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From: Josef Bacik <josef@toxicpanda.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org,
	Amir Goldstein <amir73il@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	syzbot+701037856c25b143f1ad@syzkaller.appspotmail.com
Subject: Re: [PATCH v2] fsnotify: Avoid data race between fsnotify_recalc_mask() and fsnotify_object_watched()
Date: Mon, 15 Jul 2024 10:22:03 -0400	[thread overview]
Message-ID: <20240715142203.GA1649877@perftesting> (raw)
In-Reply-To: <20240715130410.30475-1-jack@suse.cz>

On Mon, Jul 15, 2024 at 03:04:10PM +0200, Jan Kara wrote:
> When __fsnotify_recalc_mask() recomputes the mask on the watched object,
> the compiler can "optimize" the code to perform partial updates to the
> mask (including zeroing it at the beginning). Thus places checking
> the object mask without conn->lock such as fsnotify_object_watched()
> could see invalid states of the mask. Make sure the mask update is
> performed by one memory store using WRITE_ONCE().
> 
> Reported-by: syzbot+701037856c25b143f1ad@syzkaller.appspotmail.com
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Link: https://lore.kernel.org/all/CACT4Y+Zk0ohwwwHSD63U2-PQ=UuamXczr1mKBD6xtj2dyYKBvA@mail.gmail.com
> Signed-off-by: Jan Kara <jack@suse.cz>

I'm still hazy on the rules here and what KCSAN expects, but if we're using
READ_ONCE/WRITE_ONCE on a thing, do we have to use them everywhere we access
that member?  Because there's a few accesses in include/linux/fsnotify_backend.h
that were missed if so.  Thanks,

Josef

  reply	other threads:[~2024-07-15 14:22 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-07-15 13:04 [PATCH v2] fsnotify: Avoid data race between fsnotify_recalc_mask() and fsnotify_object_watched() Jan Kara
2024-07-15 14:22 ` Josef Bacik [this message]
2024-07-15 14:48   ` Marco Elver
2024-07-17 13:16   ` Jan Kara

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