linux-kernel - [PATCH 2/2] drm/atmel-hlcdc: fix use-after-free of drm_crtc

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Message-ID: <20251024-lcd_fixes_mainlining-v1-2-79b615130dc3@microchip.com>
Date: Fri, 24 Oct 2025 18:14:53 +0200
From: Ludovic Desroches <ludovic.desroches@...rochip.com>
To: Manikandan Muralidharan <manikandan.m@...rochip.com>, "Dharma
 Balasubiramani" <dharma.b@...rochip.com>, Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>, Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>, Claudiu Beznea
	<claudiu.beznea@...on.dev>
CC: <dri-devel@...ts.freedesktop.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Ludovic Desroches
	<ludovic.desroches@...rochip.com>
Subject: [PATCH 2/2] drm/atmel-hlcdc: fix use-after-free of drm_crtc_commit
 after release

The atmel_hlcdc_plane_atomic_duplicate_state() callback was copying
the atmel_hlcdc_plane state structure without properly duplicating the
drm_plane_state. In particular, state->commit remained set to the old
state commit, which can lead to a use-after-free in the next
drm_atomic_commit() call.

Fix this by calling
__drm_atomic_helper_duplicate_plane_state(), which correctly clones
the base drm_plane_state (including the ->commit pointer).

It has been seen when closing and re-opening the device node while
another DRM client (e.g. fbdev) is still attached:

=============================================================================
BUG kmalloc-64 (Not tainted): Poison overwritten
-----------------------------------------------------------------------------

0xc611b344-0xc611b344 @offset=836. First byte 0x6a instead of 0x6b
FIX kmalloc-64: Restoring Poison 0xc611b344-0xc611b344=0x6b
Allocated in drm_atomic_helper_setup_commit+0x1e8/0x7bc age=178 cpu=0
pid=29
 drm_atomic_helper_setup_commit+0x1e8/0x7bc
 drm_atomic_helper_commit+0x3c/0x15c
 drm_atomic_commit+0xc0/0xf4
 drm_framebuffer_remove+0x4cc/0x5a8
 drm_mode_rmfb_work_fn+0x6c/0x80
 process_one_work+0x12c/0x2cc
 worker_thread+0x2a8/0x400
 kthread+0xc0/0xdc
 ret_from_fork+0x14/0x28
Freed in drm_atomic_helper_commit_hw_done+0x100/0x150 age=8 cpu=0
pid=169
 drm_atomic_helper_commit_hw_done+0x100/0x150
 drm_atomic_helper_commit_tail+0x64/0x8c
 commit_tail+0x168/0x18c
 drm_atomic_helper_commit+0x138/0x15c
 drm_atomic_commit+0xc0/0xf4
 drm_atomic_helper_set_config+0x84/0xb8
 drm_mode_setcrtc+0x32c/0x810
 drm_ioctl+0x20c/0x488
 sys_ioctl+0x14c/0xc20
 ret_fast_syscall+0x0/0x54
Slab 0xef8bc360 objects=21 used=16 fp=0xc611b7c0
flags=0x200(workingset|zone=0)
Object 0xc611b340 @offset=832 fp=0xc611b7c0

Signed-off-by: Ludovic Desroches <ludovic.desroches@...rochip.com>
Reviewed-by: Manikandan Muralidharan <manikandan.m@...rochip.com>
---
 drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
index 0e38587b868d5b5375fcaa5c0508e8e5690d8ff8..91df1273eac71512109a822000448d7641171dca 100644
--- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
+++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
@@ -1196,8 +1196,7 @@ atmel_hlcdc_plane_atomic_duplicate_state(struct drm_plane *p)
 		return NULL;
 	}

-	if (copy->base.fb)
-		drm_framebuffer_get(copy->base.fb);
+	__drm_atomic_helper_plane_duplicate_state(p, &copy->base);

 	return &copy->base;
 }

-- 
2.51.0