On Wed, Oct 6, 2021 at 2:16 PM Eric Biggers [off-list ref] wrote:

On Wed, Oct 06, 2021 at 07:50:29PM +0000, Ramji Jiyani wrote:

quoted

Commit f5cb779ba163 ("ANDROID: binder: remove waitqueue when thread
exits.") fixed the use-after-free in eventpoll but aio still has the
same issue because it doesn't honor the POLLFREE flag.

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.

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.

This fixes a use after free issue between binder thread and aio
interactions in certain sequence of events [1].

[1] https://lore.kernel.org/all/CAKUd0B_TCXRY4h1hTztfwWbNSFQqsudDLn2S_28csgWZmZAG3Q@mail.gmail.com/ (local)

Signed-off-by: Ramji Jiyani <redacted>
Reviewed-by: Jeff Moyer <redacted>

Can you add Fixes and Cc stable tags to ensure that this fix gets backported?
Please refer to Documentation/process/submitting-patches.rst.

- Eric

Thanks Eric. I'll send v3 with these changes soon.

~ Ramji