[Devel] [PATCH vz9] ucounts: Fix ucount incr/decr when uid is changed without changing the underlying user_struct

[Nikolay Borisov]

When preforming setuid the general expectation is that the underlying
user_struct will also be changed. However, in our kernels this doesn't
hold true to the presence of ff716deacf0c ("userns: associate user_struct
with the user_namespace").

Running userns08 testcase from ltp causes a warning to be triggered
when decrementing NPROC count on process reap. The reason for the
warning is when the uid is changed the relevant code in commit_cred()
is supposed to adjust the ucounts for the old (pre-setuid) and new
(after setuid) state. However, the ceck in the upstream kernel only
triggers if userns or user_struct have changed. Fix the issue by
augmenting the check to ensure NPROC is adjusted when just the uid is
changed.

https://jira.sw.ru/browse/PSBM-145641
Signed-off-by: Nikolay Borisov <nikolay.borisov at virtuozzo.com>
---
 kernel/cred.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/cred.c b/kernel/cred.c
index 96466cc1c527..7dedd97a27c2 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -395,6 +395,9 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 #endif

 	p->cred = p->real_cred = get_cred(new);
+	trace_printk("incr rlim for ns: %u val: %ld uid: %u euid: %u ucounts: %p\n", task_ucounts(p)->ns->ns.inum,
+		     atomic_long_read(&task_ucounts(p)->ucount[UCOUNT_RLIMIT_NPROC]),
+		     task_uid(p).val, task_euid(p).val, task_ucounts(p));
 	inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 	alter_cred_subscribers(new, 2);
 	validate_creds(new);
@@ -495,12 +498,21 @@ int commit_creds(struct cred *new)
 	 * in set_user().
 	 */
 	alter_cred_subscribers(new, 2);
-	if (new->user != old->user || new->user_ns != old->user_ns)
+	trace_printk("User adjustment\n");
+	if (new->user != old->user || new->user_ns != old->user_ns || !uid_eq(new->uid, old->uid)) {
+		trace_printk("incr rlim for ns: %u val: %ld nuid: %u ouid: %u new ucount: %p old ucount: %p\n", new->ucounts->ns->ns.inum,
+			     atomic_long_read(&new->ucounts->ucount[UCOUNT_RLIMIT_NPROC]), __kuid_val(new->uid), __kuid_val(old->uid),
+			     new->ucounts, old->ucounts);
+
 		inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
+	}
 	rcu_assign_pointer(task->real_cred, new);
 	rcu_assign_pointer(task->cred, new);
-	if (new->user != old->user || new->user_ns != old->user_ns)
+	if (new->user != old->user || new->user_ns != old->user_ns || !uid_eq(new->uid, old->uid) ) {
+		trace_printk("decr rlim for ns: %u val: %ld\n", old->ucounts->ns->ns.inum,
+			     atomic_long_read(&old->ucounts->ucount[UCOUNT_RLIMIT_NPROC]));
 		dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
+	}
 	alter_cred_subscribers(old, -2);

 	/* send notifications */
--
2.34.1