Patch "drm/syncobj: Fix use-after-free" has been added to the 5.10-stable tree

[gregkh at linuxfoundation.org]

This is a note to let you know that I've just added the patch titled

    drm/syncobj: Fix use-after-free

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-syncobj-fix-use-after-free.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.


>From a37eef63bc9e16e06361b539e528058146af80ab Mon Sep 17 00:00:00 2001
From: Daniel Vetter <daniel.vetter at ffwll.ch>
Date: Tue, 19 Jan 2021 14:03:18 +0100
Subject: drm/syncobj: Fix use-after-free
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Daniel Vetter <daniel.vetter at ffwll.ch>

commit a37eef63bc9e16e06361b539e528058146af80ab upstream.

While reviewing Christian's annotation patch I noticed that we have a
user-after-free for the WAIT_FOR_SUBMIT case: We drop the syncobj
reference before we've completed the waiting.

Of course usually there's nothing bad happening here since userspace
keeps the reference, but we can't rely on userspace to play nice here!

Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Fixes: bc9c80fe01a2 ("drm/syncobj: use the timeline point in drm_syncobj_find_fence v4")
Reviewed-by: Christian König <christian.koenig at amd.com>
Cc: Christian König <christian.koenig at amd.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Maxime Ripard <mripard at kernel.org>
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: David Airlie <airlied at linux.ie>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: dri-devel at lists.freedesktop.org
Cc: <stable at vger.kernel.org> # v5.2+
Link: https://patchwork.freedesktop.org/patch/msgid/20210119130318.615145-1-daniel.vetter@ffwll.ch
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

---
 drivers/gpu/drm/drm_syncobj.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -388,19 +388,18 @@ int drm_syncobj_find_fence(struct drm_fi
 		return -ENOENT;
 
 	*fence = drm_syncobj_fence_get(syncobj);
-	drm_syncobj_put(syncobj);
 
 	if (*fence) {
 		ret = dma_fence_chain_find_seqno(fence, point);
 		if (!ret)
-			return 0;
+			goto out;
 		dma_fence_put(*fence);
 	} else {
 		ret = -EINVAL;
 	}
 
 	if (!(flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT))
-		return ret;
+		goto out;
 
 	memset(&wait, 0, sizeof(wait));
 	wait.task = current;
@@ -432,6 +431,9 @@ int drm_syncobj_find_fence(struct drm_fi
 	if (wait.node.next)
 		drm_syncobj_remove_wait(syncobj, &wait);
 
+out:
+	drm_syncobj_put(syncobj);
+
 	return ret;
 }
 EXPORT_SYMBOL(drm_syncobj_find_fence);


Patches currently in stable-queue which might be from daniel.vetter at ffwll.ch are

queue-5.10/drm-syncobj-fix-use-after-free.patch
queue-5.10/drm-atomic-put-state-on-error-path.patch