CVE-2026-99040KEYS: Fix add_key() race with keyring restriction

Official description

In the Linux kernel, the following vulnerability has been resolved: KEYS: Fix add_key() race with keyring restriction __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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/24806fc9bca28fa1433bf938d1424dcb45d80e50
• https://git.kernel.org/stable/c/9a5c2700336878465a630804a2d21864f22eca9c
• https://git.kernel.org/stable/c/b3e404550dc2b7f3d4bb64b1da8005a1fa9a798d
• https://git.kernel.org/stable/c/305f1828b871dd46bf41addeb6f11d2c162dcb25
• https://git.kernel.org/stable/c/f99399b48e3edd6851fac34cd329bab9f1f33baf
• https://git.kernel.org/stable/c/11516a0c402a6c1fa52254aa70d8d65fb921e59e
• https://git.kernel.org/stable/c/da0b595d8e6e2dd798f6e34e09dc51a13b888514
• https://git.kernel.org/stable/c/dd3ea3fcba7c75493760cdbccd35f029597e8d5e