From dd3ea3fcba7c75493760cdbccd35f029597e8d5e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=EC=84=B1=EB=B3=91=EC=B0=AC?= Date: Wed, 30 Sep 2026 13:18:01 +0900 Subject: [PATCH] KEYS: Fix add_key() race with keyring restriction MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit __key_create_or_update() snapshots keyring->restrict_link before taking the destination keyring's semaphore. keyring_restrict() installs a restriction while holding that semaphore. This allows a writer to observe no restriction, wait for the keyring owner to install a reject-all restriction and return successfully, and then link a key using the stale NULL snapshot. The writer only needs write permission on the destination keyring. Move the restrict_link read after __key_link_lock() and __key_link_begin(). The read and the subsequent restriction check are then serialized with restriction installation by keyring->sem. The race was reproduced on v7.2.8 in 19 executions where restriction installation returned before the link completed. All 19 linked the key despite the reject-all restriction. With this change, 312 executions reached the same ordering and every add_key() call failed with -EPERM. The issue was found by manual concurrency analysis assisted by AI-based analysis and independently verified with a QEMU reproducer and kernel instrumentation. Fixes: 5ac7eace2d00 ("KEYS: Add a facility to restrict new links into a keyring") Cc: stable@vger.kernel.org Signed-off-by: 성병찬 Reviewed-by: Jarkko Sakkinen Link: https://lore.kernel.org/r/20260930041802.6114-1-tjdqudcks0424@naver.com Signed-off-by: Jarkko Sakkinen --- security/keys/key.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/security/keys/key.c b/security/keys/key.c index b34a64d81d47..a438c4508595 100644 --- a/security/keys/key.c +++ b/security/keys/key.c @@ -840,9 +840,6 @@ static key_ref_t __key_create_or_update(key_ref_t keyring_ref, key_check(keyring); - if (!(flags & KEY_ALLOC_BYPASS_RESTRICTION)) - restrict_link = keyring->restrict_link; - key_ref = ERR_PTR(-ENOTDIR); if (keyring->type != &key_type_keyring) goto error_put_type; @@ -880,6 +877,9 @@ static key_ref_t __key_create_or_update(key_ref_t keyring_ref, goto error_link_end; } + if (!(flags & KEY_ALLOC_BYPASS_RESTRICTION)) + restrict_link = keyring->restrict_link; + if (restrict_link && restrict_link->check) { ret = restrict_link->check(keyring, index_key.type, &prep.payload, restrict_link->key);