Re: 5.10.225 stable kernel cgroup_mutex not held assertion failure

Shivani Agarwal
2024-09-20T09:28:11Z

> we've also encountered this problem. The thing is that commit 688325078a8b
> ("cgroup/cpuset: Prevent UAF in proc_cpuset_show()") relies on the RCU
> synchronization changes introduced by commit d23b5c577715 ("cgroup: Make
> operations on the cgroup root_list RCU safe") which wasn't backported to
> 5.10 as it couldn't be cleanly applied there. That commit converted access
> to the root_list synchronization from depending on cgroup mutex to be
> RCU-safe.

> 5.15 also has this problem, while 6.1 and later stables have the backport
> of this RCU-changing commit so they are not affected. As mentioned by
> Michal here:
> https://lore.kernel.org/stable/xrc6s5oyf3b5hflsffklogluuvd75h2khanrke2laes3en5js2@6kvpkcxs7ufj/

> In the next email I'll send the adapted to 5.10/5.15 commit along with its
> upstream-fix to avoid build failure in some situations. Would be nice if
> you give them a try. Thanks!

Thanks Fedor.

Upstream commit 1be59c97c83c is merged in 5.4 with commit 10aeaa47e4aa and
in 4.19 with commit 27d6dbdc6485. The issue is reproducible in 5.4 and 4.19
also.

I am sending the backport patch of d23b5c577715 and a7fb0423c201 for 5.4 and
4.19 in the next email.

Thanks,
Shivani