[resend] vfs: allow FILE_EXTENT_SAME (dedupe_file_range) on a file opened ro
diff mbox

Message ID 20161005143854.17133-1-kilobyte@angband.pl
State New
Headers show

Commit Message

Adam Borowski Oct. 5, 2016, 2:38 p.m. UTC
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@angband.pl>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>
---
 fs/read_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Adam Borowski Oct. 12, 2016, 10:15 p.m. UTC | #1
On Wed, Oct 05, 2016 at 04:38:54PM +0200, Adam Borowski wrote:
> [fix for dedupe-vs-exec ETXTBSY]
> Reviewed-by: Mark Fasheh <mfasheh@suse.de>

Hi guys!
May I ask if I'm doing something wrong, or barking up the wrong tree?  I've
sent this patch thrice (May 20, Jul 18, Oct 5), pinged once (Aug 6), yet it
hasn't been taken nor NACKed yet.  For fixes to vfs core I need to bother Al
Viro, -fsdevel@vger, -kernel@vger, right?

It's not a vital fix (strictly speaking, it only allows to fix userspace),
as save for unprivileged containers, when deduping executables you usually
need to be root anyway -- but it'd still be nice to have it.  It has been
ACKed by the original author of that code.

(Sorry for being annoying, I got only 13 commits elsewhere in the kernel so
please point me in the right direction when hitting :p)

Meow!

Patch
diff mbox

diff --git a/fs/read_write.c b/fs/read_write.c
index 66215a7..8ea5297 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1741,7 +1741,7 @@  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;