unexport sock_map_fd(), switch to sock_alloc_file()

Both modular callers of sock_map_fd() had been buggy; sctp one leaks
descriptor and file if copy_to_user() fails, 9p one shouldn't be
exposing file in the descriptor table at all.

Switch both to sock_alloc_file(), export it, unexport sock_map_fd() and
make it static.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/net.h

@@ -65,6 +65,7 @@ typedef enum {
 struct poll_table_struct;
 struct pipe_inode_info;
 struct inode;
+struct file;
 struct net;
 
 #define SOCK_ASYNC_NOSPACE	0
@@ -246,7 +247,7 @@ extern int   	     sock_sendmsg(struct socket *sock, struct msghdr *msg,
 				  size_t len);
 extern int	     sock_recvmsg(struct socket *sock, struct msghdr *msg,
 				  size_t size, int flags);
-extern int 	     sock_map_fd(struct socket *sock, int flags);
+extern struct file  *sock_alloc_file(struct socket *sock, int flags);
 extern struct socket *sockfd_lookup(int fd, int *err);
 extern struct socket *sock_from_file(struct file *file, int *err);
 #define		     sockfd_put(sock) fput(sock->file)

net/9p/trans_fd.c

@@ -793,30 +793,28 @@ static int p9_fd_open(struct p9_client *client, int rfd, int wfd)
 static int p9_socket_open(struct p9_client *client, struct socket *csocket)
 {
 	struct p9_trans_fd *p;
-	int ret, fd;
+	struct file *file;
+	int ret;
 
 	p = kmalloc(sizeof(struct p9_trans_fd), GFP_KERNEL);
 	if (!p)
 		return -ENOMEM;
 
 	csocket->sk->sk_allocation = GFP_NOIO;
-	fd = sock_map_fd(csocket, 0);
-	if (fd < 0) {
+	file = sock_alloc_file(csocket, 0);
+	if (IS_ERR(file)) {
 		pr_err("%s (%d): failed to map fd\n",
 		       __func__, task_pid_nr(current));
 		sock_release(csocket);
 		kfree(p);
-		return fd;
+		return PTR_ERR(file);
 	}
 
-	get_file(csocket->file);
-	get_file(csocket->file);
-	p->wr = p->rd = csocket->file;
+	get_file(file);
+	p->wr = p->rd = file;
 	client->trans = p;
 	client->status = Connected;
 
-	sys_close(fd);	/* still racy */
-
 	p->rd->f_flags |= O_NONBLOCK;
 
 	p->conn = p9_conn_create(client);

net/sctp/socket.c

@@ -70,6 +70,7 @@
 #include <linux/init.h>
 #include <linux/crypto.h>
 #include <linux/slab.h>
+#include <linux/file.h>
 
 #include <net/ip.h>
 #include <net/icmp.h>
@@ -4276,6 +4277,7 @@ static int sctp_getsockopt_peeloff(struct sock *sk, int len, char __user *optval
 {
 	sctp_peeloff_arg_t peeloff;
 	struct socket *newsock;
+	struct file *newfile;
 	int retval = 0;
 
 	if (len < sizeof(sctp_peeloff_arg_t))
@@ -4289,22 +4291,35 @@ static int sctp_getsockopt_peeloff(struct sock *sk, int len, char __user *optval
 		goto out;
 
 	/* Map the socket to an unused fd that can be returned to the user.  */
-	retval = sock_map_fd(newsock, 0);
+	retval = get_unused_fd();
 	if (retval < 0) {
 		sock_release(newsock);
 		goto out;
 	}
 
+	newfile = sock_alloc_file(newsock, 0);
+	if (unlikely(IS_ERR(newfile))) {
+		put_unused_fd(retval);
+		sock_release(newsock);
+		return PTR_ERR(newfile);
+	}
+
 	SCTP_DEBUG_PRINTK("%s: sk: %p newsk: %p sd: %d\n",
 			  __func__, sk, newsock->sk, retval);
 
 	/* Return the fd mapped to the new socket.  */
+	if (put_user(len, optlen)) {
+		fput(newfile);
+		put_unused_fd(retval);
+		return -EFAULT;
+	}
 	peeloff.sd = retval;
-	if (put_user(len, optlen))
+	if (copy_to_user(optval, &peeloff, len)) {
+		fput(newfile);
+		put_unused_fd(retval);
 		return -EFAULT;
-	if (copy_to_user(optval, &peeloff, len))
-		retval = -EFAULT;
-
+	}
+	fd_install(retval, newfile);
 out:
 	return retval;
 }

net/socket.c

@@ -346,7 +346,7 @@ static struct file_system_type sock_fs_type = {
  *	but we take care of internal coherence yet.
  */
 
-static struct file *sock_alloc_file(struct socket *sock, int flags)
+struct file *sock_alloc_file(struct socket *sock, int flags)
 {
 	struct qstr name = { .name = "" };
 	struct path path;
@@ -375,8 +375,9 @@ static struct file *sock_alloc_file(struct socket *sock, int flags)
 	file->private_data = sock;
 	return file;
 }
+EXPORT_SYMBOL(sock_alloc_file);
 
-int sock_map_fd(struct socket *sock, int flags)
+static int sock_map_fd(struct socket *sock, int flags)
 {
 	struct file *newfile;
 	int fd = get_unused_fd_flags(flags);
@@ -392,7 +393,6 @@ int sock_map_fd(struct socket *sock, int flags)
 	put_unused_fd(fd);
 	return PTR_ERR(newfile);
 }
-EXPORT_SYMBOL(sock_map_fd);
 
 struct socket *sock_from_file(struct file *file, int *err)
 {