linux-kernel - Re: [PATCH v3] kernel/watch_queue: Make pipe NULL while clearing watch

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Date:   Thu, 04 Aug 2022 14:09:36 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     "Eric Biggers" <ebiggers@...nel.org>
Cc:     "David Howells" <dhowells@...hat.com>,
        "Christophe JAILLET" <christophe.jaillet@...adoo.fr>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        "linux-security-modules" <linux-security-module@...r.kernel.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "linux-kernel-mentees" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        "syzbot+c70d87ac1d001f29a058" 
        <syzbot+c70d87ac1d001f29a058@...kaller.appspotmail.com>
Subject: Re: [PATCH v3] kernel/watch_queue: Make pipe NULL while clearing
 watch_queue

On Wed, 03 Aug 2022 23:45:31 +0530  Eric Biggers  wrote:
> Well, you should try listening instead.  Because you are not listening.

Sorry for that, never meant to come across like that.

> Even if wqueue->pipe was set to NULL during free_pipe_info(), there would still
> have been a use-after-free, as the real bug was the lack of synchronization
> between post_one_notification() and free_pipe_info().  That is fixed now.

Okay, noted.

> To re-iterate, I encourage you to send a cleanup patch if you see an
> opportunity.  It looks like the state wqueue->defunct==true could be replaced
> with wqueue->pipe==NULL, which would be simpler, so how about doing that?  Just
> don't claim that it is "fixing" something, unless it is, as that makes things
> very confusing and difficult for everyone.

Okay, I will do that. That actually seems like a plausible thing to do, in
v2 convo, David Howells had also remarked similarly about `defunct` to a reply.

https://lore.kernel.org/linux-kernel/3565221.1658933355@warthog.procyon.org.uk/

> A reproducer can just be written as a normal program, in C or another language.
> The syzkaller reproducers are really hard to read as they are auto-generated, so
> don't read too much into them -- they're certainly not examples of good code.
> 
> - Eric

Okay, noted.

Thanks for your patience, I probably annoyed you.

Thanks,
Siddh