linux-kernel - [PATCH] vfs: allow FILE_EXTENT_SAME (dedupe_file

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Message-Id: <1468793618-10496-1-git-send-email-kilobyte@angband.pl>
Date:	Mon, 18 Jul 2016 00:13:38 +0200
From:	Adam Borowski <kilobyte@...band.pl>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, Mark Fasheh <mfasheh@...e.de>,
	"Darrick J . Wong" <darrick.wong@...cle.com>
Cc:	Adam Borowski <kilobyte@...band.pl>
Subject: [PATCH] vfs: allow FILE_EXTENT_SAME (dedupe_file_range) on a file opened ro

Instead of checking the mode of the file descriptor, let's check whether it
could have been opened rw.  This allows fixing intermittent exec failures
when deduping a live system: anyone trying to exec a file currently being
deduped gets ETXTBSY.

Issuing this ioctl on a ro file was already allowed for root/cap.

Tested on btrfs and not-yet-merged xfs, as only them implement this ioctl.

Signed-off-by: Adam Borowski <kilobyte@...band.pl>
---
 fs/read_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 933b53a..df59dc6 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1723,7 +1723,7 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
 
 		if (info->reserved) {
 			info->status = -EINVAL;
-		} else if (!(is_admin || (dst_file->f_mode & FMODE_WRITE))) {
+		} else if (!(is_admin || !inode_permission(dst, MAY_WRITE))) {
 			info->status = -EINVAL;
 		} else if (file->f_path.mnt != dst_file->f_path.mnt) {
 			info->status = -EXDEV;
-- 
2.8.1