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From: Ross Zwisler <zwisler@chromium.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Mattias Nissler <mnissler@chromium.org>,
	Aleksa Sarai <cyphar@cyphar.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Benjamin Gordon <bmgordon@google.com>,
	David Howells <dhowells@redhat.com>,
	Dmitry Torokhov <dtor@google.com>,
	Jesse Barnes <jsbarnes@google.com>,
	linux-fsdevel@vger.kernel.org, Micah Morton <mortonm@google.com>,
	Raul Rangel <rrangel@google.com>
Subject: Re: [PATCH v7] Add a "nosymfollow" mount option.
Date: Wed, 12 Aug 2020 13:53:12 -0600	[thread overview]
Message-ID: <CAGRrVHwCYRXixfft1FCnwU-1UzuoUF3iVayRjD8G_QXX2+nOcQ@mail.gmail.com> (raw)
In-Reply-To: <20200812183557.GB17456@casper.infradead.org>

On Wed, Aug 12, 2020 at 12:36 PM Matthew Wilcox <willy@infradead.org> wrote:
> On Tue, Aug 11, 2020 at 04:28:03PM -0600, Ross Zwisler wrote:
> > diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
> > index 96a0240f23fed..dd8306ea336c1 100644
> > --- a/include/uapi/linux/mount.h
> > +++ b/include/uapi/linux/mount.h
> > @@ -16,6 +16,7 @@
> >  #define MS_REMOUNT   32      /* Alter flags of a mounted FS */
> >  #define MS_MANDLOCK  64      /* Allow mandatory locks on an FS */
> >  #define MS_DIRSYNC   128     /* Directory modifications are synchronous */
> > +#define MS_NOSYMFOLLOW       256     /* Do not follow symlinks */
> >  #define MS_NOATIME   1024    /* Do not update access times. */
> >  #define MS_NODIRATIME        2048    /* Do not update directory access times */
> >  #define MS_BIND              4096
>
> Does this need to be added to MS_RMT_MASK too?

I don't think so, because IIUC that is only for "superblock flags",
i.e. flags which are part of the sb_flags definition in
do_mount()/path_mount()?

https://github.com/torvalds/linux/blob/master/fs/namespace.c#L3172

With the current code I'm able to remount and flip nosymfollow both
directions without issue.  Similarly, MS_NOEXEC can be turned on and
off at will, and it's not part of MS_RMT_MASK nor sb_flags.

Interestingly, though, if you change MS_RMT_MASK to be 0, I would
expect us to be unable to twiddle all the flags which are currently
part of it, but that isn't the case.   I was still able to change
between RO/RW, and turn on lazytime.

So, I think this flag is working as expected, but that there is
probably a bug in there somewhere WRT the handling of MS_RMT_MASK.

      reply	other threads:[~2020-08-12 19:53 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-11 22:28 Ross Zwisler
2020-08-12  1:43 ` Aleksa Sarai
2020-08-12 17:59   ` Ross Zwisler
2020-08-12 18:35 ` Matthew Wilcox
2020-08-12 19:53   ` Ross Zwisler [this message]

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