Re: [PATCH] exit: Retain nsproxy for exit_task_work() work entries

[Michal Koutný]

On Wed, Dec 08, 2021 at 01:07:54PM -1000, Tejun Heo <tj@xxxxxxxxxx> wrote:

> +	saved_cred = override_creds(of->file->f_cred);
>  	ret = cgroup_attach_permissions(src_cgrp, dst_cgrp,
> -					of->file->f_path.dentry->d_sb, threadgroup);
> +					of->file->f_path.dentry->d_sb,
> +					threadgroup, ctx->ns);
> +	revert_creds(saved_cred);

I wonder now whether such a wrap shouldn't also be around cgroup_kill()
too (+ replacement of send_sig() with group_send_sig_info() [1])?

This shouldn't break the use case of passing cgroup kill fd to a less
privileged task for (auto)destruction purposes but on the other hand it
would prevent subverting the fd to a more privileged confused task to
kill otherwise disallowed processes.

Thanks,
Michal

[1] https://lore.kernel.org/r/m1v97x6niq.fsf@xxxxxxxxxxxxxxxxx/