On Mon, Sep 18, 2023 at 12:52 PM Christian Brauner [off-list ref] wrote:

On Sun, Sep 17, 2023 at 04:32:04PM +0200, Miklos Szeredi wrote:

quoted

On Sun, Sep 17, 2023 at 2:54 AM Matthew House [off-list ref] wrote:

quoted

quoted

+       list_for_each_entry(r, &m->mnt_mounts, mnt_child) {
+               if (!capable(CAP_SYS_ADMIN) &&

quoted

Good point.  That issue was nagging at the back of my mind.  Having an
explicit flag nicely solves the issue.

Ideally we avoid multiple capable(CAP_SYS_ADMIN) calls by only doing it
once and saving the return value. capable() call's aren't that cheap.

Agreed.  The capability check doesn't do any subject/object
comparisons so calling it for each mount is overkill.  However, I
would think we would want the LSM hook called from inside the loop as
that could involve a subject (@current) and object (individual mount
point) comparison.

Plus, we should decide whether this should trigger an audit event or
not: capable(CAP_SYS_ADMIN) triggers an audit event,
ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN) wouldn't.

Why would we not want to audit the capable() call?

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