linux-kernel - Re: [PATCH V1] fuse: Abort the requests under processing queue with a spin

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Message-ID: <CAJfpegtr4dZkLzWD_ezAbFgTnbYaGDRq4TR1DUzz4AfFLSLJEA@mail.gmail.com>
Date:   Wed, 31 May 2023 13:52:09 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Pradeep P V K <quic_pragalla@...cinc.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V1] fuse: Abort the requests under processing queue with a spin_lock

On Wed, 31 May 2023 at 11:26, Pradeep P V K <quic_pragalla@...cinc.com> wrote:
>
> There is a potential race/timing issue while aborting the
> requests on processing list between fuse_dev_release() and
> fuse_abort_conn(). This is resulting into below warnings
> and can even result into UAF issues.

Okay, but...

>
> [22809.190255][T31644] refcount_t: underflow; use-after-free.
> [22809.190266][T31644] WARNING: CPU: 2 PID: 31644 at lib/refcount.c:28
> refcount_warn_saturate+0x110/0x158
> ...
> [22809.190567][T31644] Call trace:
> [22809.190567][T31644]  refcount_warn_saturate+0x110/0x158
> [22809.190569][T31644]  fuse_file_put+0xfc/0x104

...how can this cause the file refcount to underflow?  That would
imply that fuse_request_end() will be called for the same request
twice.  I can't see how that can happen with or without the locking
change.

Do you have a reproducer?

Thanks,
Miklos