[PATCH] kernel/watch_queue: Make pipe NULL while clearing watch_queue

[Siddh Raman Pant]

On Sun, 31 Jul 2022 23:41:31 +0530  Dipanjan Das <mail.dipanjan.das at gmail.com> wrote:
> On Wed, Jul 27, 2022 at 09:50:52PM +0530, Siddh Raman Pant wrote:
> > Thank you for explaining it!
> > 
> > I will send a v3. Should I add a Suggested-by tag mentioning you?
> 
> Sorry for jumping in.
> 
> We have reported the same bug in kernel v5.10.131 [https://lore.kernel.org/all/CANX2M5bHye2ZEEhEV6PUj1kYL2KdWYeJtgXw8KZRzwrNpLYz+A@mail.gmail.com]. We have been suggested to join this discussion so that we can have appropriate meta-information injected in this patch’s commit message to make sure that it gets backported to v5.10.y.  Therefore, we would like to be in the loop so that we can offer help in the process, if needed.
> 

As you are suggesting for backporting, I should CC the stable list, or mail
after it gets merged. You have reproduced it on v5.10, but the change seems to
be introduced by c73be61cede5 ("pipe: Add general notification queue support"),
which got in at v5.8. So should it be backported till v5.8 instead?

I actually looked this up on the internet / lore now for any other reports, and
it seems this fixes a CVE (CVE-2022-1882).

The reporter of CVE seems to have linked his patch as a part of CVE report, of
which he sent v2, but he seems to do it in a roundabout way, and also in a way
similar to what Hillf Danton had replied to my v2 patch, wherein he missed
353f7988dd84 ("watchqueue: make sure to serialize 'wqueue->defunct' properly"),
so I guess I can propose my patch as a fix for the CVE.

Note: I have already sent the v3, so please suggest any new improvements etc.
(except replying to the conversation here) to the v3, which can be found here:
https://lore.kernel.org/linux-kernel/20220728155121.12145-1-code@siddh.me/

Also, you may want to break text into multiples lines instead of one huge line.

Thanks,
Siddh