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/ (local)

Fixes: af5c72b1fc7a ("Fix aio_poll() races")
Signed-off-by: Ramji Jiyani <redacted>
Reviewed-by: Jeff Moyer <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org # 4.19+
---

Looks good, feel free to add:

	Reviewed-by: Eric Biggers [off-list ref]

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 [off-list ref] (supporter:AIO)
Alexander Viro [off-list ref] (maintainer:FILESYSTEMS (VFS and infrastructure))
linux-aio@kvack.org (open list:AIO)
linux-fsdevel@vger.kernel.org (open list:FILESYSTEMS (VFS and infrastructure))
linux-kernel@vger.kernel.org (open list)

- Eric