Merge branch 'ucount-fixes-for-v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull ucounts fixes from Eric Biederman:
 "There has been one very hard to track down bug in the ucount code that
  we have been tracking since roughly v5.14 was released. Alex managed
  to find a reliable reproducer a few days ago and then I was able to
  instrument the code and figure out what the issue was.

  It turns out the sigqueue_alloc single atomic operation optimization
  did not play nicely with ucounts multiple level rlimits. It turned out
  that either sigqueue_alloc or sigqueue_free could be operating on
  multiple levels and trigger the conditions for the optimization on
  more than one level at the same time.

  To deal with that situation I have introduced inc_rlimit_get_ucounts
  and dec_rlimit_put_ucounts that just focuses on the optimization and
  the rlimit and ucount changes.

  While looking into the big bug I found I couple of other little issues
  so I am including those fixes here as well.

  When I have time I would very much like to dig into process ownership
  of the shared signal queue and see if we could pick a single owner for
  the entire queue so that all of the rlimits can count to that owner.
  That should entirely remove the need to call get_ucounts and
  put_ucounts in sigqueue_alloc and sigqueue_free. It is difficult
  because Linux unlike POSIX supports setuid that works on a single
  thread"

* 'ucount-fixes-for-v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  ucounts: Move get_ucounts from cred_alloc_blank to key_change_session_keyring
  ucounts: Proper error handling in set_cred_ucounts
  ucounts: Pair inc_rlimit_ucounts with dec_rlimit_ucoutns in commit_creds
  ucounts: Fix signal ucount refcounting

1 files changed, 6 insertions, 19 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 952741f6d0f9f..487bf4f5dadf4 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -426,22 +426,10 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags,
 	 */
 	rcu_read_lock();
 	ucounts = task_ucounts(t);
-	sigpending = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1);
-	switch (sigpending) {
-	case 1:
-		if (likely(get_ucounts(ucounts)))
-			break;
-		fallthrough;
-	case LONG_MAX:
-		/*
-		 * we need to decrease the ucount in the userns tree on any
-		 * failure to avoid counts leaking.
-		 */
-		dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1);
-		rcu_read_unlock();
-		return NULL;
-	}
+	sigpending = inc_rlimit_get_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING);
 	rcu_read_unlock();
+	if (!sigpending)
+		return NULL;
 
 	if (override_rlimit || likely(sigpending <= task_rlimit(t, RLIMIT_SIGPENDING))) {
 		q = kmem_cache_alloc(sigqueue_cachep, gfp_flags);
@@ -450,8 +438,7 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags,
 	}
 
 	if (unlikely(q == NULL)) {
-		if (dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1))
-			put_ucounts(ucounts);
+		dec_rlimit_put_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING);
 	} else {
 		INIT_LIST_HEAD(&q->list);
 		q->flags = sigqueue_flags;
@@ -464,8 +451,8 @@ static void __sigqueue_free(struct sigqueue *q)
 {
 	if (q->flags & SIGQUEUE_PREALLOC)
 		return;
-	if (q->ucounts && dec_rlimit_ucounts(q->ucounts, UCOUNT_RLIMIT_SIGPENDING, 1)) {
-		put_ucounts(q->ucounts);
+	if (q->ucounts) {
+		dec_rlimit_put_ucounts(q->ucounts, UCOUNT_RLIMIT_SIGPENDING);
 		q->ucounts = NULL;
 	}
 	kmem_cache_free(sigqueue_cachep, q);