[PATCH v2] KEYS: do not let an unmatched key decide the search result

["Guixiong Wei" <weiguixiong@bytedance.com>]

With the dns_resolver key type available, put a key named "foo" in a
fresh session keyring, revoke it, and search for "bar":

  keyctl new_session >/dev/null
  A=$(printf '127.0.0.1\0' | keyctl padd dns_resolver foo @s)
  keyctl revoke "$A"
  keyctl search @s dns_resolver bar

Results:

  keyctl_search: Key has been revoked

The search returns -EKEYREVOKED even though there is no key named "bar".
It should return -ENOKEY.

A dns_resolver search walks the keys in the keyring and uses
dns_resolver_cmp() to compare their descriptions with the requested
name. When keyring_search_iterator() sees the revoked "foo" key, it
records -EKEYREVOKED in ctx->result and skips the key before comparing
its description. The search continues, but without a match it returns
the error recorded for "foo".

Call the match callback before checking for invalidated, revoked or
expired keys. A nonmatching key then leaves ctx->result alone.

Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
Reported-by: Jarkko Sakkinen <jarkko@kernel.org>
Closes: https://lore.kernel.org/lkml/avDG8G-Jl1YsmfCs@kernel.org/
Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com>
---

Changes in v2:
- Explain the wrong errno using Jarkko's original reproducer and output.
- Clarify that the search continues after skipping the revoked key.
- Add Reported-by and Closes tags. Keep the code diff unchanged.

v1: https://lore.kernel.org/lkml/20261108131413.12012-2-weiguixiong@bytedance.com/

 security/keys/keyring.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 7143f3079d200..39645b8f9b30c 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -598,6 +598,12 @@ static int keyring_search_iterator(const void *object, void *iterator_data)
 		return 0;
 	}
 
+	/* A key the caller did not ask for must not decide the result. */
+	if (!ctx->match_data.cmp(key, &ctx->match_data)) {
+		kleave(" = 0 [!match]");
+		return 0;
+	}
+
 	/* skip invalidated, revoked and expired keys */
 	if (ctx->flags & KEYRING_SEARCH_DO_STATE_CHECK) {
 		time64_t expiry = READ_ONCE(key->expiry);
@@ -617,12 +623,6 @@ static int keyring_search_iterator(const void *object, void *iterator_data)
 		}
 	}
 
-	/* keys that don't match */
-	if (!ctx->match_data.cmp(key, &ctx->match_data)) {
-		kleave(" = 0 [!match]");
-		return 0;
-	}
-
 	/* key must have search permissions */
 	if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM) &&
 	    key_task_permission(make_key_ref(key, ctx->possessed),
-- 
2.55.0