__issei_ham_process_ham_rsp() dispatches on hdr->cmd before the message
length is validated. The length comes from the firmware-owned DMA header
read in issei_dma_read(), which only bounds it from above, so firmware
sending a short bus message reaches the dispatch with less than
sizeof(struct ham_bus_message) bytes available.

For a zero-length message kmemdup() returns ZERO_SIZE_PTR, which passes
the NULL check in issei_dma_read(), and the dispatch dereferences it. A
length of one to three bytes gives a slab out-of-bounds read instead.

Reject bus messages shorter than the header before touching it, the way
the individual response handlers already validate their own length.

Fixes: 7bd4b9991db20 ("issei: implement main thread and ham messages")
Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
Link: https://patch.msgid.link/20260731025952.3505287-1-lilinmao@kylinos.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Introduce the main thread and HECI Active Management (HAM)
message handling for the ISSEI (Intel Silicon Security Engine
Interface) subsystem.
The main thread is responsible for managing the reset flow and
processing messages, while the HAM message handling is crucial
for initializing communication with the firmware and managing
clients.

With this implementation, the ISSEI driver is capable of performing
the required initialization and management of communication between
the host and the firmware.

Reviewed-by: Karol Wachowski <karol.wachowski@linux.intel.com>
Co-developed-by: Vitaly Lubart <lubvital@gmail.com>
Signed-off-by: Vitaly Lubart <lubvital@gmail.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Link: https://patch.msgid.link/20260513-issei-for-upstream-v1-3-f590038678f9@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>