[IPV6] fix ipv6_getsockopt_sticky copy_to_user leak

User supplied len < 0 can cause leak of kernel memory.
Use unsigned compare instead.

Signed-off-by: Chris Wright <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv6/ipv6_sockglue.c

···
 		return 0;
 	hdr = opt->hopopt;
 
-	len = min_t(int, len, ipv6_optlen(hdr));
+	len = min_t(unsigned int, len, ipv6_optlen(hdr));
 	if (copy_to_user(optval, hdr, ipv6_optlen(hdr)))
 		return -EFAULT;
 	return len;