llc: Improve setsockopt() handling of malformed user input

[ Upstream commit 1465036b10be4b8b00eb31c879e86de633ad74c1 ]

copy_from_sockptr() is used incorrectly: return value is the number of
bytes that could not be copied. Since it's deprecated, switch to
copy_safe_from_sockptr().

Note: Keeping the `optlen != sizeof(int)` check as copy_safe_from_sockptr()
by itself would also accept optlen > sizeof(int). Which would allow a more
lenient handling of inputs.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Suggested-by: David Wei <dw@davidwei.uk>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/llc/af_llc.c

@@ -1098,7 +1098,7 @@ static int llc_ui_setsockopt(struct socket *sock, int level, int optname,
 	lock_sock(sk);
 	if (unlikely(level != SOL_LLC || optlen != sizeof(int)))
 		goto out;
-	rc = copy_from_sockptr(&opt, optval, sizeof(opt));
+	rc = copy_safe_from_sockptr(&opt, sizeof(opt), optval, optlen);
 	if (rc)
 		goto out;
 	rc = -EINVAL;