On Mon, Mar 04, 2024 at 10:29:44AM -0800, Bart Van Assche wrote:
> Patch "fs/aio: Make io_cancel() generate completions again" is based on the
> assumption that calling kiocb->ki_cancel() does not complete R/W requests.
> This is incorrect: the two drivers that call kiocb_set_cancel_fn() callers
> set a cancellation function that calls usb_ep_dequeue(). According to its
> documentation, usb_ep_dequeue() calls the completion routine with status
> -ECONNRESET. Hence this revert.
>
> Cc: Benjamin LaHaise <ben@xxxxxxxxxxxxxxxxx>
> Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Avi Kivity <avi@xxxxxxxxxxxx>
> Cc: Sandeep Dhavale <dhavale@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: syzbot+b91eb2ed18f599dd3c31@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 54cbc058d86b ("fs/aio: Make io_cancel() generate completions again")
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> fs/aio.c | 27 ++++++++++++++++-----------
> 1 file changed, 16 insertions(+), 11 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 28223f511931..da18dbcfcb22 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -2165,11 +2165,14 @@ COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
> #endif
>
> /* sys_io_cancel:
> - * Attempts to cancel an iocb previously passed to io_submit(). If the
> - * operation is successfully cancelled 0 is returned. May fail with
> - * -EFAULT if any of the data structures pointed to are invalid. May
> - * fail with -EINVAL if aio_context specified by ctx_id is invalid. Will
> - * fail with -ENOSYS if not implemented.
> + * Attempts to cancel an iocb previously passed to io_submit. If
> + * the operation is successfully cancelled, the resulting event is
> + * copied into the memory pointed to by result without being placed
> + * into the completion queue and 0 is returned. May fail with
> + * -EFAULT if any of the data structures pointed to are invalid.
> + * May fail with -EINVAL if aio_context specified by ctx_id is
> + * invalid. May fail with -EAGAIN if the iocb specified was not
> + * cancelled. Will fail with -ENOSYS if not implemented.
> */
> SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
> struct io_event __user *, result)
> @@ -2200,12 +2203,14 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
> }
> spin_unlock_irq(&ctx->ctx_lock);
>
> - /*
> - * The result argument is no longer used - the io_event is always
> - * delivered via the ring buffer.
> - */
> - if (ret == 0 && kiocb->rw.ki_flags & IOCB_AIO_RW)
> - aio_complete_rw(&kiocb->rw, -EINTR);
> + if (!ret) {
> + /*
> + * The result argument is no longer used - the io_event is
> + * always delivered via the ring buffer. -EINPROGRESS indicates
> + * cancellation is progress:
> + */
> + ret = -EINPROGRESS;
> + }
Acked-by: Eric Biggers <ebiggers@xxxxxxxxxx>
It does look like all the ->ki_cancel functions complete the request already, so
this patch was unnecessary and just introduced a bug.
Note that IOCB_CMD_POLL installs a ->ki_cancel function too, and that's how
syzbot hit the use-after-free so easily.
I assume that the patch just wasn't tested? Or did you find that it actually
fixed something (how)?
By the way, libaio (https://pagure.io/libaio) has a test suite for these system
calls. How about adding a test case that cancels an IOCB_CMD_POLL request and
verifies that the completion event is received?
- Eric
