[PATCH RFC POC 34/50] sctp: install the peeloff descriptor when the syscall returns

[Christian Brauner]

Rely on the fd exit path machinery.

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 net/sctp/socket.c | 78 +++++++++++++++++++++----------------------------------
 1 file changed, 29 insertions(+), 49 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index c7b9e325ec1c..b75c50af8c16 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -5744,46 +5744,41 @@ static int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id,
 }
 
 static int sctp_getsockopt_peeloff_common(struct sock *sk, sctp_peeloff_arg_t *peeloff,
-					  struct file **newfile, unsigned flags)
+					  unsigned flags)
 {
 	struct socket *newsock;
+	struct file *newfile;
+	const struct fd_slot *fd;
 	int retval;
 
 	retval = sctp_do_peeloff(sk, peeloff->associd, &newsock);
 	if (retval < 0)
-		goto out;
+		return retval;
 
-	/* Map the socket to an unused fd that can be returned to the user.  */
-	retval = get_unused_fd_flags(flags & SOCK_CLOEXEC);
-	if (retval < 0) {
+	/* Map the socket to a reserved fd that can be returned to the user. */
+	fd = fd_prepare(flags & SOCK_CLOEXEC);
+	if (IS_ERR(fd)) {
 		sock_release(newsock);
-		goto out;
-	}
-
-	*newfile = sock_alloc_file(newsock, 0, NULL);
-	if (IS_ERR(*newfile)) {
-		put_unused_fd(retval);
-		retval = PTR_ERR(*newfile);
-		*newfile = NULL;
-		return retval;
+		return PTR_ERR(fd);
 	}
 
-	pr_debug("%s: sk:%p, newsk:%p, sd:%d\n", __func__, sk, newsock->sk,
-		 retval);
-
-	peeloff->sd = retval;
+	newfile = sock_alloc_file(newsock, 0, NULL);
+	if (IS_ERR(newfile))
+		return PTR_ERR(newfile);
 
 	if (flags & SOCK_NONBLOCK)
-		(*newfile)->f_flags |= O_NONBLOCK;
-out:
-	return retval;
+		newfile->f_flags |= O_NONBLOCK;
+
+	peeloff->sd = fd_stage(fd, newfile);
+	pr_debug("%s: sk:%p, newsk:%p, sd:%d\n", __func__, sk, newsock->sk,
+		 peeloff->sd);
+	return peeloff->sd;
 }
 
 static int sctp_getsockopt_peeloff(struct sock *sk, int len, char __user *optval, int __user *optlen)
 {
 	sctp_peeloff_arg_t peeloff;
-	struct file *newfile = NULL;
-	int retval = 0;
+	int retval;
 
 	if (len < sizeof(sctp_peeloff_arg_t))
 		return -EINVAL;
@@ -5791,24 +5786,17 @@ static int sctp_getsockopt_peeloff(struct sock *sk, int len, char __user *optval
 	if (copy_from_user(&peeloff, optval, len))
 		return -EFAULT;
 
-	retval = sctp_getsockopt_peeloff_common(sk, &peeloff, &newfile, 0);
+	retval = sctp_getsockopt_peeloff_common(sk, &peeloff, 0);
 	if (retval < 0)
-		goto out;
+		return retval;
 
 	/* Return the fd mapped to the new socket.  */
-	if (put_user(len, optlen)) {
-		fput(newfile);
-		put_unused_fd(retval);
+	if (put_user(len, optlen))
 		return -EFAULT;
-	}
 
-	if (copy_to_user(optval, &peeloff, len)) {
-		fput(newfile);
-		put_unused_fd(retval);
+	if (copy_to_user(optval, &peeloff, len))
 		return -EFAULT;
-	}
-	fd_install(retval, newfile);
-out:
+
 	return retval;
 }
 
@@ -5816,8 +5804,7 @@ static int sctp_getsockopt_peeloff_flags(struct sock *sk, int len,
 					 char __user *optval, int __user *optlen)
 {
 	sctp_peeloff_flags_arg_t peeloff;
-	struct file *newfile = NULL;
-	int retval = 0;
+	int retval;
 
 	if (len < sizeof(sctp_peeloff_flags_arg_t))
 		return -EINVAL;
@@ -5826,24 +5813,17 @@ static int sctp_getsockopt_peeloff_flags(struct sock *sk, int len,
 		return -EFAULT;
 
 	retval = sctp_getsockopt_peeloff_common(sk, &peeloff.p_arg,
-						&newfile, peeloff.flags);
+						peeloff.flags);
 	if (retval < 0)
-		goto out;
+		return retval;
 
 	/* Return the fd mapped to the new socket.  */
-	if (put_user(len, optlen)) {
-		fput(newfile);
-		put_unused_fd(retval);
+	if (put_user(len, optlen))
 		return -EFAULT;
-	}
 
-	if (copy_to_user(optval, &peeloff, len)) {
-		fput(newfile);
-		put_unused_fd(retval);
+	if (copy_to_user(optval, &peeloff, len))
 		return -EFAULT;
-	}
-	fd_install(retval, newfile);
-out:
+
 	return retval;
 }
 

-- 
2.53.0