linux-kernel - Re: [syzbot] [dri?] KASAN: slab-use-after-free Read in drm_atomic_helper_wait_for

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Message-ID: <20240214070145.360-1-hdanton@sina.com>
Date: Wed, 14 Feb 2024 15:01:44 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+0f999d26a4fd79c3a23b@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [dri?] KASAN: slab-use-after-free Read in drm_atomic_helper_wait_for_vblanks (2)

On Tue, 13 Feb 2024 06:08:15 -0800
> HEAD commit:    c664e16bb1ba Merge tag 'docs-6.8-fixes2' of git://git.lwn...
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11fcdba2180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  master

--- x/drivers/gpu/drm/drm_client_modeset.c
+++ y/drivers/gpu/drm/drm_client_modeset.c
@@ -987,6 +987,7 @@ static int drm_client_modeset_commit_ato
 	struct drm_mode_set *mode_set;
 	int ret;
 
+retry:
 	drm_modeset_acquire_init(&ctx, 0);
 
 	state = drm_atomic_state_alloc(dev);
@@ -996,7 +997,6 @@ static int drm_client_modeset_commit_ato
 	}
 
 	state->acquire_ctx = &ctx;
-retry:
 	drm_for_each_plane(plane, dev) {
 		struct drm_plane_state *plane_state;
 
@@ -1051,21 +1051,15 @@ retry:
 		ret = drm_atomic_commit(state);
 
 out_state:
-	if (ret == -EDEADLK)
-		goto backoff;
-
 	drm_atomic_state_put(state);
 out_ctx:
 	drm_modeset_drop_locks(&ctx);
 	drm_modeset_acquire_fini(&ctx);
 
-	return ret;
-
-backoff:
-	drm_atomic_state_clear(state);
-	drm_modeset_backoff(&ctx);
+	if (ret == -EDEADLK)
+		goto retry;
 
-	goto retry;
+	return ret;
 }
 
 static int drm_client_modeset_commit_legacy(struct drm_client_dev *client)
--