[PATCH 08/15] btrfs: move file_start_write() to after permission hook

Amir Goldstein
2023-11-14T15:33:15Z

In vfs code, file_start_write() is usually called after the permission
hook in rw_verify_area(). btrfs_ioctl_encoded_write() in an exception
to this rule.

Move file_start_write() to after the rw_verify_area() check in encoded
write to make the permission hook "start-write-safe".

This is needed for fanotify "pre content" events.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
fs/btrfs/ioctl.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 752acff2c734..e691770c25aa 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4523,29 +4523,29 @@ static int btrfs_ioctl_encoded_write(struct file *file, void __user *argp, bool
if (ret < 0)
goto out_acct;

- file_start_write(file);
-
if (iov_iter_count(&iter) == 0) {
ret = 0;
- goto out_end_write;
+ goto out_iov;
}
pos = args.offset;
ret = rw_verify_area(WRITE, file, &pos, args.len);
if (ret < 0)
- goto out_end_write;
+ goto out_iov;

init_sync_kiocb(&kiocb, file);
ret = kiocb_set_rw_flags(&kiocb, 0);
if (ret)
- goto out_end_write;
+ goto out_iov;
kiocb.ki_pos = pos;

+ file_start_write(file);
+
ret = btrfs_do_write_iter(&kiocb, &iter, &args);
if (ret > 0)
fsnotify_modify(file);

-out_end_write:
file_end_write(file);
+out_iov:
kfree(iov);
out_acct:
if (ret > 0)
--
2.34.1