[PATCH RFC POC 47/50] iio: buffer: install the buffer descriptor when the ioctl returns

[Christian Brauner]

Rely on the fd exit path machinery.

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 drivers/iio/industrialio-buffer.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index 2c9ec93dff47..9fb15bf82d0a 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -2041,7 +2041,7 @@ static long iio_device_buffer_getfd(struct iio_dev *indio_dev, unsigned long arg
 	int __user *ival = (int __user *)arg;
 	struct iio_dev_buffer_pair *ib;
 	struct iio_buffer *buffer;
-	int fd, idx, ret;
+	int idx, ret, fdno;
 
 	if (copy_from_user(&idx, ival, sizeof(idx)))
 		return -EFAULT;
@@ -2067,26 +2067,18 @@ static long iio_device_buffer_getfd(struct iio_dev *indio_dev, unsigned long arg
 	ib->indio_dev = indio_dev;
 	ib->buffer = buffer;
 
-	fd = anon_inode_getfd("iio:buffer", &iio_buffer_chrdev_fileops,
-			      ib, O_RDWR | O_CLOEXEC);
-	if (fd < 0) {
-		ret = fd;
+	FD_PREPARE(fdf, O_RDWR | O_CLOEXEC,
+		   anon_inode_getfile("iio:buffer", &iio_buffer_chrdev_fileops,
+				      ib, O_RDWR | O_CLOEXEC));
+	if (IS_ERR(fdf)) {
+		ret = PTR_ERR(fdf);
 		goto error_free_ib;
 	}
 
-	if (copy_to_user(ival, &fd, sizeof(fd))) {
-		/*
-		 * "Leak" the fd, as there's not much we can do about this
-		 * anyway. 'fd' might have been closed already, as
-		 * anon_inode_getfd() called fd_install() on it, which made
-		 * it reachable by userland.
-		 *
-		 * Instead of allowing a malicious user to play tricks with
-		 * us, rely on the process exit path to do any necessary
-		 * cleanup, as in releasing the file, if still needed.
-		 */
+	fdno = fd_prepare_fd(fdf);
+	/* The staged file is dropped with its descriptor if this faults. */
+	if (copy_to_user(ival, &fdno, sizeof(fdno)))
 		return -EFAULT;
-	}
 
 	return 0;
 

-- 
2.53.0