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[2a02:3100:a0f5:8c01:3de3:cd62:aa6f:2fb0]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c249629a901sm383818266b.25.2026.08.22.07.31.21 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 22 Aug 2026 07:31:22 -0700 (PDT) From: Karl Mehltretter To: Maxime Ripard , Dave Stevenson Cc: Karl Mehltretter , =?UTF-8?q?Ma=C3=ADra=20Canal?= , Raspberry Pi Kernel Maintenance , Maarten Lankhorst , Thomas Zimmermann , David Airlie , Simona Vetter , Eric Anholt , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH] drm/vc4: Use managed KMS polling to fix UAF on unbind Date: Sat, 22 Aug 2026 16:31:10 +0200 Message-Id: <20260822143110.68594-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" vc4_kms_load() calls drm_kms_helper_poll_init() but the driver provides no matching drm_kms_helper_poll_fini(). The output poll work stays scheduled after unbind and runs on the freed drm_device: # modprobe vc4; rmmod vc4; sleep 10 BUG: KASAN: slab-use-after-free in delayed_work_timer_fn BUG: KASAN: slab-use-after-free in drm_client_dev_hotplug [drm] Workqueue: events output_poll_execute [drm_kms_helper] Allocated by task 171: __devm_drm_dev_alloc Freed by task 262 (rmmod): drm_dev_put / component_del Use drmm_kms_helper_poll_init() so polling is finalized with the device, as other drivers do. Fixes: c8b75bca92cb ("drm/vc4: Add KMS support for Raspberry Pi.") Assisted-by: Claude:claude-fable-5 Signed-off-by: Karl Mehltretter --- Tested on a Raspberry Pi 400 (BCM2711), v7.2-11658-g26260251022f, with KASAN: report gone, rmmod/insmod loop clean. drivers/gpu/drm/vc4/vc4_kms.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c index b17e73bce384..82a7f2ac4c7e 100644 --- a/drivers/gpu/drm/vc4/vc4_kms.c +++ b/drivers/gpu/drm/vc4/vc4_kms.c @@ -1188,7 +1188,7 @@ int vc4_kms_load(struct drm_device *dev) =20 drm_mode_config_reset(dev); =20 - drm_kms_helper_poll_init(dev); + drmm_kms_helper_poll_init(dev); =20 return 0; } --=20 2.39.5 (Apple Git-154)