| Message ID | 20210722092929.244629-4-desmondcheongzx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm, drm/vmwgfx: fixes and updates related to drm_master | expand |
On 7/22/21 5:29 AM, Desmond Cheong Zhi Xi wrote: > drm_file.master should be protected by either drm_device.master_mutex > or drm_file.master_lookup_lock when being dereferenced. However, > drm_master_get is called on unprotected file_priv->master pointers in > vmw_surface_define_ioctl and vmw_gb_surface_define_internal. > > This is fixed by replacing drm_master_get with drm_file_get_master. > > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> Reviewed-by: Zack Rusin <zackr@vmware.com> Thanks for taking the time to fix this. Apart from the clear logic error, do you happen to know under what circumstances would this be hit? We have someone looking at writing some vmwgfx specific igt tests and I was wondering if I could add this to the list. z
On 23/7/21 3:17 am, Zack Rusin wrote: > On 7/22/21 5:29 AM, Desmond Cheong Zhi Xi wrote: >> drm_file.master should be protected by either drm_device.master_mutex >> or drm_file.master_lookup_lock when being dereferenced. However, >> drm_master_get is called on unprotected file_priv->master pointers in >> vmw_surface_define_ioctl and vmw_gb_surface_define_internal. >> >> This is fixed by replacing drm_master_get with drm_file_get_master. >> >> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> > > Reviewed-by: Zack Rusin <zackr@vmware.com> > > Thanks for taking the time to fix this. Apart from the clear logic > error, do you happen to know under what circumstances would this be hit? > We have someone looking at writing some vmwgfx specific igt tests and I > was wondering if I could add this to the list. > > z Hi Zack, Thanks for the review. For some context, the use-after-free happens when there's a race between accessing the value of drm_file.master, and a call to drm_setmaster_ioctl. If drm_file is not the creator of master, then the ioctl allocates a new master for drm_file and puts the old master. Thus for example, the old value of drm_file.master could be freed in between getting the value of file_priv->master, and the call to drm_master_get. I'm not entirely sure whether this scenario is a good candidate for a test? For further reference, the issue was originally caught by Syzbot here: https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f803 And from the logs it seems that the reproducer set up a race between DRM_IOCTL_GET_UNIQUE and DRM_IOCTL_SET_MASTER. So possibly a race between VMW_CREATE_SURFACE and DRM_IOCTL_SET_MASTER could trigger the same bug. Best wishes, Desmond
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c index 0eba47762bed..5d53a5f9d123 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c @@ -865,7 +865,7 @@ int vmw_surface_define_ioctl(struct drm_device *dev, void *data, user_srf->prime.base.shareable = false; user_srf->prime.base.tfile = NULL; if (drm_is_primary_client(file_priv)) - user_srf->master = drm_master_get(file_priv->master); + user_srf->master = drm_file_get_master(file_priv); /** * From this point, the generic resource management functions @@ -1534,7 +1534,7 @@ vmw_gb_surface_define_internal(struct drm_device *dev, user_srf = container_of(srf, struct vmw_user_surface, srf); if (drm_is_primary_client(file_priv)) - user_srf->master = drm_master_get(file_priv->master); + user_srf->master = drm_file_get_master(file_priv); res = &user_srf->srf.res;
drm_file.master should be protected by either drm_device.master_mutex or drm_file.master_lookup_lock when being dereferenced. However, drm_master_get is called on unprotected file_priv->master pointers in vmw_surface_define_ioctl and vmw_gb_surface_define_internal. This is fixed by replacing drm_master_get with drm_file_get_master. Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> --- drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)