* [PATCH v3 1/2] keys: Protect key_user lifetime during ownership changes
2026-09-27 16:25 [PATCH v3 0/2] keys: Fix ownership lifetime and accounting races Chengfeng Ye
@ 2026-09-27 16:25 ` Chengfeng Ye
2026-09-27 16:25 ` [PATCH v3 2/2] keys: Serialize ownership transfers with key accounting Chengfeng Ye
1 sibling, 0 replies; 3+ messages in thread
From: Chengfeng Ye @ 2026-09-27 16:25 UTC (permalink / raw)
To: David Howells, Jarkko Sakkinen
Cc: Paul Moore, James Morris, Serge E . Hallyn, keyrings,
linux-security-module, linux-kernel, Chengfeng Ye, stable
keyctl_chown_key() replaces key->user under key->sem and drops the
reference to the previous owner after releasing the semaphore. Readers
which do not hold that semaphore can still be using the previous owner
when key_user_put() frees it.
For example, namespace filtering in /proc/keys can race with chown:
/proc/keys reader keyctl_chown_key()
user = key->user
key->user = newowner
key_user_put(old)
kfree(old)
read user->uid
An earlier instrumented run reported:
BUG: KASAN: slab-use-after-free in proc_keys_start+0x353/0x440
Read of size 4 at addr ffff8881128abbc0 by task poc/88
Call Trace:
proc_keys_start+0x353/0x440
seq_read_iter+0x25d/0x1190
proc_reg_read_iter+0x19e/0x260
Allocated by task 86:
key_user_lookup+0x1b4/0x540
keyctl_chown_key+0x3cc/0xbf0
Freed by task 87:
kfree+0x149/0x330
keyctl_chown_key+0x7b0/0xbf0
Serialize pointer replacement and the affected readers with key_user_lock,
which already protects final key_user removal. Take the lock explicitly
while /proc/keys and find_keyring_by_name() copy the owner's UID. Retain
the quota-owner UID rather than substituting key->uid, since they may
differ for thread keyrings.
Also hold the lock across owner accesses in key_payload_reserve() and
across the instantiated-key count increments. Instantiation need not hold
the target key's semaphore, so these paths need the same lifetime
protection. Leave key-state publication and the chown accounting transfer
outside the new critical sections for the separate accounting fix.
Fixes: 5801649d8b83 ("[PATCH] keys: let keyctl_chown() change a key's owner")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
Changes in v3:
- Split from v2 as patch 1/2; see the cover letter for the full split.
- Rebase onto current mainline and retain explicit reader-side locking.
v2: https://lore.kernel.org/r/20260904080940.575882-1-nicoyip.dev@gmail.com/
security/keys/key.c | 13 +++++++++++--
security/keys/keyctl.c | 2 ++
security/keys/keyring.c | 7 ++++++-
security/keys/proc.c | 15 +++++++++++++--
4 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/security/keys/key.c b/security/keys/key.c
index b34a64d81d47..d0d583194b05 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -21,6 +21,7 @@ struct rb_root key_serial_tree; /* tree of keys indexed by serial */
DEFINE_SPINLOCK(key_serial_lock);
struct rb_root key_user_tree; /* tree of quota records indexed by UID */
+/* Protects key_user_tree and key ownership changes. */
DEFINE_SPINLOCK(key_user_lock);
unsigned int key_quota_root_maxkeys = 1000000; /* root's key count quota */
@@ -380,9 +381,12 @@ int key_payload_reserve(struct key *key, size_t datalen)
/* contemplate the quota adjustment */
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;
+ unsigned int maxbytes;
+
+ spin_lock(&key_user_lock);
+ maxbytes = uid_eq(key->user->uid, GLOBAL_ROOT_UID) ?
