Merge branch 'ucount-fixes-for-v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull ucount cleanups from Eric Biederman:
 "While working on the ucount fixes a for v5.15 a number of cleanups
  suggested themselves.

  Little things like not testing for NULL when a pointer can not be NULL
  and wrapping atomic_add_negative with a more descriptive name, so that
  people reading the code can more quickly understand what is going on"

* 'ucount-fixes-for-v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  ucounts: Use atomic_long_sub_return for clarity
  ucounts: Add get_ucounts_or_wrap for clarity
  ucounts: Remove unnecessary test for NULL ucount in get_ucounts
  ucounts: In set_cred_ucounts assume new->ucounts is non-NULL

Author: torvalds

kernel/cred.c

@@ -676,15 +676,14 @@ int set_cred_ucounts(struct cred *new)
 	 * This optimization is needed because alloc_ucounts() uses locks
 	 * for table lookups.
 	 */
-	if (old_ucounts && old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
+	if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
 		return 0;
 
 	if (!(new_ucounts = alloc_ucounts(new->user_ns, new->euid)))
 		return -EAGAIN;
 
 	new->ucounts = new_ucounts;
-	if (old_ucounts)
-		put_ucounts(old_ucounts);
+	put_ucounts(old_ucounts);
 
 	return 0;
 }

kernel/ucount.c

@@ -150,9 +150,15 @@ static void hlist_add_ucounts(struct ucounts *ucounts)
 	spin_unlock_irq(&ucounts_lock);
 }
 
+static inline bool get_ucounts_or_wrap(struct ucounts *ucounts)
+{
+	/* Returns true on a successful get, false if the count wraps. */
+	return !atomic_add_negative(1, &ucounts->count);
+}
+
 struct ucounts *get_ucounts(struct ucounts *ucounts)
 {
-	if (ucounts && atomic_add_negative(1, &ucounts->count)) {
+	if (!get_ucounts_or_wrap(ucounts)) {
 		put_ucounts(ucounts);
 		ucounts = NULL;
 	}
@@ -163,7 +169,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
 	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
 	struct ucounts *ucounts, *new;
-	long overflow;
+	bool wrapped;
 
 	spin_lock_irq(&ucounts_lock);
 	ucounts = find_ucounts(ns, uid, hashent);
@@ -188,9 +194,9 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 			return new;
 		}
 	}
-	overflow = atomic_add_negative(1, &ucounts->count);
+	wrapped = !get_ucounts_or_wrap(ucounts);
 	spin_unlock_irq(&ucounts_lock);
-	if (overflow) {
+	if (wrapped) {
 		put_ucounts(ucounts);
 		return NULL;
 	}
@@ -276,7 +282,7 @@ bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
 	struct ucounts *iter;
 	long new = -1; /* Silence compiler warning */
 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
-		long dec = atomic_long_add_return(-v, &iter->ucount[type]);
+		long dec = atomic_long_sub_return(v, &iter->ucount[type]);
 		WARN_ON_ONCE(dec < 0);
 		if (iter == ucounts)
 			new = dec;
@@ -289,7 +295,7 @@ static void do_dec_rlimit_put_ucounts(struct ucounts *ucounts,
 {
 	struct ucounts *iter, *next;
 	for (iter = ucounts; iter != last; iter = next) {
-		long dec = atomic_long_add_return(-1, &iter->ucount[type]);
+		long dec = atomic_long_sub_return(1, &iter->ucount[type]);
 		WARN_ON_ONCE(dec < 0);
 		next = iter->ns->ucounts;
 		if (dec == 0)
@@ -326,7 +332,7 @@ long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum ucount_type type)
 	}
 	return ret;
 dec_unwind:
-	dec = atomic_long_add_return(-1, &iter->ucount[type]);
+	dec = atomic_long_sub_return(1, &iter->ucount[type]);
 	WARN_ON_ONCE(dec < 0);
 unwind:
 	do_dec_rlimit_put_ucounts(ucounts, iter, type);