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

From: Amir Goldstein <amir73il@gmail.com>
To: Christian Brauner <brauner@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>,
	Jens Axboe <axboe@kernel.dk>, Miklos Szeredi <miklos@szeredi.hu>,
	David Howells <dhowells@redhat.com>,
	linux-fsdevel@vger.kernel.org, Chris Mason <clm@fb.com>,
	Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>
Subject: [PATCH 08/15] btrfs: move file_start_write() to after permission hook
Date: Tue, 14 Nov 2023 17:33:14 +0200	[thread overview]
Message-ID: <20231114153321.1716028-9-amir73il@gmail.com> (raw)
In-Reply-To: <20231114153321.1716028-1-amir73il@gmail.com>

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

