Re: [PATCH 1/6] blk-mq: Do not invoke queue operations on a dead queue

Omar Sandoval
2017-04-13T23:01:02Z

On Tue, Apr 11, 2017 at 01:58:37PM -0700, Bart Van Assche wrote:
> The blk-mq debugfs attributes are removed after blk_cleanup_queue()
> has finished. Since running a queue after a queue has entered the
> "dead" state is not allowed, disallow this. This patch avoids that
> an attempt to run a dead queue triggers a kernel crash.
>
> Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
> Cc: Omar Sandoval <osandov@fb.com>
> Cc: Hannes Reinecke <hare@suse.com>
> ---
> block/blk-mq-debugfs.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
> index df9b688b877c..a1ce823578c7 100644
> --- a/block/blk-mq-debugfs.c
> +++ b/block/blk-mq-debugfs.c
> @@ -111,6 +111,14 @@ static ssize_t blk_queue_flags_store(struct file *file, const char __user *ubuf,
> struct request_queue *q = file_inode(file)->i_private;
> char op[16] = { }, *s;
>
> + /*
> + * The debugfs attributes are removed after blk_cleanup_queue() has
> + * called blk_mq_free_queue(). Return if QUEUE_FLAG_DEAD has been set
> + * to avoid triggering a use-after-free.
> + */
> + if (blk_queue_dead(q))
> + return -ENOENT;
> +
> len = min(len, sizeof(op) - 1);
> if (copy_from_user(op, ubuf, len))
> return -EFAULT;
> --
> 2.12.0
>

Hi, Bart,

Looking at this, I think we have similar issues with most of the other
debugfs files. Should we move the debugfs cleanup earlier?