[PATCH 6/7] keys: Provide a key_try_get() function and use it

David Howells
2024-08-21T12:36:44Z

Add a key_try_get() function to try to get a ref on a key and switch code
that's manipulating the key refcount directly to use it. This will allow a
tracepoint to be emplaced there later.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jarkko Sakkinen <jarkko@kernel.org>
cc: keyrings@vger.kernel.org
cc: linux-security-module@vger.kernel.org
---
include/linux/key.h | 1 +
security/keys/key.c | 16 +++++++++++++++-
security/keys/keyring.c | 2 +-
3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/linux/key.h b/include/linux/key.h
index 80d736813b89..4e5baf3e7286 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -300,6 +300,7 @@ extern struct key *key_alloc(struct key_type *type,
extern void key_revoke(struct key *key);
extern void key_invalidate(struct key *key);
struct key *key_get(struct key *key);
+struct key *key_try_get(struct key *key);
extern void key_put(struct key *key);
extern bool key_put_tag(struct key_tag *tag);
extern void key_remove_domain(struct key_tag *domain_tag);
diff --git a/security/keys/key.c b/security/keys/key.c
index 14c7ee77ea15..59cffb6f9b94 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -649,6 +649,20 @@ struct key *key_get(struct key *key)
}
EXPORT_SYMBOL(key_get);

+/**
+ * key_try_get - Get a ref on a key if its refcount is not non-zero.
+ * @key: The key to get a reference on.
+ *
+ * Get a reference on a key unless it has no references and return true if
+ * successful. @key must not be NULL.
+ */
+struct key *key_try_get(struct key *key)
+{
+ if (!refcount_inc_not_zero(&key->usage))
+ return NULL;
+ return key;
+}
+
/**
* key_put - Discard a reference to a key.
* @key: The key to discard a reference from.
@@ -709,7 +723,7 @@ struct key *key_lookup(key_serial_t id)
/* A key is allowed to be looked up only if someone still owns a
* reference to it - otherwise it's awaiting the gc.
*/
- if (!refcount_inc_not_zero(&key->usage))
+ if (!key_try_get(key))
goto not_found;

error:
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index e77d927f1d4d..a09a4c2b1bcb 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -1174,7 +1174,7 @@ struct key *find_keyring_by_name(const char *name, bool uid_keyring)
/* we've got a match but we might end up racing with
* key_cleanup() if the keyring is currently 'dead'
* (ie. it has a zero usage count) */
- if (!refcount_inc_not_zero(&keyring->usage))
+ if (!key_try_get(keyring))
continue;
keyring->last_used_at = ktime_get_real_seconds();
goto out;