linux-kernel - Re: [PATCH v5] aio: Add support for the POLLFREE

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Date:   Tue, 23 Nov 2021 11:49:54 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Benjamin LaHaise <bcrl@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Ramji Jiyani <ramjiyani@...gle.com>, arnd@...db.de, hch@....de,
        kernel-team@...roid.com, linux-aio@...ck.org,
        linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, oleg@...hat.com,
        Jeff Moyer <jmoyer@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH v5] aio: Add support for the POLLFREE

On Wed, Oct 27, 2021 at 01:18:34AM +0000, Ramji Jiyani wrote:
> Add support for the POLLFREE flag to force complete iocb inline in
> aio_poll_wake(). A thread may use it to signal it's exit and/or request
> to cleanup while pending poll request. In this case, aio_poll_wake()
> needs to make sure it doesn't keep any reference to the queue entry
> before returning from wake to avoid possible use after free via
> poll_cancel() path.
> 
> UAF issue was found during binder and aio interactions in certain
> sequence of events [1].
> 
> The POLLFREE flag is no more exclusive to the epoll and is being
> shared with the aio. Remove comment from poll.h to avoid confusion.
> 
> [1] https://lore.kernel.org/r/CAKUd0B_TCXRY4h1hTztfwWbNSFQqsudDLn2S_28csgWZmZAG3Q@mail.gmail.com/
> 
> Fixes: af5c72b1fc7a ("Fix aio_poll() races")
> Signed-off-by: Ramji Jiyani <ramjiyani@...gle.com>
> Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Cc: stable@...r.kernel.org # 4.19+
> ---

Looks good, feel free to add:

	Reviewed-by: Eric Biggers <ebiggers@...gle.com>

I'm still not 100% happy with the commit message, but it's good enough.
The actual code looks correct.

Who is going to take this patch?  This is an important fix; it shouldn't be
sitting ignored for months.  get_maintainer.pl shows:

$ ./scripts/get_maintainer.pl fs/aio.c
Benjamin LaHaise <bcrl@...ck.org> (supporter:AIO)
Alexander Viro <viro@...iv.linux.org.uk> (maintainer:FILESYSTEMS (VFS and infrastructure))
linux-aio@...ck.org (open list:AIO)
linux-fsdevel@...r.kernel.org (open list:FILESYSTEMS (VFS and infrastructure))
linux-kernel@...r.kernel.org (open list)

- Eric