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Thu, 08 Oct 2026 22:12:06 -0700 (PDT) From: Cen Zhang To: dhowells@redhat.com, jarkko@kernel.org, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, sergeh@kernel.org Cc: keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com, zzzccc427@gmail.com Subject: [PATCH v2] keys: Avoid the owner account dereference in named keyring lookup Date: Fri, 9 Oct 2026 13:11:59 +0800 Message-Id: X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Named keyring lookup must keep the storage containing the owner UID alive through the namespace mapping check. find_keyring_by_name() reads keyring->user->uid under keyring_name_lock, but that lock protects the keyring's name entry and allocation, not its separate key_user. A named session-keyring join can overlap a privileged KEYCTL_CHOWN on another CPU. If the keyring holds the last reference to its old dynamic key_user and the ownership transfer succeeds, the following ordering is possible: Named join Chown find_keyring_by_name() keyctl_chown_key() read_lock(keyring_name_lock) down_write(key->sem) load old keyring->user replace key->user and key->uid up_write(key->sem) key_put(key) key_user_put(old user): free read old user->uid read_unlock(keyring_name_lock) Chown neither takes keyring_name_lock nor key_session_mutex, so it can free the old account between the pointer load and the UID read. The lookup then reads freed memory even though the keyring itself is alive. Use keyring->uid for the mapping check. key_alloc() initializes this inline owner UID and keyctl_chown_key() updates it on chown. The existing name lock keeps its containing keyring allocated throughout the check, so lookup no longer depends on the account's lifetime. This also matches the owner UID used by the permission check. KASAN report as below: BUG: KASAN: slab-use-after-free in find_keyring_by_name+0x577/0x5d0 Read of size 4 at addr ffff8881128ae2ec by task keycase/500 Fixes: 2ea190d0a006 ("keys: skip keys from another user namespace") Assisted-by: LLM Signed-off-by: Cen Zhang --- Changes in v2: - Trim the KASAN report to its two-line fault summary. Link to v1: https://lore.kernel.org/r/pm-key-management-objects-candidate-0002-v2-dd6c20a1d92928b33ab7@gmail.com diff --git a/security/keys/keyring.c b/security/keys/keyring.c index 15bf4af8f28218ec3f12c97630d1c76939af7eca..46f774be72967a9bd16b0ddfdf323eda36edeff4 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, keyring->uid)) continue; if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))