[PATCH v2 06/16] remap_range: move permission hooks out of do_clone_file_range()

[Amir Goldstein <amir73il@gmail.com>]

In many of the vfs helpers, file permission hook is called before
taking sb_start_write(), making them "start-write-safe".
do_clone_file_range() is an exception to this rule.

do_clone_file_range() has two callers - vfs_clone_file_range() and
overlayfs. Move remap_verify_area() checks from do_clone_file_range()
out to vfs_clone_file_range() to make them "start-write-safe".

Overlayfs already has calls to rw_verify_area() with the same security
permission hooks as remap_verify_area() has.
The rest of the checks in remap_verify_area() are irrelevant for
overlayfs that calls do_clone_file_range() offset 0 and positive length.

This is needed for fanotify "pre content" events.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/remap_range.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/remap_range.c b/fs/remap_range.c
index 87ae4f0dc3aa..42f79cb2b1b1 100644
--- a/fs/remap_range.c
+++ b/fs/remap_range.c
@@ -385,14 +385,6 @@ loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
 	if (!file_in->f_op->remap_file_range)
 		return -EOPNOTSUPP;
 
-	ret = remap_verify_area(file_in, pos_in, len, false);
-	if (ret)
-		return ret;
-
-	ret = remap_verify_area(file_out, pos_out, len, true);
-	if (ret)
-		return ret;
-
 	ret = file_in->f_op->remap_file_range(file_in, pos_in,
 			file_out, pos_out, len, remap_flags);
 	if (ret < 0)
@@ -410,6 +402,14 @@ loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in,
 {
 	loff_t ret;
 
+	ret = remap_verify_area(file_in, pos_in, len, false);
+	if (ret)
+		return ret;
+
+	ret = remap_verify_area(file_out, pos_out, len, true);
+	if (ret)
+		return ret;
+
 	file_start_write(file_out);
 	ret = do_clone_file_range(file_in, pos_in, file_out, pos_out, len,
 				  remap_flags);
-- 
2.34.1