From: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com
[ Upstream commit 56f0729a510f92151682ff6c89f69724d5595d6e ]
drm_file->master pointers should be protected by drm_device.master_mutex or drm_file.master_lookup_lock when being dereferenced.
However, in drm_lease.c, there are multiple instances where drm_file->master is accessed and dereferenced while neither lock is held. This makes drm_lease.c vulnerable to use-after-free bugs.
We address this issue in 2 ways:
1. Add a new drm_file_get_master() function that calls drm_master_get on drm_file->master while holding on to drm_file.master_lookup_lock. Since drm_master_get increments the reference count of master, this prevents master from being freed until we unreference it with drm_master_put.
2. In each case where drm_file->master is directly accessed and eventually dereferenced in drm_lease.c, we wrap the access in a call to the new drm_file_get_master function, then unreference the master pointer once we are done using it.
Reported-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com Reviewed-by: Emil Velikov emil.l.velikov@gmail.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Link: https://patchwork.freedesktop.org/patch/msgid/20210712043508.11584-6-desmond... Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/drm_auth.c | 25 ++++++++++++ drivers/gpu/drm/drm_lease.c | 81 ++++++++++++++++++++++++++++--------- include/drm/drm_auth.h | 1 + include/drm/drm_file.h | 6 +++ 4 files changed, 93 insertions(+), 20 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index 0024ad93d24b..c7adbeaf10b1 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -376,6 +376,31 @@ struct drm_master *drm_master_get(struct drm_master *master) } EXPORT_SYMBOL(drm_master_get);
+/** + * drm_file_get_master - reference &drm_file.master of @file_priv + * @file_priv: DRM file private + * + * Increments the reference count of @file_priv's &drm_file.master and returns + * the &drm_file.master. If @file_priv has no &drm_file.master, returns NULL. + * + * Master pointers returned from this function should be unreferenced using + * drm_master_put(). + */ +struct drm_master *drm_file_get_master(struct drm_file *file_priv) +{ + struct drm_master *master = NULL; + + spin_lock(&file_priv->master_lookup_lock); + if (!file_priv->master) + goto unlock; + master = drm_master_get(file_priv->master); + +unlock: + spin_unlock(&file_priv->master_lookup_lock); + return master; +} +EXPORT_SYMBOL(drm_file_get_master); + static void drm_master_destroy(struct kref *kref) { struct drm_master *master = container_of(kref, struct drm_master, refcount); diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c index da4f085fc09e..aef22634005e 100644 --- a/drivers/gpu/drm/drm_lease.c +++ b/drivers/gpu/drm/drm_lease.c @@ -107,10 +107,19 @@ static bool _drm_has_leased(struct drm_master *master, int id) */ bool _drm_lease_held(struct drm_file *file_priv, int id) { - if (!file_priv || !file_priv->master) + bool ret; + struct drm_master *master; + + if (!file_priv) return true;
- return _drm_lease_held_master(file_priv->master, id); + master = drm_file_get_master(file_priv); + if (!master) + return true; + ret = _drm_lease_held_master(master, id); + drm_master_put(&master); + + return ret; }
/** @@ -129,13 +138,22 @@ bool drm_lease_held(struct drm_file *file_priv, int id) struct drm_master *master; bool ret;
- if (!file_priv || !file_priv->master || !file_priv->master->lessor) + if (!file_priv) return true;
- master = file_priv->master; + master = drm_file_get_master(file_priv); + if (!master) + return true; + if (!master->lessor) { + ret = true; + goto out; + } mutex_lock(&master->dev->mode_config.idr_mutex); ret = _drm_lease_held_master(master, id); mutex_unlock(&master->dev->mode_config.idr_mutex); + +out: + drm_master_put(&master); return ret; }
@@ -155,10 +173,16 @@ uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs_in) int count_in, count_out; uint32_t crtcs_out = 0;
- if (!file_priv || !file_priv->master || !file_priv->master->lessor) + if (!file_priv) return crtcs_in;
- master = file_priv->master; + master = drm_file_get_master(file_priv); + if (!master) + return crtcs_in; + if (!master->lessor) { + crtcs_out = crtcs_in; + goto out; + } dev = master->dev;
count_in = count_out = 0; @@ -177,6 +201,9 @@ 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); + +out: + drm_master_put(&master); return crtcs_out; }
@@ -490,7 +517,7 @@ 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 +529,6 @@ 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 +540,22 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, return -EINVAL; }
+ lessor = drm_file_get_master(lessor_priv); + /* Do not allow sub-leases */ + if (lessor->lessor) { + DRM_DEBUG_LEASE("recursive leasing not allowed\n"); + ret = -EINVAL; + goto out_lessor; + } + 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 out_lessor; + }
idr_init(&leases);
@@ -535,14 +566,15 @@ 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 out_lessor; }
/* 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 out_lessor; }
DRM_DEBUG_LEASE("Creating lease\n"); @@ -578,6 +610,7 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, /* Hook up the fd */ fd_install(fd, lessee_file);
+ drm_master_put(&lessor); DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n"); return 0;
@@ -587,6 +620,8 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, out_leases: put_unused_fd(fd);
+out_lessor: + drm_master_put(&lessor); DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl failed: %d\n", ret); return ret; } @@ -609,7 +644,7 @@ 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 +655,7 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP;
+ lessor = drm_file_get_master(lessor_priv); DRM_DEBUG_LEASE("List lessees for %d\n", lessor->lessee_id);
mutex_lock(&dev->mode_config.idr_mutex); @@ -643,6 +679,7 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, arg->count_lessees = count;
mutex_unlock(&dev->mode_config.idr_mutex); + drm_master_put(&lessor);
return ret; } @@ -662,7 +699,7 @@ 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; @@ -676,6 +713,7 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP;
+ lessee = drm_file_get_master(lessee_priv); DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id);
mutex_lock(&dev->mode_config.idr_mutex); @@ -703,6 +741,7 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, arg->count_objects = count;
mutex_unlock(&dev->mode_config.idr_mutex); + drm_master_put(&lessee);
return ret; } @@ -721,7 +760,7 @@ 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;
@@ -731,6 +770,7 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP;
+ lessor = drm_file_get_master(lessor_priv); mutex_lock(&dev->mode_config.idr_mutex);
lessee = _drm_find_lessee(lessor, arg->lessee_id); @@ -751,6 +791,7 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev,
fail: mutex_unlock(&dev->mode_config.idr_mutex); + drm_master_put(&lessor);
return ret; } diff --git a/include/drm/drm_auth.h b/include/drm/drm_auth.h index 6bf8b2b78991..f99d3417f304 100644 --- a/include/drm/drm_auth.h +++ b/include/drm/drm_auth.h @@ -107,6 +107,7 @@ struct drm_master { };
struct drm_master *drm_master_get(struct drm_master *master); +struct drm_master *drm_file_get_master(struct drm_file *file_priv); void drm_master_put(struct drm_master **master); bool drm_is_current_master(struct drm_file *fpriv);
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h index ca659ece3ee8..42d04607d091 100644 --- a/include/drm/drm_file.h +++ b/include/drm/drm_file.h @@ -233,6 +233,12 @@ struct drm_file { * this only matches &drm_device.master if the master is the currently * active one. * + * When dereferencing this pointer, either hold struct + * &drm_device.master_mutex for the duration of the pointer's use, or + * use drm_file_get_master() if struct &drm_device.master_mutex is not + * currently held and there is no other need to hold it. This prevents + * @master from being freed during use. + * * See also @authentication and @is_master and the :ref:`section on * primary nodes and authentication <drm_primary_node>`. */