Re: [PATCH] autofs: fix wait name hash calculation in autofs_wait()

[Ian Kent <raven@themaw.net>]

On Thu, 2021-10-14 at 10:11 -0500, Justin Forbes wrote:
> 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.

Yes, but what the patch description is talking about is my not
discovering the problem when I tested the original change.

I have a similar Fedora bug too but that came in some time after
I discovered the problem when testing a new autofs release.

All it takes is multiple processes concurrently triggering an
autofs automount point. Because the qstr hash doesn't match
duplicate mount requests are sent to the daemon which is a
problem.

> 
> 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);
> > 
> >