Re: [PATCH 0/8] blk-mq: fix request UAF related with iterating over tagset requests

[Ming Lei <ming.lei@redhat.com>]

On Sun, Apr 25, 2021 at 01:53:16PM -0700, Bart Van Assche wrote:
> On 4/25/21 2:27 AM, Ming Lei wrote:
> > On Sun, Apr 25, 2021 at 04:57:45PM +0800, Ming Lei wrote:
> >> Revert 4 patches from Bart which try to fix request UAF issue related
> >> with iterating over tagset wide requests, because:
> 
> Where were you during the four weeks that my patch series was out for
> review? I haven't seen any feedback from you on my patch series.

To be honest, it is just two days ago I have to take a close look
at your patchset because we may have to backport your patches for
addressing one RH report with high priority.

David is in CC list, and Laurence/David is looking the report too.

> 
> >> 1) request UAF caused by normal completion vs. async completion during
> >> iterating can't be covered[1]
> 
> I do not agree with the above. Patches 5/8 and 6/8 from this series can
> be applied without reverting any of my patches.

The thing is that 5 ~ 8 can fix the issue in a simpler way without
adding extra cost in fast path, and the idea is easier to be proved.

BTW, as a downstream kernel developer, I really hope all fix are simple and
easy to backport. More importantly, I do prefer to approaches in patch which
can be proved/verified easily, so further regression can be avoided.

> 
> > 4) synchronize_rcu() is added before shutting down one request queue,
> > which may slow down reboot/poweroff very much on big systems with lots of
> > HBAs in which lots of LUNs are attached.
> 
> The synchronize_rcu() can be removed by using a semaphore
> (<linux/semaphore.h>) instead of an RCU reader lock inside bt_tags_iter().

I am not sure you can, because some iteration is done in atomic context.


Thanks,
Ming