects = count;

mutex_unlock(&dev->mode_config.idr_mutex); + mutex_unlock(&dev->master_mutex);

return ret; } @@ -721,7 +746,7 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, void *data, struct drm_file *lessor_priv) { struct drm_mode_revoke_lease *arg = data; - struct drm_master *lessor = lessor_priv->master; + struct drm_master *lessor; struct drm_master *lessee; int ret = 0;

@@ -731,8 +756,10 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP;

+ mutex_lock(&dev->master_mutex); mutex_lock(&dev->mode_config.idr_mutex);

+ lessor = lessor_priv->master; lessee = _drm_find_lessee(lessor, arg->lessee_id);

/* No such lessee */ @@ -751,6 +778,7 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev,

fail: mutex_unlock(&dev->mode_config.idr_mutex); + mutex_unlock(&dev->master_mutex);

return ret; }