linux-kernel - Re: [PATCH vfs/for-next 00/18] fs

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Date:   Sun, 8 Jul 2018 16:46:30 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     David Howells <dhowells@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH vfs/for-next 00/18] fs_context fixes

On Sun, Jul 08, 2018 at 02:01:36PM -0700, Eric Biggers wrote:
> Hi David and Al, here are some fixes for the fs_context patches.
> 
> Feel free to fold these into the original patches if you want.
> 
> Patches 13-18 are cleanups only.
> 

Also, mount(..., MS_REMOUNT|MS_BIND, ...) now validates the mount options
string, which breaks systemd unit files with ProtectControlGroups=yes (e.g.
systemd-networkd.service) when systemd does the following to change a cgroup
(v1) mount to read-only:

    mount(NULL, "/run/systemd/unit-root/sys/fs/cgroup/systemd", NULL, MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_REMOUNT|MS_BIND, NULL)

... when the kernel has CONFIG_CGROUPS=y but no cgroup subsystems enabled, since
in that case the error "cgroup1: Need name or subsystem set" is hit when the
mount options string is empty.

Probably it doesn't make sense to validate the mount options string at all in
the MS_REMOUNT|MS_BIND case, though maybe you had something else in mind.

- Eric