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Message-Id: <20250402085257.728844-1-jarkko@kernel.org>
Date: Wed, 2 Apr 2025 11:52:57 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: David Howells <dhowells@...hat.com>
Cc: keyrings@...r.kernel.org,
Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>,
Jarkko Sakkinen <jarkko@...nel.org>,
Paul Moore <paul@...l-moore.com>,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org
Subject: [RFC PATCH v3] KEYS: Add a list for unreferenced keys
From: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
Add an isolated list for unreferenced keys, thereby splitting key
deletion as separate phase, after the reaping cycle. This makes the
whole process more safe, as these two distinct tasks don't intervene
each other. As an effect, KEY_FLAG_FINAL_PUT is no longer needed.
Since `security/keys/proc.c` reserves key_serial_lock for variable
amount of time, `rb_erase()` cannot be done within `key_put()` by using
IRQ saving/restoring versions of the spin lock functions. For the same
reason, the key needs to co-exist both in the tree and in the list for
period of time.
Therefore, split the union in `struct key` into separate `serial_node`
and `graveyard_link` fields, and introduce a separate lock for the
graveyard, which is locked and unlocked using IRQ saving/restoring
versions of the locking routines.
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
---
v3:
- Using spin_lock() fails since key_put() is executed inside IRQs.
Using spin_lock_irqsave() would neither work given the lock is
acquired for /proc/keys. Therefore, separate the lock for
graveyard and key_graveyard before reaping key_serial_tree.
v2:
- Rename key_gc_unused_keys as key_gc_graveyard, and re-document the
function.
---
include/linux/key.h | 7 ++-----
security/keys/gc.c | 34 ++++++++++++++--------------------
security/keys/internal.h | 2 ++
security/keys/key.c | 7 +++++--
4 files changed, 23 insertions(+), 27 deletions(-)
diff --git a/include/linux/key.h b/include/linux/key.h
index ba05de8579ec..c50659184bdf 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -195,10 +195,8 @@ enum key_state {
struct key {
refcount_t usage; /* number of references */
key_serial_t serial; /* key serial number */
- union {
- struct list_head graveyard_link;
- struct rb_node serial_node;
- };
+ struct list_head graveyard_link; /* key->usage == 0 */
+ struct rb_node serial_node;
#ifdef CONFIG_KEY_NOTIFICATIONS
struct watch_list *watchers; /* Entities watching this key for changes */
#endif
@@ -236,7 +234,6 @@ struct key {
#define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */
#define KEY_FLAG_KEEP 8 /* set if key should not be removed */
#define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */
-#define KEY_FLAG_FINAL_PUT 10 /* set if final put has happened on key */
/* the key type and key description string
* - the desc is used to match a key against search criteria
diff --git a/security/keys/gc.c b/security/keys/gc.c
index f27223ea4578..7b1356c1095d 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -130,9 +130,9 @@ void key_gc_keytype(struct key_type *ktype)
}
/*
- * Garbage collect a list of unreferenced, detached keys
+ * Takes ownership of the given list, and deinitializes and destroys the keys.
*/
-static noinline void key_gc_unused_keys(struct list_head *keys)
+static noinline void key_gc_graveyard(struct list_head *keys)
{
while (!list_empty(keys)) {
struct key *key =
@@ -206,6 +206,17 @@ static void key_garbage_collector(struct work_struct *work)
new_timer = TIME64_MAX;
+ spin_lock_irqsave(&key_graveyard_lock, flags);
+ list_splice_init(&key_graveyard, &graveyard);
+ spin_unlock_irqrestore(&key_graveyard_lock, flags);
+
+ list_for_each_entry(key, &graveyard, graveyard_link) {
+ spin_lock(&key_serial_lock);
+ kdebug("unrefd key %d", key->serial);
+ rb_erase(&key->serial_node, &key_serial_tree);
+ spin_unlock(&key_serial_lock);
+ }
+
/* As only this function is permitted to remove things from the key
* serial tree, if cursor is non-NULL then it will always point to a
* valid node in the tree - even if lock got dropped.
@@ -218,11 +229,6 @@ static void key_garbage_collector(struct work_struct *work)
key = rb_entry(cursor, struct key, serial_node);
cursor = rb_next(cursor);
- if (test_bit(KEY_FLAG_FINAL_PUT, &key->flags)) {
- smp_mb(); /* Clobber key->user after FINAL_PUT seen. */
- goto found_unreferenced_key;
- }
-
if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {
if (key->type == key_gc_dead_keytype) {
gc_state |= KEY_GC_FOUND_DEAD_KEY;
@@ -299,7 +305,7 @@ static void key_garbage_collector(struct work_struct *work)
if (!list_empty(&graveyard)) {
kdebug("gc keys");
- key_gc_unused_keys(&graveyard);
+ key_gc_graveyard(&graveyard);
}
if (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 |
@@ -328,18 +334,6 @@ static void key_garbage_collector(struct work_struct *work)
kleave(" [end %x]", gc_state);
return;
- /* We found an unreferenced key - once we've removed it from the tree,
- * we can safely drop the lock.
- */
-found_unreferenced_key:
- kdebug("unrefd key %d", key->serial);
- rb_erase(&key->serial_node, &key_serial_tree);
- spin_unlock(&key_serial_lock);
-
- list_add_tail(&key->graveyard_link, &graveyard);
- gc_state |= KEY_GC_REAP_AGAIN;
- goto maybe_resched;
-
/* We found a restricted keyring and need to update the restriction if
* it is associated with the dead key type.
*/
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 2cffa6dc8255..08f356d04d78 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -66,6 +66,8 @@ struct key_user {
extern struct rb_root key_user_tree;
extern spinlock_t key_user_lock;
extern struct key_user root_key_user;
+extern struct list_head key_graveyard;
+extern spinlock_t key_graveyard_lock;
extern struct key_user *key_user_lookup(kuid_t uid);
extern void key_user_put(struct key_user *user);
diff --git a/security/keys/key.c b/security/keys/key.c
index 7198cd2ac3a3..7511f2017b6b 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -22,6 +22,8 @@ DEFINE_SPINLOCK(key_serial_lock);
struct rb_root key_user_tree; /* tree of quota records indexed by UID */
DEFINE_SPINLOCK(key_user_lock);
+LIST_HEAD(key_graveyard);
+DEFINE_SPINLOCK(key_graveyard_lock);
unsigned int key_quota_root_maxkeys = 1000000; /* root's key count quota */
unsigned int key_quota_root_maxbytes = 25000000; /* root's key space quota */
@@ -658,8 +660,9 @@ void key_put(struct key *key)
key->user->qnbytes -= key->quotalen;
spin_unlock_irqrestore(&key->user->lock, flags);
}
- smp_mb(); /* key->user before FINAL_PUT set. */
- set_bit(KEY_FLAG_FINAL_PUT, &key->flags);
+ spin_lock_irqsave(&key_graveyard_lock, flags);
+ list_add_tail(&key->graveyard_link, &key_graveyard);
+ spin_unlock_irqrestore(&key_graveyard_lock, flags);
schedule_work(&key_gc_work);
}
}
--
2.39.5
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