[PATCH 6.18 318/333] drm/gud: fix NULL crtc dereference on display disable

Greg Kroah-Hartman
2026-03-17T17:29:05Z

From: Shenghao Yang <me@shenghaoyang.info>

[ Upstream commit 7149be786da012afc6bae293d38f8c1fff1fb90d ]

gud_plane_atomic_update() currently handles both crtc state and
framebuffer updates - the complexity has led to a few accidental
NULL pointer dereferences.

Commit dc2d5ddb193e ("drm/gud: fix NULL fb and crtc dereferences
on USB disconnect") [1] fixed an earlier dereference but planes
can also be disabled in non-hotplug paths (e.g. display disables
via the desktop environment). The drm_dev_enter() call would not
cause an early return in those and 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

Split out crtc handling from gud_plane_atomic_update() into
atomic_enable() and atomic_disable() functions to delegate
crtc state transitioning work to the DRM helpers.

To preserve the gud state commit sequence [2], switch to
the runtime PM version of drm_atomic_helper_commit_tail() which
ensures that crtcs are enabled (hence sending the
GUD_REQ_SET_CONTROLLER_ENABLE and GUD_REQ_SET_DISPLAY_ENABLE
requests) before a framebuffer update is sent.

[1] https://lore.kernel.org/all/20251231055039.44266-1-me@shenghaoyang.info/
[2] https://github.com/notro/gud/wiki/GUD-Protocol#display-state

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202601142159.0v8ilfVs-lkp@intel.com/
Fixes: 73cfd166e045 ("drm/gud: Replace simple display pipe with DRM atomic helpers")
Cc: <stable@vger.kernel.org> # 6.19.x
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Shenghao Yang <me@shenghaoyang.info>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Ruben Wauters <rubenru09@aol.com>
Signed-off-by: Ruben Wauters <rubenru09@aol.com>
Link: https://patch.msgid.link/20260222054551.80864-1-me@shenghaoyang.info
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/gud/gud_drv.c | 9 +++++-
drivers/gpu/drm/gud/gud_internal.h | 4 ++
drivers/gpu/drm/gud/gud_pipe.c | 54 ++++++++++++++++++++++++-------------
3 files changed, 48 insertions(+), 19 deletions(-)

--- a/drivers/gpu/drm/gud/gud_drv.c
+++ b/drivers/gpu/drm/gud/gud_drv.c
@@ -339,7 +339,9 @@ static int gud_stats_debugfs(struct seq_
}

static const struct drm_crtc_helper_funcs gud_crtc_helper_funcs = {
- .atomic_check = drm_crtc_helper_atomic_check
+ .atomic_check = drm_crtc_helper_atomic_check,
+ .atomic_enable = gud_crtc_atomic_enable,
+ .atomic_disable = gud_crtc_atomic_disable,
};

static const struct drm_crtc_funcs gud_crtc_funcs = {
@@ -364,6 +366,10 @@ static const struct drm_plane_funcs gud_
DRM_GEM_SHADOW_PLANE_FUNCS,
};

+static const struct drm_mode_config_helper_funcs gud_mode_config_helpers = {
+ .atomic_commit_tail = drm_atomic_helper_commit_tail_rpm,
+};
+
static const struct drm_mode_config_funcs gud_mode_config_funcs = {
.fb_create = drm_gem_fb_create_with_dirty,
.atomic_check = drm_atomic_helper_check,
@@ -499,6 +505,7 @@ static int gud_probe(struct usb_interfac
drm->mode_config.min_height = le32_to_cpu(desc.min_height);
drm->mode_config.max_height = le32_to_cpu(desc.max_height);
drm->mode_config.funcs = &gud_mode_config_funcs;
+ drm->mode_config.helper_private = &gud_mode_config_helpers;

/* Format init */
formats_dev = devm_kmalloc(dev, GUD_FORMATS_MAX_NUM, GFP_KERNEL);
--- a/drivers/gpu/drm/gud/gud_internal.h
+++ b/drivers/gpu/drm/gud/gud_internal.h
@@ -62,6 +62,10 @@ int gud_usb_set_u8(struct gud_device *gd

void gud_clear_damage(struct gud_device *gdrm);
void gud_flush_work(struct work_struct *work);
+void gud_crtc_atomic_enable(struct drm_crtc *crtc,
+ struct drm_atomic_state *state);
+void gud_crtc_atomic_disable(struct drm_crtc *crtc,
+ struct drm_atomic_state *state);
int gud_plane_atomic_check(struct drm_plane *plane,
struct drm_atomic_state *state);
void gud_plane_atomic_update(struct drm_plane *plane,
--- a/drivers/gpu/drm/gud/gud_pipe.c
+++ b/drivers/gpu/drm/gud/gud_pipe.c
@@ -580,6 +580,39 @@ out:
return ret;
}

+void gud_crtc_atomic_enable(struct drm_crtc *crtc,
+ struct drm_atomic_state *state)
+{
+ struct drm_device *drm = crtc->dev;
+ struct gud_device *gdrm = to_gud_device(drm);
+ int idx;
+
+ if (!drm_dev_enter(drm, &idx))
+ return;
+
+ gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 1);
+ gud_usb_set(gdrm, GUD_REQ_SET_STATE_COMMIT, 0, NULL, 0);
+ gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, 1);
+
+ drm_dev_exit(idx);
+}
+
+void gud_crtc_atomic_disable(struct drm_crtc *crtc,
+ struct drm_atomic_state *state)
+{
+ struct drm_device *drm = crtc->dev;
+ struct gud_device *gdrm = to_gud_device(drm);
+ int idx;
+
+ if (!drm_dev_enter(drm, &idx))
+ return;
+
+ gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, 0);
+ gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 0);
+
+ drm_dev_exit(idx);
+}
+
void gud_plane_atomic_update(struct drm_plane *plane,
struct drm_atomic_state *atomic_state)
{
@@ -607,24 +640,12 @@ void gud_plane_atomic_update(struct drm_
mutex_unlock(&gdrm->damage_lock);
}

- if (!drm_dev_enter(drm, &idx))
+ if (!crtc || !drm_dev_enter(drm, &idx))
return;

- if (!old_state->fb)
- gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 1);
-
- if (fb && (crtc->state->mode_changed || crtc->state->connectors_changed))
- gud_usb_set(gdrm, GUD_REQ_SET_STATE_COMMIT, 0, NULL, 0);
-
- if (crtc->state->active_changed)
- gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, crtc->state->active);
-
- if (!fb)
- goto ctrl_disable;
-
ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
if (ret)
- goto ctrl_disable;
+ goto out;

drm_atomic_helper_damage_iter_init(&iter, old_state, new_state);
drm_atomic_for_each_plane_damage(&iter, &damage)
@@ -632,9 +653,6 @@ void gud_plane_atomic_update(struct drm_

drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);

-ctrl_disable:
- if (!crtc->state->enable)
- gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 0);
-
+out:
drm_dev_exit(idx);
}