net: add __sys_accept4_file() helper

This is identical to __sys_accept4(), except it takes a struct file
instead of an fd, and it also allows passing in extra file->f_flags
flags. The latter is done to support masking in O_NONBLOCK without
manipulating the original file flags.

No functional changes in this patch.

Cc: netdev@vger.kernel.org
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/socket.h

@@ -392,6 +392,9 @@ extern int __sys_recvfrom(int fd, void __user *ubuf, size_t size,
 extern int __sys_sendto(int fd, void __user *buff, size_t len,
 			unsigned int flags, struct sockaddr __user *addr,
 			int addr_len);
+extern int __sys_accept4_file(struct file *file, unsigned file_flags,
+			struct sockaddr __user *upeer_sockaddr,
+			 int __user *upeer_addrlen, int flags);
 extern int __sys_accept4(int fd, struct sockaddr __user *upeer_sockaddr,
 			 int __user *upeer_addrlen, int flags);
 extern int __sys_socket(int family, int type, int protocol);

net/socket.c

@@ -1690,24 +1690,13 @@ SYSCALL_DEFINE2(listen, int, fd, int, backlog)
 	return __sys_listen(fd, backlog);
 }
 
-/*
- *	For accept, we attempt to create a new socket, set up the link
- *	with the client, wake up the client, then return the new
- *	connected fd. We collect the address of the connector in kernel
- *	space and move it to user at the very end. This is unclean because
- *	we open the socket then return an error.
- *
- *	1003.1g adds the ability to recvmsg() to query connection pending
- *	status to recvmsg. We need to add that support in a way thats
- *	clean when we restructure accept also.
- */
-
-int __sys_accept4(int fd, struct sockaddr __user *upeer_sockaddr,
-		  int __user *upeer_addrlen, int flags)
+int __sys_accept4_file(struct file *file, unsigned file_flags,
+		       struct sockaddr __user *upeer_sockaddr,
+		       int __user *upeer_addrlen, int flags)
 {
 	struct socket *sock, *newsock;
 	struct file *newfile;
-	int err, len, newfd, fput_needed;
+	int err, len, newfd;
 	struct sockaddr_storage address;
 
 	if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
@@ -1716,14 +1705,14 @@ int __sys_accept4(int fd, struct sockaddr __user *upeer_sockaddr,
 	if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))
 		flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;
 
-	sock = sockfd_lookup_light(fd, &err, &fput_needed);
+	sock = sock_from_file(file, &err);
 	if (!sock)
 		goto out;
 
 	err = -ENFILE;
 	newsock = sock_alloc();
 	if (!newsock)
-		goto out_put;
+		goto out;
 
 	newsock->type = sock->type;
 	newsock->ops = sock->ops;
@@ -1738,20 +1727,21 @@ int __sys_accept4(int fd, struct sockaddr __user *upeer_sockaddr,
 	if (unlikely(newfd < 0)) {
 		err = newfd;
 		sock_release(newsock);
-		goto out_put;
+		goto out;
 	}
 	newfile = sock_alloc_file(newsock, flags, sock->sk->sk_prot_creator->name);
 	if (IS_ERR(newfile)) {
 		err = PTR_ERR(newfile);
 		put_unused_fd(newfd);
-		goto out_put;
+		goto out;
 	}
 
 	err = security_socket_accept(sock, newsock);
 	if (err)
 		goto out_fd;
 
-	err = sock->ops->accept(sock, newsock, sock->file->f_flags, false);
+	err = sock->ops->accept(sock, newsock, sock->file->f_flags | file_flags,
+					false);
 	if (err < 0)
 		goto out_fd;
 
@@ -1772,15 +1762,42 @@ int __sys_accept4(int fd, struct sockaddr __user *upeer_sockaddr,
 
 	fd_install(newfd, newfile);
 	err = newfd;
-
-out_put:
-	fput_light(sock->file, fput_needed);
 out:
 	return err;
 out_fd:
 	fput(newfile);
 	put_unused_fd(newfd);
-	goto out_put;
+	goto out;
+
+}
+
+/*
+ *	For accept, we attempt to create a new socket, set up the link
+ *	with the client, wake up the client, then return the new
+ *	connected fd. We collect the address of the connector in kernel
+ *	space and move it to user at the very end. This is unclean because
+ *	we open the socket then return an error.
+ *
+ *	1003.1g adds the ability to recvmsg() to query connection pending
+ *	status to recvmsg. We need to add that support in a way thats
+ *	clean when we restructure accept also.
+ */
+
+int __sys_accept4(int fd, struct sockaddr __user *upeer_sockaddr,
+		  int __user *upeer_addrlen, int flags)
+{
+	int ret = -EBADF;
+	struct fd f;
+
+	f = fdget(fd);
+	if (f.file) {
+		ret = __sys_accept4_file(f.file, 0, upeer_sockaddr,
+						upeer_addrlen, flags);
+		if (f.flags)
+			fput(f.file);
+	}
+
+	return ret;
 }
 
 SYSCALL_DEFINE4(accept4, int, fd, struct sockaddr __user *, upeer_sockaddr,