+ key_quota_root_maxbytes : key_quota_maxbytes;
spin_lock_irqsave(&key->user->lock, flags);
@@ -396,6 +400,7 @@ int key_payload_reserve(struct key *key, size_t datalen)
key->quotalen += delta;
}
spin_unlock_irqrestore(&key->user->lock, flags);
+ spin_unlock(&key_user_lock);
}
/* change the recorded data length if that didn't generate an error */
@@ -447,7 +452,9 @@ static int __key_instantiate_and_link(struct key *key,
if (ret == 0) {
/* mark the key as being instantiated */
+ spin_lock(&key_user_lock);
atomic_inc(&key->user->nikeys);
+ spin_unlock(&key_user_lock);
mark_key_instantiated(key, 0);
notify_key(key, NOTIFY_KEY_INSTANTIATED, 0);
@@ -604,7 +611,9 @@ int key_reject_and_link(struct key *key,
/* can't instantiate twice */
if (key->state == KEY_IS_UNINSTANTIATED) {
/* mark the key as being negatively instantiated */
+ spin_lock(&key_user_lock);
atomic_inc(&key->user->nikeys);
+ spin_unlock(&key_user_lock);
mark_key_instantiated(key, -error);
notify_key(key, NOTIFY_KEY_INSTANTIATED, -error);
key_set_expiry(key, ktime_get_real_seconds() + timeout);
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index d14ace88e529..c17924609317 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1036,8 +1036,10 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
atomic_inc(&newowner->nikeys);
}
+ spin_lock(&key_user_lock);
zapowner = key->user;
key->user = newowner;
+ spin_unlock(&key_user_lock);
key->uid = uid;
}
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 15bf4af8f282..5943e8b48c0f 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -1148,6 +1148,7 @@ struct key *find_keyring_by_name(const char *name, bool uid_keyring)
{
struct user_namespace *ns = current_user_ns();
struct key *keyring;
+ kuid_t uid;
if (!name)
return ERR_PTR(-EINVAL);
@@ -1158,7 +1159,11 @@ struct key *find_keyring_by_name(const char *name, bool uid_keyring)
* grants Search permission and that hasn't been revoked
*/
list_for_each_entry(keyring, &ns->keyring_name_list, name_link) {
- if (!kuid_has_mapping(ns, keyring->user->uid))
+ spin_lock(&key_user_lock);
+ uid = keyring->user->uid;
+ spin_unlock(&key_user_lock);
+
+ if (!kuid_has_mapping(ns, uid))
continue;
if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
diff --git a/security/keys/proc.c b/security/keys/proc.c
index 4f4e2c1824f1..e507c500c068 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -68,7 +68,13 @@ static struct rb_node *key_serial_next(struct seq_file *p, struct rb_node *n)
n = rb_next(n);
while (n) {
struct key *key = rb_entry(n, struct key, serial_node);
- if (kuid_has_mapping(user_ns, key->user->uid))
+ kuid_t uid;
+
+ spin_lock(&key_user_lock);
+ uid = key->user->uid;
+ spin_unlock(&key_user_lock);
+
+ if (kuid_has_mapping(user_ns, uid))
break;
n = rb_next(n);
}
@@ -80,6 +86,7 @@ static struct key *find_ge_key(struct seq_file *p, key_serial_t id)
struct user_namespace *user_ns = seq_user_ns(p);
struct rb_node *n = key_serial_tree.rb_node;
struct key *minkey = NULL;
+ kuid_t uid;
while (n) {
struct key *key = rb_entry(n, struct key, serial_node);
@@ -100,7 +107,11 @@ static struct key *find_ge_key(struct seq_file *p, key_serial_t id)
return NULL;
for (;;) {
- if (kuid_has_mapping(user_ns, minkey->user->uid))
+ spin_lock(&key_user_lock);
+ uid = minkey->user->uid;
+ spin_unlock(&key_user_lock);
+
+ if (kuid_has_mapping(user_ns, uid))
return minkey;
n = rb_next(&minkey->serial_node);
if (!n)
--
2.43.0
^ permalink raw reply [flat|nested] 3+ messages in thread* [PATCH v3 2/2] keys: Serialize ownership transfers with key accounting
2026-09-27 16:25 [PATCH v3 0/2] keys: Fix ownership lifetime and accounting races Chengfeng Ye
2026-09-27 16:25 ` [PATCH v3 1/2] keys: Protect key_user lifetime during ownership changes Chengfeng Ye
@ 2026-09-27 16:25 ` Chengfeng Ye
1 sibling, 0 replies; 3+ messages in thread
From: Chengfeng Ye @ 2026-09-27 16:25 UTC (permalink / raw)
To: David Howells, Jarkko Sakkinen
Cc: Paul Moore, James Morris, Serge E . Hallyn, keyrings,
linux-security-module, linux-kernel, Chengfeng Ye, stable
Protecting individual accesses to key->user does not make ownership
transfers atomic with accounting updates. keyctl_chown_key() holds
key->sem, but instantiation is serialized by key_construction_mutex and
need not hold that semaphore. KEY_LOOKUP_PARTIAL also permits chown of
an uninstantiated key.
