From dd049500e330d76b834e8ba4a57248e7e3556650 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Mon, 1 Oct 2018 17:31:17 +0200 Subject: [PATCH] drm: fix use-after-free read in drm_mode_create_lease_ioctl() fd_install() moves the reference given to it into the file descriptor table of the current process. If the current process is multithreaded, then immediately after fd_install(), another thread can close() the file descriptor and cause the file's resources to be cleaned up. Since the reference to "lessee" is held by the file, we must not access "lessee" after the fd_install() call. As far as I can tell, to reach this codepath, the caller must have an open file descriptor to a DRI device in master mode. I'm not sure what the requirements for that are. Signed-off-by: Jann Horn Fixes: bba0f602c30a ("drm: Add four ioctls for managing drm mode object leases [v7]") Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20181001153117.216923-1-jannh@google.com --- drivers/gpu/drm/drm_lease.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c index b54fb78a283c6..b82da96ded5c8 100644 --- a/drivers/gpu/drm/drm_lease.c +++ b/drivers/gpu/drm/drm_lease.c @@ -566,14 +566,14 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, lessee_priv->is_master = 1; lessee_priv->authenticated = 1; - /* Hook up the fd */ - fd_install(fd, lessee_file); - /* Pass fd back to userspace */ DRM_DEBUG_LEASE("Returning fd %d id %d\n", fd, lessee->lessee_id); cl->fd = fd; cl->lessee_id = lessee->lessee_id; + /* Hook up the fd */ + fd_install(fd, lessee_file); + DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n"); return 0; -- 2.39.5