linux-kernel - Re: [PATCH 1/3] autofs - fix AT_NO

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Date:   Tue, 08 Aug 2017 09:11:14 -0400
From:   Colin Walters <walters@...bum.org>
To:     Ian Kent <raven@...maw.net>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     autofs mailing list <autofs@...r.kernel.org>,
        Ondrej Holy <oholy@...hat.com>,
        Colin Walters <walters@...hat.com>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        "linux-fsdevel" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 1/3] autofs - fix AT_NO_AUTOMOUNT not being honored

On Tue, Aug 8, 2017, at 12:26 AM, Ian Kent wrote:

> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3022,8 +3022,7 @@ static inline int vfs_lstat(const char __user *name, struct kstat *stat)
>  static inline int vfs_fstatat(int dfd, const char __user *filename,
>  			      struct kstat *stat, int flags)
>  {
> -	return vfs_statx(dfd, filename, flags | AT_NO_AUTOMOUNT,
> -			 stat, STATX_BASIC_STATS);
> +	return vfs_statx(dfd, filename, flags, stat, STATX_BASIC_STATS);
>  }
>  static inline int vfs_fstat(int fd, struct kstat *stat)
>  {

This is reverting the fstatat() prat of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=deccf497d804a4c5fca2dbfad2f104675a6f9102
Which itself seems weird to me - it looks like we were unconditionally
forcing on AT_NO_AUTOMOUNT regardless of what userspace passed?
So perhaps a
Fixes: deccf497d804a4c5fca2dbfad2f104675a6f9102
is appropriate here?

I understand that for stat()/lstat() we didn't expose the option to userspace,
so the behavior was...ah, there's this note in man-pages (man-pages-4.09-3.fc26.noarch):

> On Linux, lstat() will generally not trigger automounter action, whereas stat() will (but see fstatat(2)).

I have no idea of the history here, but maybe it makes sense to drop
the AT_NO_AUTOMOUNT from the vfs_stat() too?