The instantiated-key count can therefore be charged to the wrong owner:
instantiate keyctl_chown_key()
lock key_user_lock
increment old->nikeys
unlock key_user_lock
observe KEY_IS_UNINSTANTIATED
skip the nikeys transfer
replace key->user
mark key instantiated
The key becomes instantiated under the new owner while the increment
remains with the old owner. Negative instantiation has the same race.
Quota reservation can likewise run between charging the new owner and
replacing key->user. It then adjusts the old owner's quota and changes
key->quotalen while chown is transferring that quota burden.
Extend the key_user_lock critical section in keyctl_chown_key() across
the quota and key-count transfers, state check, and owner replacement.
Also extend the instantiation critical sections across the state update,
so chown observes the count increment and instantiated state together.
The existing per-user quota locks continue to serialize quota changes
against other keys owned by the same user.
Keep allocations, notifications and reference release outside
key_user_lock, and release it on the quota-overrun path.
Fixes: 5801649d8b83 ("[PATCH] keys: let keyctl_chown() change a key's owner")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
Changes in v3:
- Split from v2 as patch 2/2; see the cover letter for the full split.
- Rebase onto current mainline and retain explicit reader-side locking.
v2: https://lore.kernel.org/r/20260904080940.575882-1-nicoyip.dev@gmail.com/
security/keys/key.c | 4 ++--
security/keys/keyctl.c | 6 ++++--
2 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/security/keys/key.c b/security/keys/key.c
index d0d583194b05..54c675b3b58d 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -454,8 +454,8 @@ static int __key_instantiate_and_link(struct key *key,
/* mark the key as being instantiated */
spin_lock(&key_user_lock);
atomic_inc(&key->user->nikeys);
- spin_unlock(&key_user_lock);
mark_key_instantiated(key, 0);
+ spin_unlock(&key_user_lock);
notify_key(key, NOTIFY_KEY_INSTANTIATED, 0);
if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
@@ -613,8 +613,8 @@ int key_reject_and_link(struct key *key,
/* mark the key as being negatively instantiated */
spin_lock(&key_user_lock);
atomic_inc(&key->user->nikeys);
- spin_unlock(&key_user_lock);
mark_key_instantiated(key, -error);
+ spin_unlock(&key_user_lock);
notify_key(key, NOTIFY_KEY_INSTANTIATED, -error);
key_set_expiry(key, ktime_get_real_seconds() + timeout);
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index c17924609317..83a9575b084e 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1004,6 +1004,8 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
if (!newowner)
goto error_put;
+ spin_lock(&key_user_lock);
+
/* transfer the quota burden to the new user */
if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
unsigned maxkeys = uid_eq(uid, GLOBAL_ROOT_UID) ?
@@ -1036,11 +1038,10 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
atomic_inc(&newowner->nikeys);
}
- spin_lock(&key_user_lock);
zapowner = key->user;
key->user = newowner;
- spin_unlock(&key_user_lock);
key->uid = uid;
+ spin_unlock(&key_user_lock);
}
/* change the GID */
@@ -1060,6 +1061,7 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
quota_overrun:
spin_unlock_irqrestore(&newowner->lock, flags);
+ spin_unlock(&key_user_lock);
zapowner = newowner;
ret = -EDQUOT;
goto error_put;
--
2.43.0
^ permalink raw reply [flat|nested] 3+ messages in thread