[PATCH v3] keys: update key quotas in key_put()

[Luis Henriques]

Delaying key quotas update when key's refcount reaches 0 in key_put() has
been causing some issues in fscrypt testing, specifically in fstest
generic/581.  This commit fixes this test flakiness by dealing with the
quotas immediately, and leaving all the other clean-ups to the key garbage
collector.

This is done by moving the updates to the qnkeys and qnbytes fields in
struct key_user from key_gc_unused_keys() into key_put().  Unfortunately,
this also means that we need to switch to the irq-version of the spinlock
that protects these fields and use spin_lock_{irqsave,irqrestore} in all the
code that touches these fields.

Signed-off-by: Luis Henriques <lhenriques@xxxxxxx>
---
Changes since v2:
- Updated commit message as suggested by Jarkko, adding details on the
  implementation

 security/keys/gc.c     |  8 --------
 security/keys/key.c    | 32 ++++++++++++++++++++++----------
 security/keys/keyctl.c | 11 ++++++-----
 3 files changed, 28 insertions(+), 23 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index eaddaceda14e..7d687b0962b1 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -155,14 +155,6 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
 
 		security_key_free(key);
 
-		/* deal with the user's key tracking and quota */
-		if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
-			spin_lock(&key->user->lock);
-			key->user->qnkeys--;
-			key->user->qnbytes -= key->quotalen;
-			spin_unlock(&key->user->lock);
-		}
-
 		atomic_dec(&key->user->nkeys);
 		if (state != KEY_IS_UNINSTANTIATED)
 			atomic_dec(&key->user->nikeys);
diff --git a/security/keys/key.c b/security/keys/key.c
index 5b10641debd5..ec155cfaae38 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -231,6 +231,7 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 	struct key *key;
 	size_t desclen, quotalen;
 	int ret;
+	unsigned long irqflags;
 
 	key = ERR_PTR(-EINVAL);
 	if (!desc || !*desc)
@@ -260,7 +261,7 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 		unsigned maxbytes = uid_eq(uid, GLOBAL_ROOT_UID) ?
 			key_quota_root_maxbytes : key_quota_maxbytes;
 
-		spin_lock(&user->lock);
+		spin_lock_irqsave(&user->lock, irqflags);
 		if (!(flags & KEY_ALLOC_QUOTA_OVERRUN)) {
 			if (user->qnkeys + 1 > maxkeys ||
 			    user->qnbytes + quotalen > maxbytes ||
@@ -270,7 +271,7 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 
 		user->qnkeys++;
 		user->qnbytes += quotalen;
-		spin_unlock(&user->lock);
+		spin_unlock_irqrestore(&user->lock, irqflags);
 	}
 
 	/* allocate and initialise the key and its description */
@@ -328,10 +329,10 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 	kfree(key->description);
 	kmem_cache_free(key_jar, key);
 	if (!(flags & KEY_ALLOC_NOT_IN_QUOTA)) {
-		spin_lock(&user->lock);
+		spin_lock_irqsave(&user->lock, irqflags);
 		user->qnkeys--;
 		user->qnbytes -= quotalen;
-		spin_unlock(&user->lock);
+		spin_unlock_irqrestore(&user->lock, irqflags);
 	}
 	key_user_put(user);
 	key = ERR_PTR(ret);
@@ -341,10 +342,10 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 	kmem_cache_free(key_jar, key);
 no_memory_2:
 	if (!(flags & KEY_ALLOC_NOT_IN_QUOTA)) {
-		spin_lock(&user->lock);
+		spin_lock_irqsave(&user->lock, irqflags);
 		user->qnkeys--;
 		user->qnbytes -= quotalen;
-		spin_unlock(&user->lock);
+		spin_unlock_irqrestore(&user->lock, irqflags);
 	}
 	key_user_put(user);
 no_memory_1:
@@ -352,7 +353,7 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 	goto error;
 
 no_quota:
-	spin_unlock(&user->lock);
+	spin_unlock_irqrestore(&user->lock, irqflags);
 	key_user_put(user);
 	key = ERR_PTR(-EDQUOT);
 	goto error;
@@ -381,8 +382,9 @@ int key_payload_reserve(struct key *key, size_t datalen)
 	if (delta != 0 && test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
 		unsigned maxbytes = uid_eq(key->user->uid, GLOBAL_ROOT_UID) ?
 			key_quota_root_maxbytes : key_quota_maxbytes;
+		unsigned long flags;
 
-		spin_lock(&key->user->lock);
+		spin_lock_irqsave(&key->user->lock, flags);
 
 		if (delta > 0 &&
 		    (key->user->qnbytes + delta > maxbytes ||
@@ -393,7 +395,7 @@ int key_payload_reserve(struct key *key, size_t datalen)
 			key->user->qnbytes += delta;
 			key->quotalen += delta;
 		}
-		spin_unlock(&key->user->lock);
+		spin_unlock_irqrestore(&key->user->lock, flags);
 	}
 
 	/* change the recorded data length if that didn't generate an error */
@@ -646,8 +648,18 @@ void key_put(struct key *key)
 	if (key) {
 		key_check(key);
 
-		if (refcount_dec_and_test(&key->usage))
+		if (refcount_dec_and_test(&key->usage)) {
+			unsigned long flags;
+
+			/* deal with the user's key tracking and quota */
+			if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
+				spin_lock_irqsave(&key->user->lock, flags);
+				key->user->qnkeys--;
+				key->user->qnbytes -= key->quotalen;
+				spin_unlock_irqrestore(&key->user->lock, flags);
+			}
 			schedule_work(&key_gc_work);
+		}
 	}
 }
 EXPORT_SYMBOL(key_put);
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 10ba439968f7..4bc3e9398ee3 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -954,6 +954,7 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
 	long ret;
 	kuid_t uid;
 	kgid_t gid;
+	unsigned long flags;
 
 	uid = make_kuid(current_user_ns(), user);
 	gid = make_kgid(current_user_ns(), group);
@@ -1010,7 +1011,7 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
 			unsigned maxbytes = uid_eq(uid, GLOBAL_ROOT_UID) ?
 				key_quota_root_maxbytes : key_quota_maxbytes;
 
-			spin_lock(&newowner->lock);
+			spin_lock_irqsave(&newowner->lock, flags);
 			if (newowner->qnkeys + 1 > maxkeys ||
 			    newowner->qnbytes + key->quotalen > maxbytes ||
 			    newowner->qnbytes + key->quotalen <
@@ -1019,12 +1020,12 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
 
 			newowner->qnkeys++;
 			newowner->qnbytes += key->quotalen;
-			spin_unlock(&newowner->lock);
+			spin_unlock_irqrestore(&newowner->lock, flags);
 
-			spin_lock(&key->user->lock);
+			spin_lock_irqsave(&key->user->lock, flags);
 			key->user->qnkeys--;
 			key->user->qnbytes -= key->quotalen;
-			spin_unlock(&key->user->lock);
+			spin_unlock_irqrestore(&key->user->lock, flags);
 		}
 
 		atomic_dec(&key->user->nkeys);
@@ -1056,7 +1057,7 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
 	return ret;
 
 quota_overrun:
-	spin_unlock(&newowner->lock);
+	spin_unlock_irqrestore(&newowner->lock, flags);
 	zapowner = newowner;
 	ret = -EDQUOT;
 	goto error_put;