keys: Protect the read method check against type removal

Overview

In the Linux kernel, the following vulnerability has been resolved:

keys: Protect the read method check against type removal

keyctl_read_key() checks key->type->read without holding key->sem. A reference keeps the key alive, but does not pin the module containing its type. A surviving RxRPC key can therefore be read while AF_RXRPC is being unloaded:

KEYCTL_READ task Module unload and key GC

---

lookup_user_key() permission / possession checks load key->type af_rxrpc_exit() unregister_key_type() GC: down_write(key->sem) GC: retype to key_type_dead GC: up_write(key->sem) unregister_key_type() returns free_module() read saved type's read member

The final access can read freed module storage. The read invocation in __keyctl_read_key() is already protected by key->sem, but the earlier method check is outside that critical section.

Move the method check into __keyctl_read_key(), after key_validate() and under its existing read hold on key->sem. The check and invocation then use the same protected type for length queries and every read retry. The GC cannot retype the key until the semaphore is released, and type unregistration waits for that GC pass before the module can be freed.

Return -EOPNOTSUPP when validation succeeds and the type has no read method. A temporary buffer may now be allocated before this result; allocation and copying to userspace remain outside the semaphore.

Affected

• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < e5f830ae6611cddbfc504c43f14155f60b63206a
• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < ff11cfed85cbfdd7fe1185ebd18d2c7a8353ad8d
• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < 1486caee47b4909f52835a957c3293e970113e44
• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < ff44f1b303aa76a818d898e85c56ed4852c031e2
• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < 6a36e2a1a017c51f8a8ad2a094566bad97c46a9b
• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < 3edc064069d07e7d37359fcb4d03d3bab15ee3ab
• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < cf1af7df80e38bf58bd74c2cccce32fcbd1a596a
• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < e2a2deda08d91644f5e30c17d267b1cdc5f124b2
• Linux >= d3ec10aa95819bff18a0d936b18884c7816d0914 < 925c84e3cc21caf09de92d9bcafab0147790debf
• Linux 7fa67aa30509ad0da72ac0f757aa76e53c0ea3de
• Linux 18779eac17b5df9dff57138d07631573553a41d4
• Linux f1afcf9488fc45765e20e2047d3b776981900e0b
• Linux 212d3adb1af4e34acb158d6c6def370016a1011d
• Linux >= 4.14.177 < 4.15
• Linux >= 4.19.118 < 4.20
• Linux >= 5.4.35 < 5.5
• Linux >= 5.6.7 < 5.7
• Linux 5.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.