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SubjectRe: [PATCH 10/32] aio: implement IOCB_CMD_POLL
On Tue, May 15, 2018 at 09:48:11PM +0200, Christoph Hellwig wrote:
> +static ssize_t aio_poll(struct aio_kiocb *aiocb, struct iocb *iocb)
> +{
> + struct kioctx *ctx = aiocb->ki_ctx;
> + struct poll_iocb *req = &aiocb->poll;
> + unsigned long flags;
> + __poll_t mask;
> +
> + /* reject any unknown events outside the normal event mask. */
> + if ((u16)iocb->aio_buf != iocb->aio_buf)
> + return -EINVAL;
> + /* reject fields that are not defined for poll */
> + if (iocb->aio_offset || iocb->aio_nbytes || iocb->aio_rw_flags)
> + return -EINVAL;
> +
> + req->events = demangle_poll(iocb->aio_buf) | POLLERR | POLLHUP;
> + req->file = fget(iocb->aio_fildes);
> + if (unlikely(!req->file))
> + return -EBADF;
> + if (!file_has_poll_mask(req->file))
> + goto out_fail;
> +
> + req->head = req->file->f_op->get_poll_head(req->file, req->events);
> + if (!req->head)
> + goto out_fail;
> + if (IS_ERR(req->head)) {
> + mask = EPOLLERR;
> + goto done;
> + }
> +
> + init_waitqueue_func_entry(&req->wait, aio_poll_wake);
> + aiocb->ki_cancel = aio_poll_cancel;
> +
> + spin_lock_irqsave(&ctx->ctx_lock, flags);
> + list_add_tail(&aiocb->ki_list, &ctx->delayed_cancel_reqs);
> + spin_unlock(&ctx->ctx_lock);

... and io_cancel(2) comes, finds it and inhume^Wcompletes it, leaving us to...

> + spin_lock(&req->head->lock);

... get buggered on attempt to dereference a pointer fetched from freed and
reused object.

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