Re: [PATCH 4/8] ucounts: Only except the root user in init_user_ns from RLIMIT_NPROC

On Thu, Feb 10, 2022 at 08:13:20PM -0600, "Eric W. Biederman" ebiederm@xmission.com wrote:

@@ -1881,7 +1881,7 @@ static int do_execveat_common(int fd, struct filename *filename,

[...]

•    (current_user() != INIT_USER) &&
  

•    (current_ucounts() != &init_ucounts) &&
  

[...]

@@ -2027,7 +2027,7 @@ static __latent_entropy struct task_struct *copy_process(

[...]

• if (p->real_cred->user != INIT_USER &&
  

• if ((task_ucounts(p) != &init_ucounts) &&
  

These substitutions make sense to me.

    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
	goto bad_fork_cleanup_count;

} diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 6b2e3ca7ee99..f0c04073403d 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -123,6 +123,8 @@ int create_user_ns(struct cred *new) ns->ucount_max[i] = INT_MAX; } set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC));

• if (new->ucounts == &init_ucounts)

• set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_NPROC, RLIMIT_INFINITY);
  

  set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_MSGQUEUE, rlimit(RLIMIT_MSGQUEUE)); set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_SIGPENDING, rlimit(RLIMIT_SIGPENDING)); set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_MEMLOCK, rlimit(RLIMIT_MEMLOCK));

First, I wanted to object this double fork_init() but I realized it's relevant for newly created user_ns.

Second, I think new->ucounts would be correct at this point and the check should be

if (ucounts == &init_ucounts)

i.e. before set_cred_ucounts() new->ucounts may not be correct.

I'd suggest also a comment in the create_user_ns() explaining the reason is to exempt global root from RLIMINT_NRPOC also indirectly via descendant user_nss.

Thanks, Michal