wifi: iwlwifi: pcie: Fix integer overflow in iwl_write_to_user_buf

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

wifi: iwlwifi: pcie: Fix integer overflow in iwl_write_to_user_buf

An integer overflow occurs in the iwl_write_to_user_buf() function,
which is called by the iwl_dbgfs_monitor_data_read() function.

static bool iwl_write_to_user_buf(char __user *user_buf, ssize_t count,
void *buf, ssize_t *size,
ssize_t *bytes_copied)
{
int buf_size_left = count - *bytes_copied;

buf_size_left = buf_size_left - (buf_size_left % sizeof(u32));
if (*size > buf_size_left)
*size = buf_size_left;

If the user passes a SIZE_MAX value to the "ssize_t count" parameter,
the ssize_t count parameter is assigned to "int buf_size_left".
Then compare "*size" with "buf_size_left" . Here, "buf_size_left" is a
negative number, so "*size" is assigned "buf_size_left" and goes into
the third argument of the copy_to_user function, causing a heap overflow.

This is not a security vulnerability because iwl_dbgfs_monitor_data_read()
is a debugfs operation with 0400 privileges.