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, 8 insertions, 0 deletions

diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index e3d79a7b6db6..b5d5333ab330 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -918,6 +918,13 @@ void key_change_session_keyring(struct callback_head *twork)
 		return;
 	}
 
+	/* If get_ucounts fails more bits are needed in the refcount */
+	if (unlikely(!get_ucounts(old->ucounts))) {
+		WARN_ONCE(1, "In %s get_ucounts failed\n", __func__);
+		put_cred(new);
+		return;
+	}
+
 	new->  uid	= old->  uid;
 	new-> euid	= old-> euid;
 	new-> suid	= old-> suid;
@@ -927,6 +934,7 @@ void key_change_session_keyring(struct callback_head *twork)
 	new-> sgid	= old-> sgid;
 	new->fsgid	= old->fsgid;
 	new->user	= get_uid(old->user);
+	new->ucounts	= old->ucounts;
 	new->user_ns	= get_user_ns(old->user_ns);
 	new->group_info	= get_group_info(old->group_info);