[PATCH] usb: typec: ucsi: acpi: don't dereference a missing ACPI companion

[Yogesh Gaur <yogeshgaur.83@gmail.com>]

ucsi_acpi_probe() reads adev->dep_unmet before it has established that
the platform device has an ACPI companion at all:

	struct acpi_device *adev = ACPI_COMPANION(&pdev->dev);
	...
	if (adev->dep_unmet)
		return -EPROBE_DEFER;

ACPI_COMPANION() returns NULL for a platform device that was not
enumerated from an ACPI node. The driver only advertises an
acpi_match_table, so the bus-match path cannot reach the probe with a
NULL companion -- but the probe is also reachable from sysfs, and that
path does not consult a match table. Writing a device name to
/sys/bus/platform/drivers/ucsi_acpi/bind goes straight to
device_driver_attach() -> really_probe(), so any platform device in the
system can be handed to ucsi_acpi_probe(), including the many that have
no ACPI companion:

  Oops: general protection fault, probably for non-canonical address
        0xdffffc00000000fc: 0000 [#1] SMP KASAN PTI
  KASAN: null-ptr-deref in range [0x00000000000007e0-0x00000000000007e7]
  RIP: 0010:ucsi_acpi_probe+0x6c/0x4b0 drivers/usb/typec/ucsi/ucsi_acpi.c:199
  Call Trace:
   platform_probe+0xf9/0x190 drivers/base/platform.c:1507
   really_probe+0x254/0xae0 drivers/base/dd.c:706
   __driver_probe_device+0x1e8/0x360 drivers/base/dd.c:868
   device_driver_attach+0xe0/0x1d0 drivers/base/dd.c:1203
   bind_store+0x1d3/0x220 drivers/base/bus.c:267
   kernfs_fop_write_iter+0x3a5/0x540 fs/kernfs/file.c:345
   vfs_write+0x61e/0xbb0 fs/read_write.c:687

The faulting address is the dep_unmet member read off a NULL
struct acpi_device.

Bail out with -ENODEV when there is no companion. Every other use of
the device in this probe goes through ACPI_HANDLE(), which tolerates a
missing companion and would just have failed later with a less useful
error, so rejecting the bind up front is both the smallest fix and the
honest answer: this driver cannot drive a non-ACPI device.

This is the only unchecked ACPI_COMPANION() in drivers/usb/typec/.

Fixes: 1f3546ff3f0a ("usb: typec: ucsi: acpi: Check the _DEP dependencies")
Reported-by: syzbot+e7aa19176573a6992617@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e7aa19176573a6992617
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Yogesh Gaur <yogeshgaur.83@gmail.com>
---
 drivers/usb/typec/ucsi/ucsi_acpi.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/typec/ucsi/ucsi_acpi.c b/drivers/usb/typec/ucsi/ucsi_acpi.c
index 18286d3e9cc5..9fe4ba43afea 100644
--- a/drivers/usb/typec/ucsi/ucsi_acpi.c
+++ b/drivers/usb/typec/ucsi/ucsi_acpi.c
@@ -196,6 +196,9 @@ static int ucsi_acpi_probe(struct platform_device *pdev)
 	acpi_status status;
 	int ret;
 
+	if (!adev)
+		return -ENODEV;
+
 	if (adev->dep_unmet)
 		return -EPROBE_DEFER;
 
-- 
2.55.0.windows.5