[PATCH] keys: Fix key_user use-after-free during ownership changes
From: Chengfeng Ye <hidden>
Date: 2026-08-23 17:05:01
Also in:
keyrings, lkml
Subsystem:
keys/keyrings, security subsystem, the rest · Maintainers:
David Howells, Jarkko Sakkinen, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
keyctl_chown_key() replaces key->user while holding key->sem and drops
the old key_user reference after releasing the semaphore. The /proc/keys
iterators and find_keyring_by_name() instead dereference key->user while
holding unrelated locks.
This allows the following interleaving:
CPU 0 (/proc/keys) CPU 1 (KEYCTL_CHOWN)
load old key->user
replace key->user
key_user_put(old)
kfree(old)
read old->uid
Serialize the namespace-mapping reads and the pointer replacement with
key_user_lock. This lock already protects final key_user removal, so the
old object cannot be freed while its uid is being read. Keep reading the
quota-owner UID rather than key->uid because those values can legitimately
differ for thread keyrings.
Fixes: 454804ab0302 ("keys: make procfiles per-user-namespace")
Signed-off-by: Chengfeng Ye <redacted>
---
security/keys/internal.h | 10 ++++++++++
security/keys/keyctl.c | 2 ++
security/keys/keyring.c | 2 +-
security/keys/proc.c | 4 ++--
4 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/security/keys/internal.h b/security/keys/internal.h
index b7b622bc36a1..741d547ba5c4 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h@@ -70,6 +70,16 @@ extern struct key_user root_key_user; extern struct key_user *key_user_lookup(kuid_t uid); extern void key_user_put(struct key_user *user); +static inline kuid_t key_user_uid(const struct key *key) +{ + kuid_t uid; + + spin_lock(&key_user_lock); + uid = key->user->uid; + spin_unlock(&key_user_lock); + return uid; +} + /* * Key quota limits. * - root has its own separate limits to everyone else
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..49f4be934525 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c@@ -1158,7 +1158,7 @@ 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)) + if (!kuid_has_mapping(ns, key_user_uid(keyring))) continue; if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
diff --git a/security/keys/proc.c b/security/keys/proc.c
index 4f4e2c1824f1..8d6d26652aab 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c@@ -68,7 +68,7 @@ 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)) + if (kuid_has_mapping(user_ns, key_user_uid(key))) break; n = rb_next(n); }
@@ -100,7 +100,7 @@ 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)) + if (kuid_has_mapping(user_ns, key_user_uid(minkey))) return minkey; n = rb_next(&minkey->serial_node); if (!n)
--
2.43.0