linux-kernel - Re: BUG: Mount ignores mount options

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Message-ID: <79f05de7-e600-675d-7bbf-c56faafc3134@i-love.sakura.ne.jp>
Date:   Sat, 11 Aug 2018 00:11:47 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        David Howells <dhowells@...hat.com>
Cc:     viro@...iv.linux.org.uk,
        John Johansen <john.johansen@...onical.com>,
        Tejun Heo <tj@...nel.org>, selinux@...ho.nsa.gov,
        Paul Moore <paul@...l-moore.com>,
        Li Zefan <lizefan@...wei.com>, linux-api@...r.kernel.org,
        apparmor@...ts.ubuntu.com,
        Casey Schaufler <casey@...aufler-ca.com>, fenghua.yu@...el.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-security-module@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        tomoyo-dev-en@...ts.sourceforge.jp, cgroups@...r.kernel.org,
        torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, "Theodore Y. Ts'o" <tytso@....edu>,
        Miklos Szeredi <miklos@...redi.hu>
Subject: Re: BUG: Mount ignores mount options

On 2018/08/10 23:05, Eric W. Biederman wrote:
> 
> There is a serious problem with mount options today that fsopen does not
> address.  The problem is that mount options are ignored for block based
> filesystems, and any other type of filesystem that follows the same
> pattern.
> 
> The script below demonstrates this bug.  Showing this bug can cause the
> ext4 "acl" "quota" and "user_xattr" options to be silently ignored.
> 
> fsopen has my nack until it addresses this issue.
> 
> I don't know if we can fix this in the context of sys_mount.  But we if
> we are redoing the option parsing of how we mount filesystems this needs
> to be fixed before we start worrying about bug compatibility.
> 
> Hopefully this report is simple and clear enough that we can at least
> agree on the problem.
> 
> Eric

This might be related to a problem that syzbot is failing to reproduce a problem.

  https://groups.google.com/forum/#!msg/syzkaller-bugs/R03vI7RCVco/0PijCTrcCgAJ

  syzbot found a reproducer, and the reproducer was working until next-20180803.
  But the reproducer is failing to reproduce this problem in next-20180806 despite
  there is no mm related change between next-20180803 and next-20180806.

  Therefore, I suspect that the reproducer is no longer working as intended. And
  there was parser change (David Howells' patch) between next-20180803 and next-20180806.

I'm waiting for response from David Howells...