On Mon, Aug 31, 2020 at 02:23:53PM -0400, Qian Cai wrote:
> It is trivial to trigger a WARN_ON_ONCE(1) in iomap_dio_actor() by
> unprivileged users which would taint the kernel, or worse - panic if
> panic_on_warn or panic_on_taint is set. Hence, just convert it to
> pr_warn_ratelimited() to let users know their workloads are racing.
> Thank Dave Chinner for the initial analysis of the racing reproducers.
>
> Signed-off-by: Qian Cai <cai@xxxxxx>
Looks ok to me too.
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> v4: use %pD4.
> v3: Keep the default case and update the message.
> v2: Record the path, pid and command as well.
>
> fs/iomap/direct-io.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index c1aafb2ab990..9519113ebc35 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -388,6 +388,16 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
> return iomap_dio_bio_actor(inode, pos, length, dio, iomap);
> case IOMAP_INLINE:
> return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
> + case IOMAP_DELALLOC:
> + /*
> + * DIO is not serialised against mmap() access at all, and so
> + * if the page_mkwrite occurs between the writeback and the
> + * iomap_apply() call in the DIO path, then it will see the
> + * DELALLOC block that the page-mkwrite allocated.
> + */
> + pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %pD4 Comm: %.20s\n",
> + dio->iocb->ki_filp, current->comm);
> + return -EIO;
> default:
> WARN_ON_ONCE(1);
> return -EIO;
> --
> 2.18.4
>
