[PATCH 6.12.y] media: ipu-bridge: Fix use-after-free in IVSC error path

[Sasha Levin <sashal@kernel.org>]

From: Yibo Tan <lhfff@tju.edu.cn>

[ Upstream commit 3d42d1c82717f0853379b516a7fab54b636e09cc ]

ipu_bridge_get_ivsc_acpi_dev() returns an ACPI device with a reference
held. If no matching CSI device is found, ipu_bridge_check_ivsc_dev()
drops that reference before passing the device to dev_err(). Concurrent
CSI device and ACPI namespace removal can drop the other references,
making this the final put. dev_err() then reads the freed struct
acpi_device and its kobject name.

This was reproduced without kprobes by racing normal CSI platform-device
unregistration and ACPI configfs table removal against the production
ipu_bridge_init() entry. KASAN reported the final free through
device_release(), followed by invalid reads through _dev_err().

Emit the error message while the lookup reference is still held, then
drop the reference as before.

Source reproducers and vulnerable/fixed serial logs, with only the build
hostname redacted, are available at:
https://github.com/kimaiden1984-boop/linux-ipu-bridge-acpi-uaf-reproducer

The fixed target builds with W=1 on x86-64. This was not tested on
physical IPU hardware. The tests establish runtime reachability but do
not measure occurrence frequency on shipping systems or establish
exploitability.

Fixes: c66821f381ae ("media: pci: intel: Add IVSC support for IPU bridge driver")
Cc: stable@vger.kernel.org
Assisted-by: Codex:GPT-5
Signed-off-by: Yibo Tan <lhfff@tju.edu.cn>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
[ sashal: adjusted context for the error message that mentions only MEI instead of MEI or CVS ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/media/pci/intel/ipu-bridge.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/pci/intel/ipu-bridge.c b/drivers/media/pci/intel/ipu-bridge.c
index 4e921c7516293..faa7e538bc2f2 100644
--- a/drivers/media/pci/intel/ipu-bridge.c
+++ b/drivers/media/pci/intel/ipu-bridge.c
@@ -191,8 +191,8 @@ static int ipu_bridge_check_ivsc_dev(struct ipu_sensor *sensor,
 	if (adev) {
 		csi_dev = ipu_bridge_get_ivsc_csi_dev(adev);
 		if (!csi_dev) {
-			acpi_dev_put(adev);
 			dev_err(ADEV_DEV(adev), "Failed to find MEI CSI dev\n");
+			acpi_dev_put(adev);
 			return -ENODEV;
 		}
 
-- 
2.53.0