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A bug in the do_filp_open() function caused it to exit early if any write access was requested on a read-only file system. This prevented the opening of device nodes on a read-only file system. With this update, the do_filp_open() has been fixed to no longer exit if a write request is made on a read-only file system.
Created attachment 709070[details]
patch
Description of problem:
If a filesystem is mounted read-only it is not possible to open device nodes residing on it for writing.
Version-Release number of selected component (if applicable):
kernel-2.6.32-327.el6 and up, introduced in:
1d3c71fcd66a1204fb43f3f06221732c6df1c7c2
Author: Eric Sandeen <sandeen>
Date: Mon Sep 24 21:27:50 2012 -0400
[fs] Push mnt_want_write() outside of i_mutex
How reproducible:
Always
Steps to Reproduce:
1. prepare fs
dd if=/dev/zero of=foo bs=1M count=10
losetup -vf foo
mkfs.ext3 /dev/loop0
mount /dev/loop0 /mnt
mknod /mnt/null c 1 3
umount /mnt
2. mount fs ro: mount -o ro /dev/loop0 /mnt
3. Try to write: echo foo >> /mnt/null
Actual results:
zsh: read-only file system: /mnt/null
Expected results:
successful open + write
This behaviour makes some sense for a read-only file system. Are you looking to make a read-only root for security reasons? Is this a real issue in production or just a feature request?
Thanks!
Ric, we do need to be able to open devices RW even if the device node is on an RO fs. Looks like a regression from the big freeze patchset. I'll take it.
Thanks,
-Eric
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
http://rhn.redhat.com/errata/RHSA-2013-1645.html
Created attachment 709070 [details] patch Description of problem: If a filesystem is mounted read-only it is not possible to open device nodes residing on it for writing. Version-Release number of selected component (if applicable): kernel-2.6.32-327.el6 and up, introduced in: 1d3c71fcd66a1204fb43f3f06221732c6df1c7c2 Author: Eric Sandeen <sandeen> Date: Mon Sep 24 21:27:50 2012 -0400 [fs] Push mnt_want_write() outside of i_mutex How reproducible: Always Steps to Reproduce: 1. prepare fs dd if=/dev/zero of=foo bs=1M count=10 losetup -vf foo mkfs.ext3 /dev/loop0 mount /dev/loop0 /mnt mknod /mnt/null c 1 3 umount /mnt 2. mount fs ro: mount -o ro /dev/loop0 /mnt 3. Try to write: echo foo >> /mnt/null Actual results: zsh: read-only file system: /mnt/null Expected results: successful open + write