linux-kernel - [PATCH] drm/gud: fix NULL crtc dereference on display disable

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Message-ID: <20260118125044.54467-1-me@shenghaoyang.info>
Date: Sun, 18 Jan 2026 20:50:44 +0800
From: Shenghao Yang <me@...nghaoyang.info>
To: Ruben Wauters <rubenru09@....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>
Cc: dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	Shenghao Yang <me@...nghaoyang.info>,
	stable@...r.kernel.org,
	kernel test robot <lkp@...el.com>,
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: [PATCH] drm/gud: fix NULL crtc dereference on display disable

Commit dc2d5ddb193e ("drm/gud: fix NULL fb and crtc dereferences
on USB disconnect") [1] only fixed the initial NULL crtc dereference
in gud_plane_atomic_update().

However, planes can also be disabled in non-hotplug paths (e.g.
display disables via the DE). The drm_dev_enter() call would not
cause an early return in those and we'll subsequently oops on
dereferencing crtc:

BUG: kernel NULL pointer dereference, address: 00000000000005c8
CPU: 6 UID: 1000 PID: 3473 Comm: kwin_wayland Not tainted 6.18.2-200.vanilla.gud.fc42.x86_64 #1 PREEMPT(lazy)
RIP: 0010:gud_plane_atomic_update+0x148/0x470 [gud]
 <TASK>
 drm_atomic_helper_commit_planes+0x28e/0x310
 drm_atomic_helper_commit_tail+0x2a/0x70
 commit_tail+0xf1/0x150
 drm_atomic_helper_commit+0x13c/0x180
 drm_atomic_commit+0xb1/0xe0
info ? __pfx___drm_printfn_info+0x10/0x10
 drm_mode_atomic_ioctl+0x70f/0x7c0
 ? __pfx_drm_mode_atomic_ioctl+0x10/0x10
 drm_ioctl_kernel+0xae/0x100
 drm_ioctl+0x2a8/0x550
 ? __pfx_drm_mode_atomic_ioctl+0x10/0x10
 __x64_sys_ioctl+0x97/0xe0
 do_syscall_64+0x7e/0x7f0
 ? __ct_user_enter+0x56/0xd0
 ? do_syscall_64+0x158/0x7f0
 ? __ct_user_enter+0x56/0xd0
 ? do_syscall_64+0x158/0x7f0
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Add an early exit and disable the display controller if crtc is NULL.

[1] https://lore.kernel.org/all/20251231055039.44266-1-me@shenghaoyang.info/

Cc: <stable@...r.kernel.org> # 6.18.x
Reported-by: kernel test robot <lkp@...el.com>
Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
Closes: https://lore.kernel.org/r/202601142159.0v8ilfVs-lkp@intel.com/
Fixes: 73cfd166e045 ("drm/gud: Replace simple display pipe with DRM atomic helpers")
Signed-off-by: Shenghao Yang <me@...nghaoyang.info>
---
 drivers/gpu/drm/gud/gud_pipe.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/gud/gud_pipe.c b/drivers/gpu/drm/gud/gud_pipe.c
index 4b77be94348d..a69dee71490f 100644
--- a/drivers/gpu/drm/gud/gud_pipe.c
+++ b/drivers/gpu/drm/gud/gud_pipe.c
@@ -610,6 +610,9 @@ void gud_plane_atomic_update(struct drm_plane *plane,
 	if (!drm_dev_enter(drm, &idx))
 		return;
 
+	if (!crtc)
+		goto ctrl_disable;
+
 	if (!old_state->fb)
 		gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 1);
 
@@ -633,7 +636,7 @@ void gud_plane_atomic_update(struct drm_plane *plane,
 	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
 
 ctrl_disable:
-	if (!crtc->state->enable)
+	if (!crtc || !crtc->state->enable)
 		gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 0);
 
 	drm_dev_exit(idx);
-- 
2.52.0