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From:   Justin Forbes <jmforbes@linuxtx.org>
Date:   Thu, 14 Oct 2021 10:11:22 -0500
Message-ID: <CAFxkdAraAe37_5bGLJtTtxZCaKTqgVPh4hTbcVC=08vRt-Zizg@mail.gmail.com>
Subject: Re: [PATCH] autofs: fix wait name hash calculation in autofs_wait()
To:     Ian Kent <raven@themaw.net>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        autofs mailing list <autofs@vger.kernel.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
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On Thu, Sep 23, 2021 at 2:20 AM Ian Kent <raven@themaw.net> wrote:
>
> There's a mistake in commit 2be7828c9fefc ("get rid of autofs_getpath()")
> that affects kernels from v5.13.0, basically missed because of me not
> fully testing the change for Al.
>
> The problem is that the hash calculation for the wait name qstr hasn't
> been updated to account for the change to use dentry_path_raw(). This
> prevents the correct matching an existing wait resulting in multiple
> notifications being sent to the daemon for the same mount which must
> not occur.
>
> The problem wasn't discovered earlier because it only occurs when
> multiple processes trigger a request for the same mount concurrently
> so it only shows up in more aggressive testing.

I suppose it shows up in more than just testing, as we have a bug
where this is impacting a user doing regular desktop things.

Justin

> Fixes: 2be7828c9fefc ("get rid of autofs_getpath()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ian Kent <raven@themaw.net>
> ---
>  fs/autofs/waitq.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/autofs/waitq.c b/fs/autofs/waitq.c
> index 16b5fca0626e..54c1f8b8b075 100644
> --- a/fs/autofs/waitq.c
> +++ b/fs/autofs/waitq.c
> @@ -358,7 +358,7 @@ int autofs_wait(struct autofs_sb_info *sbi,
>                 qstr.len = strlen(p);
>                 offset = p - name;
>         }
> -       qstr.hash = full_name_hash(dentry, name, qstr.len);
> +       qstr.hash = full_name_hash(dentry, qstr.name, qstr.len);
>
>         if (mutex_lock_interruptible(&sbi->wq_mutex)) {
>                 kfree(name);
>
>