AZL-94401

In the Linux kernel, the following vulnerability has been resolved:

Input: ims-pcu - fix heap-buffer-overflow in imspcuprocess_data()

The ims_pcu_process_data() processes incoming URB data byte by byte. However, it fails to check if the read_pos index exceeds IMSPCUBUF_SIZE.

If a malicious USB device sends a packet larger than IMSPCUBUF_SIZE, read_pos will increment indefinitely. Moreover, since read_pos is located immediately after read_buf, the attacker can overwrite read_pos itself to arbitrarily control the index.

This manipulated read_pos is subsequently used in ims_pcu_handle_response() to copy data into cmd_buf, leading to a heap buffer overflow.

Specifically, an attacker can overwrite the cmd_done.wait.head located at offset 136 relative to cmd_buf in the ims_pcu_handle_response(). Consequently, when the driver calls complete(&pcu->cmd_done), it triggers a control flow hijack by using the manipulated pointer.

Fix this by adding a bounds check for read_pos before writing to read_buf. If the packet is too long, discard it, log a warning, and reset the parser state.

[dtor: factor out resetting packet state, reset checksum as well]