Bug 15739

Summary:	readonly attribute of a bind mount is not preserved across bind mounts.
Product:	File System	Reporter:	Tefnet developers (developers)
Component:	VFS	Assignee:	Marshel Abraham (marshel.abraham)
Status:	CLOSED PATCH_ALREADY_AVAILABLE
Severity:	normal	CC:	marshel.abraham
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	2.6.31	Subsystem:
Regression:	No	Bisected commit-id:

Description Tefnet developers 2010-04-09 14:38:21 UTC

root@tefnet:/tmp/bindtest# mkdir -p 1/11 2 3

When I mount -o bind,ro a directory:

root@tefnet:/tmp/bindtest# mount 1 2 -o bind,ro
root@tefnet:/tmp/bindtest# touch 2/foo
touch: cannot touch `2/foo': Read-only file system

and then mount part of it with -o bind:

root@tefnet:/tmp/bindtest# mount 2/11 3 -o bind
root@tefnet:/tmp/bindtest# touch 3/foo
root@tefnet:/tmp/bindtest#

the mounted part is read-write despite no specification of ro/rw option on the mount command line.

I expected the "3" directory to be read-only as well.

Comment 1 Marshel Abraham 2013-05-12 09:06:16 UTC

This issue seems to be solved in the latest kernel. Remember 2.6 onwards kernel doesnt support to bind mount a rw file system to ro, the first step itself doesnt work in my kernel.

root@host:/# mount 1 2 -o bind,ro
mount: warning: 2 seems to be mounted read-write.

http://lwn.net/Articles/281157/

Besides that the filesystem subdirectories tend to retain their properties...

In your case /2 is ro, But /2/11 is rw having inherited from 1/11

So 2/11 which is rw when bind mounted to /3 retains the rw...


Can this issue be closed...?

Comment 2 Tefnet developers 2013-05-12 18:56:21 UTC

Thanks for the update, it seems more reasonable now:

root@klocek:/tmp/bindtest# mkdir -p 1/11 2 3
root@klocek:/tmp/bindtest# mount 1 2 -o bind,ro
mount: warning: 2 seems to be mounted read-write.
root@klocek:/tmp/bindtest# mount 2 -o remount,ro
root@klocek:/tmp/bindtest# touch 2/foo
touch: cannot touch `2/foo': Read-only file system
root@klocek:/tmp/bindtest# mount 2/11 3 -o bind,rw
mount: warning: 3 seems to be mounted read-only.
root@klocek:/tmp/bindtest# touch 3/foo
touch: cannot touch `3/foo': Read-only file system
root@klocek:/tmp/bindtest# 

The original problem I had with that (unexpected write possibilities) does not seem to occur anymore, so I think that the issue can be closed :).

Comment 3 Marshel Abraham 2013-05-14 05:19:51 UTC

Can somebody close this..?