Re: [PATCH v1] greybus: authentication: validate CAP response payload size

[Muhammad Bilal <meatuni001@gmail.com>]

On Mon, May 11, 2026 at 03:53:00AM +0000, Greg KH wrote:
> Was this tested on any real greybus devices?

No, I do not have access to real Greybus hardware. The issue was
identified through code review of drivers/staging/greybus/authentication.c.

The vulnerable paths are:

1. payload_size is used in a subtraction without first verifying
   payload_size >= sizeof(*response), which can underflow on short
   responses.

2. The resulting size is passed directly to memcpy() into fixed-size
   UAPI buffers without validating against CAP_CERTIFICATE_MAX_SIZE
   or CAP_SIGNATURE_MAX_SIZE.

A malicious or compromised Greybus endpoint could therefore trigger
an out-of-bounds write through an oversized payload.

The fix adds the missing bounds checks before the memcpy() calls,
which matches common kernel validation patterns.

If testing on real hardware is required before merging, I am happy
to wait.

Thanks,
Muhammad Bilal