Patch "drm/syncobj: Fix use-after-free" has been added to the 5.4-stable tree

Patch "drm/syncobj: Fix use-after-free" has been added to the 5.4-stable tree

[gregkh]

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

    drm/syncobj: Fix use-after-free

to the 5.4-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-5.4 subdirectory.

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


From a37eef63bc9e16e06361b539e528058146af80ab Mon Sep 17 00:00:00 2001
From: Daniel Vetter <daniel.vetter@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@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@intel.com>
Fixes: bc9c80fe01a2 ("drm/syncobj: use the timeline point in drm_syncobj_find_fence v4")
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@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@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
@@ -326,19 +326,18 @@ 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;
@@ -370,6 +369,9 @@ 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@ffwll.ch are

queue-5.4/drm-syncobj-fix-use-after-free.patch
queue-5.4/drm-atomic-put-state-on-error-path.patch
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