On Thu, Oct 15, 2020 at 05:13:35PM +0800, Xiaoguang Wang wrote:
> Reading codes finds a possible use after free issue to sqd:
> thread1 | thread2
> ==> io_attach_sq_data() |
> ===> sqd = ctx_attach->sq_data;|
> | ==> io_put_sq_data()
> | ===> refcount_dec_and_test(&sqd->refs)
> | If sqd->refs is zero, will free sqd.
> |
> ===> refcount_inc(&sqd->refs); |
> |
> | ====> kfree(sqd);
> ===> now use after free to sqd |
>
IIUC the io_attach_sq_data() is called only during the setup of an
io_uring context, before that the fd is returned to the user space.
So, I'm not sure a second thread can call io_put_sq_data() while the
first thread is in io_attach_sq_data().
Can you check if this situation can really happen?
Thanks,
Stefano
> Use refcount_inc_not_zero() to fix this issue.
>
> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
> ---
> fs/io_uring.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 33b5cf18bb51..48e230feb704 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -6868,7 +6868,11 @@ static struct io_sq_data *io_attach_sq_data(struct io_uring_params *p)
> return ERR_PTR(-EINVAL);
> }
>
> - refcount_inc(&sqd->refs);
> + if (!refcount_inc_not_zero(&sqd->refs)) {
> + fdput(f);
> + return ERR_PTR(-EINVAL);
> + }
> +
> fdput(f);
> return sqd;
> }
> --
> 2.17.2
>
