[PATCH v2 net-next 5/9] net: Restrict SO_PASS{CRED,PIDFD,SEC} to AF_{UNIX,NETLINK,BLUETOOTH}.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

SCM_CREDENTIALS and SCM_SECURITY can be recv()ed by calling
scm_recv() or scm_recv_unix(), and SCM_PIDFD is only used by
scm_recv_unix().

scm_recv() is called from AF_NETLINK and AF_BLUETOOTH.

scm_recv_unix() is literally called from AF_UNIX.

Let's restrict SO_PASSCRED and SO_PASSSEC to such sockets and
SO_PASSPIDFD to AF_UNIX only.

Later, SOCK_PASS{CRED,PIDFD,SEC} will be moved to struct sock
and united with another field, so we set 0 explicitly in
getsockopt().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/net/sock.h | 14 +++++++++++++-
 net/core/sock.c    | 24 +++++++++++++++++++++---
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index f0fabb9fd28a..af0719ba331f 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2772,9 +2772,14 @@ static inline bool sk_is_udp(const struct sock *sk)
 	       sk->sk_protocol == IPPROTO_UDP;
 }
 
+static inline bool sk_is_unix(const struct sock *sk)
+{
+	return sk->sk_family == AF_UNIX;
+}
+
 static inline bool sk_is_stream_unix(const struct sock *sk)
 {
-	return sk->sk_family == AF_UNIX && sk->sk_type == SOCK_STREAM;
+	return sk_is_unix(sk) && sk->sk_type == SOCK_STREAM;
 }
 
 static inline bool sk_is_vsock(const struct sock *sk)
@@ -2782,6 +2787,13 @@ static inline bool sk_is_vsock(const struct sock *sk)
 	return sk->sk_family == AF_VSOCK;
 }
 
+static inline bool sk_may_scm_recv(const struct sock *sk)
+{
+	return (IS_ENABLED(CONFIG_UNIX) && sk->sk_family == AF_UNIX) ||
+		sk->sk_family == AF_NETLINK ||
+		(IS_ENABLED(CONFIG_BT) && sk->sk_family == AF_BLUETOOTH);
+}
+
 /**
  * sk_eat_skb - Release a skb if it is no longer needed
  * @sk: socket to eat this skb from
diff --git a/net/core/sock.c b/net/core/sock.c
index 5c84a608ddd7..1ab59efbafc5 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1221,12 +1221,21 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 		}
 		return -EPERM;
 	case SO_PASSSEC:
+		if (!sk_may_scm_recv(sk))
+			return -EOPNOTSUPP;
+
 		assign_bit(SOCK_PASSSEC, &sock->flags, valbool);
 		return 0;
 	case SO_PASSCRED:
+		if (!sk_may_scm_recv(sk))
+			return -EOPNOTSUPP;
+
 		assign_bit(SOCK_PASSCRED, &sock->flags, valbool);
 		return 0;
 	case SO_PASSPIDFD:
+		if (!sk_is_unix(sk))
+			return -EOPNOTSUPP;
+
 		assign_bit(SOCK_PASSPIDFD, &sock->flags, valbool);
 		return 0;
 	case SO_TYPE:
@@ -1855,11 +1864,17 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		break;
 
 	case SO_PASSCRED:
-		v.val = !!test_bit(SOCK_PASSCRED, &sock->flags);
+		if (sk_may_scm_recv(sk))
+			v.val = !!test_bit(SOCK_PASSCRED, &sock->flags);
+		else
+			v.val = 0;
 		break;
 
 	case SO_PASSPIDFD:
-		v.val = !!test_bit(SOCK_PASSPIDFD, &sock->flags);
+		if (sk_is_unix(sk))
+			v.val = !!test_bit(SOCK_PASSPIDFD, &sock->flags);
+		else
+			v.val = 0;
 		break;
 
 	case SO_PEERCRED:
@@ -1956,7 +1971,10 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		break;
 
 	case SO_PASSSEC:
-		v.val = !!test_bit(SOCK_PASSSEC, &sock->flags);
+		if (sk_may_scm_recv(sk))
+			v.val = !!test_bit(SOCK_PASSSEC, &sock->flags);
+		else
+			v.val = 0;
 		break;
 
 	case SO_PEERSEC:
-- 
2.49.0