[PATCH v3] asymmetric_keys: reject trust keys without IDs

[Weiming Shi]

The PKCS#8 parser deliberately leaves the asym_key_ids payload slot
empty. key_or_keyring_common() unconditionally dereferences that slot
when a PKCS#8 key is supplied to a key_or_keyring restriction. Both the
plain and :chain forms reach this branch, allowing an unprivileged caller
to trigger a NULL pointer dereference through KEYCTL_RESTRICT_KEYRING
followed by add_key().

 Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000
 KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
 RIP: 0010:key_or_keyring_common (crypto/asymmetric_keys/restrict.c:205 crypto/asymmetric_keys/restrict.c:279)
 Call Trace:
  <TASK>
  __key_create_or_update (security/keys/key.c:884)
  key_create_or_update (security/keys/key.c:1021)
  __do_sys_add_key (security/keys/keyctl.c:134)
  do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
  </TASK>
 Kernel panic - not syncing: Fatal exception

Reject an asymmetric restriction key without key IDs. A PKCS#8 private
key cannot identify the signer of a candidate certificate and is not a
valid trust anchor.

Fixes: 3c58b2362ba8 ("KEYS: Implement PKCS#8 RSA Private Key parser [ver #2]")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Xiang Mei <xmei5@xxxxxxx>
Link: https://lore.kernel.org/r/20260429181629.110802-2-bestswngs@xxxxxxxxx
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
---
Changes in v3:
- Drop the unnecessary find_asymmetric_key() check.
- Reject a trust key without IDs instead of continuing the chain lookup.
- Use the PKCS#8 parser commit as the Fixes target.

 crypto/asymmetric_keys/restrict.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
index 86292965f..0e4783ff7 100644
--- a/crypto/asymmetric_keys/restrict.c
+++ b/crypto/asymmetric_keys/restrict.c
@@ -243,10 +243,14 @@ static int key_or_keyring_common(struct key *dest_keyring,
 			if (IS_ERR(key))
 				key = NULL;
 		} else if (trusted->type == &key_type_asymmetric) {
+			const struct asymmetric_key_ids *kids;
 			const struct asymmetric_key_id **signer_ids;
 
-			signer_ids = (const struct asymmetric_key_id **)
-				asymmetric_key_ids(trusted)->id;
+			kids = asymmetric_key_ids(trusted);
+			if (!kids)
+				return -ENOKEY;
+
+			signer_ids = (const struct asymmetric_key_id **)kids->id;
 
 			/*
 			 * The auth_ids come from the candidate key (the
-- 
2.55.0