af_unix: Move SOCK_PASS{CRED,PIDFD,SEC} to struct sock.

As explained in the next patch, SO_PASSRIGHTS would have a problem
if we assigned a corresponding bit to socket->flags, so it must be
managed in struct sock.

Mixing socket->flags and sk->sk_flags for similar options will look
confusing, and sk->sk_flags does not have enough space on 32bit system.

Also, as mentioned in commit 16e5726 ("af_unix: dont send
SCM_CREDENTIALS by default"), SOCK_PASSCRED and SOCK_PASSPID handling
is known to be slow, and managing the flags in struct socket cannot
avoid that for embryo sockets.

Let's move SOCK_PASS{CRED,PIDFD,SEC} to struct sock.

While at it, other SOCK_XXX flags in net.h are grouped as enum.

Note that assign_bit() was atomic, so the writer side is moved down
after lock_sock() in setsockopt(), but the bit is only read once
in sendmsg() and recvmsg(), so lock_sock() is not needed there.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: q2ven

include/linux/net.h

@@ -36,14 +36,13 @@ struct net;
  * in sock->flags, but moved into sk->sk_wq->flags to be RCU protected.
  * Eventually all flags will be in sk->sk_wq->flags.
  */
-#define SOCKWQ_ASYNC_NOSPACE	0
-#define SOCKWQ_ASYNC_WAITDATA	1
-#define SOCK_NOSPACE		2
-#define SOCK_PASSCRED		3
-#define SOCK_PASSSEC		4
-#define SOCK_SUPPORT_ZC		5
-#define SOCK_CUSTOM_SOCKOPT	6
-#define SOCK_PASSPIDFD		7
+enum socket_flags {
+	SOCKWQ_ASYNC_NOSPACE,
+	SOCKWQ_ASYNC_WAITDATA,
+	SOCK_NOSPACE,
+	SOCK_SUPPORT_ZC,
+	SOCK_CUSTOM_SOCKOPT,
+};
 
 #ifndef ARCH_HAS_SOCKET_TYPES
 /**

include/net/sock.h

@@ -337,6 +337,11 @@ struct sk_filter;
   *	@sk_txtime_deadline_mode: set deadline mode for SO_TXTIME
   *	@sk_txtime_report_errors: set report errors mode for SO_TXTIME
   *	@sk_txtime_unused: unused txtime flags
+  *	@sk_scm_recv_flags: all flags used by scm_recv()
+  *	@sk_scm_credentials: flagged by SO_PASSCRED to recv SCM_CREDENTIALS
+  *	@sk_scm_security: flagged by SO_PASSSEC to recv SCM_SECURITY
+  *	@sk_scm_pidfd: flagged by SO_PASSPIDFD to recv SCM_PIDFD
+  *	@sk_scm_unused: unused flags for scm_recv()
   *	@ns_tracker: tracker for netns reference
   *	@sk_user_frags: xarray of pages the user is holding a reference on.
   *	@sk_owner: reference to the real owner of the socket that calls
@@ -523,7 +528,16 @@ struct sock {
 #endif
 	int			sk_disconnects;
 
-	u8			sk_txrehash;
+	union {
+		u8		sk_txrehash;
+		u8		sk_scm_recv_flags;
+		struct {
+			u8	sk_scm_credentials : 1,
+				sk_scm_security : 1,
+				sk_scm_pidfd : 1,
+				sk_scm_unused : 5;
+		};
+	};
 	u8			sk_clockid;
 	u8			sk_txtime_deadline_mode : 1,
 				sk_txtime_report_errors : 1,

net/core/scm.c

@@ -406,12 +406,12 @@ struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 EXPORT_SYMBOL(scm_fp_dup);
 
 #ifdef CONFIG_SECURITY_NETWORK
-static void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
+static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
 {
 	struct lsm_context ctx;
 	int err;
 
-	if (test_bit(SOCK_PASSSEC, &sock->flags)) {
+	if (sk->sk_scm_security) {
 		err = security_secid_to_secctx(scm->secid, &ctx);
 
 		if (err >= 0) {
@@ -423,16 +423,16 @@ static void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cooki
 	}
 }
 
-static bool scm_has_secdata(struct socket *sock)
+static bool scm_has_secdata(struct sock *sk)
 {
-	return test_bit(SOCK_PASSSEC, &sock->flags);
+	return sk->sk_scm_security;
 }
 #else
-static void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
+static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
 {
 }
 
-static bool scm_has_secdata(struct socket *sock)
+static bool scm_has_secdata(struct sock *sk)
 {
 	return false;
 }
@@ -474,20 +474,19 @@ static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
 		fd_install(pidfd, pidfd_file);
 }
 
-static bool __scm_recv_common(struct socket *sock, struct msghdr *msg,
+static bool __scm_recv_common(struct sock *sk, struct msghdr *msg,
 			      struct scm_cookie *scm, int flags)
 {
 	if (!msg->msg_control) {
-		if (test_bit(SOCK_PASSCRED, &sock->flags) ||
-		    test_bit(SOCK_PASSPIDFD, &sock->flags) ||
-		    scm->fp || scm_has_secdata(sock))
+		if (sk->sk_scm_credentials || sk->sk_scm_pidfd ||
+		    scm->fp || scm_has_secdata(sk))
 			msg->msg_flags |= MSG_CTRUNC;
 
 		scm_destroy(scm);
 		return false;
 	}
 
-	if (test_bit(SOCK_PASSCRED, &sock->flags)) {
+	if (sk->sk_scm_credentials) {
 		struct user_namespace *current_ns = current_user_ns();
 		struct ucred ucreds = {
 			.pid = scm->creds.pid,
@@ -498,7 +497,7 @@ static bool __scm_recv_common(struct socket *sock, struct msghdr *msg,
 		put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
 	}
 
