phonet: pep: do not write beyond optlen in getsockopt

In the Linux kernel, the following vulnerability has been resolved: phonet: pep: do not write beyond optlen in getsockopt pep_getsockopt() clamps the reported length to the caller's buffer with min_t(), but then stores the value with put_user(val, (int __user *) optval), which always writes sizeof(int) bytes. A getsockopt() call with an optlen smaller than sizeof(int) thus reports the clamped length yet writes a full int, one to three bytes past the user buffer. Write the value with copy_to_user() bounded by len, so at most optlen bytes are copied, matching the length reported back to userspace.

Where it's fixed