On Tue, Jun 29, 2021 at 11:37:06AM +0800, Desmond Cheong Zhi Xi wrote: > Currently, direct copies of drm_file->master pointers should be > protected by drm_device.master_mutex when being dereferenced. This is > because drm_file->master is not invariant for the lifetime of > drm_file. If drm_file is not the creator of master, then > drm_file->is_master is false, and a call to drm_setmaster_ioctl will > invoke drm_new_set_master, which then allocates a new master for > drm_file and puts the old master. > > Thus, without holding drm_device.master_mutex, the old value of > drm_file->master could be freed while it is being used by another > concurrent process. > > In drm_lease.c, there are multiple instances where drm_file->master is > accessed and dereferenced while drm_device.master_mutex is not > held. This makes drm_lease.c vulnerable to use-after-free bugs. > > We address this issue in 3 ways: > > 1. Clarify in the kerneldoc that drm_file->master is protected by > drm_device.master_mutex. > > 2. Add a new drm_file_get_master() function that calls drm_master_get > on drm_file->master while holding on to drm_device.master_mutex. Since > drm_master_get increments the reference count of master, this > prevents master from being freed until we unreference it with > drm_master_put. > > 3. 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@xxxxxxxx> > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx> Series looks very nice, let's see what intel-gfx-ci says. You should get a mail, but results are also here: https://patchwork.freedesktop.org/series/91969/#rev2 One tiny comment below. > --- > drivers/gpu/drm/drm_auth.c | 25 ++++++++++++ > drivers/gpu/drm/drm_lease.c | 77 +++++++++++++++++++++++++++---------- > include/drm/drm_auth.h | 1 + > include/drm/drm_file.h | 15 ++++++-- > 4 files changed, 95 insertions(+), 23 deletions(-) > > diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c > index ab1863c5a5a0..c36a0b72be26 100644 > --- a/drivers/gpu/drm/drm_auth.c > +++ b/drivers/gpu/drm/drm_auth.c > @@ -384,6 +384,31 @@ 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; > + > + mutex_lock(&file_priv->minor->dev->master_mutex); > + if (!file_priv->master) > + goto unlock; > + master = drm_master_get(file_priv->master); > + > +unlock: > + mutex_unlock(&file_priv->minor->dev->master_mutex); > + 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 00fb433bcef1..cdcc87fa9685 100644 > --- a/drivers/gpu/drm/drm_lease.c > +++ b/drivers/gpu/drm/drm_lease.c > @@ -106,10 +106,19 @@ 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 == NULL) > + return true; > + ret = _drm_lease_held_master(master, id); > + drm_master_put(&master); > + > + return ret; > } > > /** > @@ -128,13 +137,20 @@ 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 == NULL) > + return true; > + if (!master->lessor) { > + drm_master_put(&master); > + return true; > + } > mutex_lock(&master->dev->mode_config.idr_mutex); > ret = _drm_lease_held_master(master, id); > mutex_unlock(&master->dev->mode_config.idr_mutex); > + drm_master_put(&master); > return ret; > } > > @@ -154,10 +170,16 @@ 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 == NULL) > + return crtcs_in; > + if (!master->lessor) { > + drm_master_put(&master); > + return crtcs_in; > + } > dev = master->dev; > > count_in = count_out = 0; > @@ -176,6 +198,7 @@ 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); > + drm_master_put(&master); > return crtcs_out; > } > > @@ -489,7 +512,7 @@ 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; > @@ -501,12 +524,6 @@ 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"); > @@ -518,12 +535,22 @@ 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); > > @@ -534,14 +561,15 @@ 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"); > @@ -577,6 +605,7 @@ 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; > > @@ -586,6 +615,8 @@ 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; > } > @@ -608,7 +639,7 @@ 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; > > @@ -619,6 +650,7 @@ 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); > @@ -642,6 +674,7 @@ 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; > } > @@ -661,7 +694,7 @@ 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; > @@ -675,6 +708,7 @@ 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); > @@ -702,6 +736,7 @@ 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; > } > @@ -720,7 +755,7 @@ 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; > > @@ -730,6 +765,7 @@ 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); > @@ -750,6 +786,7 @@ 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 b81b3bfb08c8..e9931fca4ab7 100644 > --- a/include/drm/drm_file.h > +++ b/include/drm/drm_file.h > @@ -226,9 +226,18 @@ struct drm_file { > /** > * @master: > * > - * Master this node is currently associated with. Only relevant if > - * drm_is_primary_client() returns true. Note that this only > - * matches &drm_device.master if the master is the currently active one. > + * Master this node is currently associated with. Protected by struct > + * &drm_device.master_mutex. > + * > + * Only relevant if drm_is_primary_client() returns true. Note that > + * this only matches &drm_device.master if the master is the currently > + * active one. > + * > + * When obtaining a copy of this pointer, it is recommended to either I found this a bit confusing, since I generally don't think of dereferencing the pointer as "taking a copy". That's more for the entire datastructure when you have a memcpy() call, or kmemdup() or something like that. Also "it is recommended" is a bit weak if you get a use-after-free if you dont :-) So instead "When dererencing this pointer either hold ... or use drm_file_get_master() ...." Cheers, Daniel > + * hold struct &drm_device.master_mutex for the duration of the > + * pointer's use, or to 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>`. > -- > 2.25.1 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