-	scm_passec(sock, msg, scm);
+	scm_passec(sk, msg, scm);
 
 	if (scm->fp)
 		scm_detach_fds(msg, scm);
@@ -509,7 +508,7 @@ static bool __scm_recv_common(struct socket *sock, struct msghdr *msg,
 void scm_recv(struct socket *sock, struct msghdr *msg,
 	      struct scm_cookie *scm, int flags)
 {
-	if (!__scm_recv_common(sock, msg, scm, flags))
+	if (!__scm_recv_common(sock->sk, msg, scm, flags))
 		return;
 
 	scm_destroy_cred(scm);
@@ -519,10 +518,10 @@ EXPORT_SYMBOL(scm_recv);
 void scm_recv_unix(struct socket *sock, struct msghdr *msg,
 		   struct scm_cookie *scm, int flags)
 {
-	if (!__scm_recv_common(sock, msg, scm, flags))
+	if (!__scm_recv_common(sock->sk, msg, scm, flags))
 		return;
 
-	if (test_bit(SOCK_PASSPIDFD, &sock->flags))
+	if (sock->sk->sk_scm_pidfd)
 		scm_pidfd_recv(msg, scm);
 
 	scm_destroy_cred(scm);

net/core/sock.c

@@ -1220,24 +1220,6 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 			return 0;
 		}
 		return -EPERM;
-	case SO_PASSSEC:
-		if (!IS_ENABLED(CONFIG_SECURITY_NETWORK) || 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:
 	case SO_PROTOCOL:
 	case SO_DOMAIN:
@@ -1568,6 +1550,26 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 		sock_valbool_flag(sk, SOCK_SELECT_ERR_QUEUE, valbool);
 		break;
 
+	case SO_PASSCRED:
+		if (sk_may_scm_recv(sk))
+			sk->sk_scm_credentials = valbool;
+		else
+			ret = -EOPNOTSUPP;
+		break;
+
+	case SO_PASSSEC:
+		if (IS_ENABLED(CONFIG_SECURITY_NETWORK) && sk_may_scm_recv(sk))
+			sk->sk_scm_security = valbool;
+		else
+			ret = -EOPNOTSUPP;
+		break;
+
+	case SO_PASSPIDFD:
+		if (sk_is_unix(sk))
+			sk->sk_scm_pidfd = valbool;
+		else
+			ret = -EOPNOTSUPP;
+		break;
 
 	case SO_INCOMING_CPU:
 		reuseport_update_incoming_cpu(sk, val);
@@ -1867,14 +1869,14 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		if (!sk_may_scm_recv(sk))
 			return -EOPNOTSUPP;
 
-		v.val = !!test_bit(SOCK_PASSCRED, &sock->flags);
+		v.val = sk->sk_scm_credentials;
 		break;
 
 	case SO_PASSPIDFD:
 		if (!sk_is_unix(sk))
 			return -EOPNOTSUPP;
 
-		v.val = !!test_bit(SOCK_PASSPIDFD, &sock->flags);
+		v.val = sk->sk_scm_pidfd;
 		break;
 
 	case SO_PEERCRED:
@@ -1974,7 +1976,7 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		if (!IS_ENABLED(CONFIG_SECURITY_NETWORK) || !sk_may_scm_recv(sk))
 			return -EOPNOTSUPP;
 
-		v.val = !!test_bit(SOCK_PASSSEC, &sock->flags);
+		v.val = sk->sk_scm_security;
 		break;
 
 	case SO_PEERSEC:

net/unix/af_unix.c

@@ -767,10 +767,7 @@ static void copy_peercred(struct sock *sk, struct sock *peersk)
 
 static bool unix_may_passcred(const struct sock *sk)
 {
-	struct socket *sock = sk->sk_socket;
-
-	return test_bit(SOCK_PASSCRED, &sock->flags) ||
-		test_bit(SOCK_PASSPIDFD, &sock->flags);
+	return sk->sk_scm_credentials || sk->sk_scm_pidfd;
 }
 
 static int unix_listen(struct socket *sock, int backlog)
@@ -1713,17 +1710,6 @@ static int unix_socketpair(struct socket *socka, struct socket *sockb)
 	return 0;
 }
 
-static void unix_sock_inherit_flags(const struct socket *old,
-				    struct socket *new)
-{
-	if (test_bit(SOCK_PASSCRED, &old->flags))
-		set_bit(SOCK_PASSCRED, &new->flags);
-	if (test_bit(SOCK_PASSPIDFD, &old->flags))
-		set_bit(SOCK_PASSPIDFD, &new->flags);
-	if (test_bit(SOCK_PASSSEC, &old->flags))
-		set_bit(SOCK_PASSSEC, &new->flags);
-}
-
 static int unix_accept(struct socket *sock, struct socket *newsock,
 		       struct proto_accept_arg *arg)
 {
@@ -1760,7 +1746,7 @@ static int unix_accept(struct socket *sock, struct socket *newsock,
 	unix_state_lock(tsk);
 	unix_update_edges(unix_sk(tsk));
 	newsock->state = SS_CONNECTED;
-	unix_sock_inherit_flags(sock, newsock);
+	tsk->sk_scm_recv_flags = READ_ONCE(sk->sk_scm_recv_flags);
 	sock_graft(tsk, newsock);
 	unix_state_unlock(tsk);
 	return 0;