io_uring: fix UAF due to missing POLLFREE handling

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Fixes a problem described in 50252e4b5e
("aio: fix use-after-free due to missing POLLFREE handling")
and copies the approach used there.

In short, we have to forcibly eject a poll entry when we meet POLLFREE.
We can't rely on io_poll_get_ownership() as can't wait for potentially
running tw handlers, so we use the fact that wqs are RCU freed. See
Eric's patch and comments for more details.

Reported-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20211209010455.42744-6-ebiggers@kernel.org
Reported-and-tested-by: syzbot+5426c7ed6868c705ca14@syzkaller.appspotmail.com
Fixes: 221c5eb233 ("io_uring: add support for IORING_OP_POLL")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/4ed56b6f548f7ea337603a82315750449412748a.1642161259.git.asml.silence@gmail.com
[axboe: drop non-functional change from patch]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

...

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Pavel Begunkov 2022-01-14 11:59:10 +00:00 • committed by Jens Axboe

parent c84b8a3fef

commit 791f3465c4

1 changed files with 50 additions and 8 deletions

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fs/io_uring.c

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