queue-7.2/keys-finalize-persistent-keyring-timeout-after-link-attempt.patch

From 25bf14f817168079f731975b8998fc2af380f29e Mon Sep 17 00:00:00 2001
From: Karl Mehltretter <kmehltretter@gmail.com>
Date: Sat, 12 Sep 2026 11:54:40 +0200
Subject: keys: finalize persistent keyring timeout after link attempt

From: Karl Mehltretter <kmehltretter@gmail.com>

commit 25bf14f817168079f731975b8998fc2af380f29e upstream.

When no keyring exists for the requested UID, KEYCTL_GET_PERSISTENT
creates and registers one before linking it to the requested destination.
The configured timeout is set only after the destination link succeeds.

A destination restricted with KEYCTL_RESTRICT_KEYRING makes that link fail
with -EPERM. With persistent_keyring_expiry set to 60 seconds, /proc/keys
still reports the registered keyring's expiry as "perm".
The failed call therefore leaves a quota-exempt keyring in the namespace's
hidden register, where it may remain until namespace teardown.

Rename the write-locked helper to key_get_or_create_persistent() and return
the key reference through a result parameter. Return 0 when it creates a
keyring and 1 when the retry finds an existing one. Return a negative error
on failure. Another caller may create the keyring between the initial
read-locked lookup and the retry under the write lock.

Set the timeout after permission checking and linking. Do this on success,
or on failure if the call allocated the keyring. This leaves a new keyring
collectible after failure without starting its timeout while linking is
still in progress.

Cc: stable@vger.kernel.org # v5.10+
Fixes: f36f8c75ae2e ("KEYS: Add per-user_namespace registers for persistent per-UID kerberos caches")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Link: https://lore.kernel.org/r/20260912095440.79864-1-kmehltretter@gmail.com
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 security/keys/persistent.c |   55 ++++++++++++++++++++++++++-------------------
 1 file changed, 32 insertions(+), 23 deletions(-)

--- a/security/keys/persistent.c
+++ b/security/keys/persistent.c
@@ -33,25 +33,31 @@ static int key_create_persistent_registe
 }
 
 /*
- * Create the persistent keyring for the specified user.
+ * Get or create the persistent keyring for the specified user.
  *
  * Called with the namespace's sem locked for writing.
+ *
+ * Returns a boolean indicating whether the keyring already existed,
+ * or a negative error. On success, *persistent_ref holds a reference
+ * to the keyring.
  */
-static key_ref_t key_create_persistent(struct user_namespace *ns, kuid_t uid,
-				       struct keyring_index_key *index_key)
+static int key_get_or_create_persistent(struct user_namespace *ns, kuid_t uid,
+					struct keyring_index_key *index_key,
+					key_ref_t *persistent_ref)
 {
 	struct key *persistent;
-	key_ref_t reg_ref, persistent_ref;
+	key_ref_t reg_ref;
 
 	if (!ns->persistent_keyring_register) {
-		long err = key_create_persistent_register(ns);
+		int err = key_create_persistent_register(ns);
+
 		if (err < 0)
-			return ERR_PTR(err);
+			return err;
 	} else {
 		reg_ref = make_key_ref(ns->persistent_keyring_register, true);
-		persistent_ref = find_key_to_update(reg_ref, index_key);
-		if (persistent_ref)
-			return persistent_ref;
+		*persistent_ref = find_key_to_update(reg_ref, index_key);
+		if (*persistent_ref)
+			return 1;
 	}
 
 	persistent = keyring_alloc(index_key->description,
@@ -61,9 +67,10 @@ static key_ref_t key_create_persistent(s
 				   KEY_ALLOC_NOT_IN_QUOTA, NULL,
 				   ns->persistent_keyring_register);
 	if (IS_ERR(persistent))
-		return ERR_CAST(persistent);
+		return PTR_ERR(persistent);
 
-	return make_key_ref(persistent, true);
+	*persistent_ref = make_key_ref(persistent, true);
+	return 0;
 }
 
 /*
@@ -78,6 +85,7 @@ static long key_get_persistent(struct us
 	key_ref_t reg_ref, persistent_ref;
 	char buf[32];
 	long ret;
+	bool created = false;
 
 	/* Look in the register if it exists */
 	memset(&index_key, 0, sizeof(index_key));
@@ -100,23 +108,24 @@ static long key_get_persistent(struct us
 	 * also need to create the register.
 	 */
 	down_write(&ns->keyring_sem);
-	persistent_ref = key_create_persistent(ns, uid, &index_key);
+	ret = key_get_or_create_persistent(ns, uid, &index_key,
+					   &persistent_ref);
 	up_write(&ns->keyring_sem);
-	if (!IS_ERR(persistent_ref))
-		goto found;
-
-	return PTR_ERR(persistent_ref);
+	if (ret < 0)
+		return ret;
+	created = ret == 0;
 
 found:
+	persistent = key_ref_to_ptr(persistent_ref);
 	ret = key_task_permission(persistent_ref, current_cred(), KEY_NEED_LINK);
-	if (ret == 0) {
-		persistent = key_ref_to_ptr(persistent_ref);
+	if (ret == 0)
 		ret = key_link(key_ref_to_ptr(dest_ref), persistent);
-		if (ret == 0) {
-			key_set_timeout(persistent, persistent_keyring_expiry);
-			ret = persistent->serial;
-		}
-	}
+
+	if (ret == 0 || created)
+		key_set_timeout(persistent, persistent_keyring_expiry);
+
+	if (ret == 0)
+		ret = persistent->serial;
 
 	key_ref_put(persistent_ref);
 	return ret;