ibmasm: fix OOB reads in command_file_write due to missing size checks

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

ibmasm: fix OOB reads in command_file_write due to missing size checks

The command_file_write() handler allocates a kernel buffer of exactly

count bytes and copies user data into it, but does not validate the

buffer against the dot command protocol before passing it to

get_dot_command_size() and get_dot_command_timeout().

Since both the allocation size (count) and the header fields (command_size,

data_size) are independently user-controlled, an attacker can cause

get_dot_command_size() to return a value exceeding the allocation,

triggering OOB reads in get_dot_command_timeout() and an out-of-bounds

memcpy_toio() that leaks kernel heap memory to the service processor.

Fix with two guards: reject writes smaller than sizeof(struct

dot_command_header) before allocation, then after copying user data

reject commands where the buffer is smaller than the total size declared

by the header (sizeof(header) + command_size + data_size). This ensures

all subsequent header and payload field accesses stay within the buffer.