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Subject[PATCH 06/11] keys: Namespace keyring names
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Keyring names are held in a single global list that any process can pick
from by means of keyctl_join_session_keyring (provided the keyring grants
Search permission). This isn't very container friendly, however.

Make the following changes:

(1) Make default session, process and thread keyring names begin with a
'.' instead of '_'.

(2) Keyrings whose names begin with a '.' aren't added to the list. Such
keyrings are system specials.

(3) Replace the global list with per-user_namespace lists. A keyring adds
its name to the list for the user_namespace that it is currently in.

(4) When a user_namespace is deleted, it just removes itself from the
keyring name list.

The global keyring_name_lock is retained for accessing the name lists.
This allows (4) to work.

This can be tested by:

# keyctl newring foo @s
995906392
# unshare -U
$ keyctl show
...
995906392 --alswrv 65534 65534 \_ keyring: foo
...
$ keyctl session foo
Joined session keyring: 935622349

As can be seen, a new session keyring was created.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Eric W. Biederman <ebiederm@xmission.com>
---

include/linux/key.h | 2 +
include/linux/user_namespace.h | 5 ++
kernel/user.c | 3 +
kernel/user_namespace.c | 7 ++-
security/keys/keyring.c | 99 +++++++++++++++++-----------------------
5 files changed, 57 insertions(+), 59 deletions(-)

diff --git a/include/linux/key.h b/include/linux/key.h
index bdd179169508..52334cc7c18d 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -353,6 +353,7 @@ extern void key_set_timeout(struct key *, unsigned);

extern key_ref_t lookup_user_key(key_serial_t id, unsigned long flags,
key_perm_t perm);
+extern void key_free_user_ns(struct user_namespace *);

/*
* The permissions required on a key that we're looking up.
@@ -426,6 +427,7 @@ extern void key_init(void);
#define key_fsuid_changed(t) do { } while(0)
#define key_fsgid_changed(t) do { } while(0)
#define key_init() do { } while(0)
+#define key_free_user_ns(ns) do { } while(0)

#endif /* CONFIG_KEYS */
#endif /* __KERNEL__ */
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index d6b74b91096b..90457015fa3f 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -64,6 +64,11 @@ struct user_namespace {
struct ns_common ns;
unsigned long flags;

+#ifdef CONFIG_KEYS
+ /* List of joinable keyrings in this namespace */
+ struct list_head keyring_name_list;
+#endif
+
/* Register of per-UID persistent keyrings for this namespace */
#ifdef CONFIG_PERSISTENT_KEYRINGS
struct key *persistent_keyring_register;
diff --git a/kernel/user.c b/kernel/user.c
index 0df9b1640b2a..6a6ccb99f31a 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -62,6 +62,9 @@ struct user_namespace init_user_ns = {
.ns.ops = &userns_operations,
#endif
.flags = USERNS_INIT_FLAGS,
+#ifdef CONFIG_KEYS
+ .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
+#endif
#ifdef CONFIG_PERSISTENT_KEYRINGS
.persistent_keyring_register_sem =
__RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 923414a246e9..bda6e890ad88 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -133,6 +133,9 @@ int create_user_ns(struct cred *new)
ns->flags = parent_ns->flags;
mutex_unlock(&userns_state_mutex);

+#ifdef CONFIG_KEYS
+ INIT_LIST_HEAD(&ns->keyring_name_list);
+#endif
#ifdef CONFIG_PERSISTENT_KEYRINGS
init_rwsem(&ns->persistent_keyring_register_sem);
#endif
@@ -196,9 +199,7 @@ static void free_user_ns(struct work_struct *work)
kfree(ns->projid_map.reverse);
}
retire_userns_sysctls(ns);
-#ifdef CONFIG_PERSISTENT_KEYRINGS
- key_put(ns->persistent_keyring_register);
-#endif
+ key_free_user_ns(ns);
ns_free_inum(&ns->ns);
kmem_cache_free(user_ns_cachep, ns);
dec_user_namespaces(ucounts);
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 29a6e3255157..48eda80afe89 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -16,6 +16,7 @@
#include <linux/security.h>
#include <linux/seq_file.h>
#include <linux/err.h>
+#include <linux/user_namespace.h>
#include <keys/keyring-type.h>
#include <keys/user-type.h>
#include <linux/assoc_array_priv.h>
@@ -28,11 +29,6 @@
*/
#define KEYRING_SEARCH_MAX_DEPTH 6

-/*
- * We keep all named keyrings in a hash to speed looking them up.
- */
-#define KEYRING_NAME_HASH_SIZE (1 << 5)
-
/*
* We mark pointers we pass to the associative array with bit 1 set if
* they're keyrings and clear otherwise.
@@ -55,17 +51,20 @@ static inline void *keyring_key_to_ptr(struct key *key)
return key;
}

-static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
static DEFINE_RWLOCK(keyring_name_lock);

-static inline unsigned keyring_hash(const char *desc)
+/*
+ * Clean up the bits of user_namespace that belong to us.
+ */
+void key_free_user_ns(struct user_namespace *ns)
{
- unsigned bucket = 0;
-
- for (; *desc; desc++)
- bucket += (unsigned char)*desc;
+ write_lock(&keyring_name_lock);
+ list_del_init(&ns->keyring_name_list);
+ write_unlock(&keyring_name_lock);

- return bucket & (KEYRING_NAME_HASH_SIZE - 1);
+#ifdef CONFIG_PERSISTENT_KEYRINGS
+ key_put(ns->persistent_keyring_register);
+#endif
}

/*
@@ -104,23 +103,17 @@ static DECLARE_RWSEM(keyring_serialise_link_sem);

/*
* Publish the name of a keyring so that it can be found by name (if it has
- * one).
+ * one and it doesn't begin with a dot).
*/
static void keyring_publish_name(struct key *keyring)
{
- int bucket;
-
- if (keyring->description) {
- bucket = keyring_hash(keyring->description);
+ struct user_namespace *ns = current_user_ns();

+ if (keyring->description &&
+ keyring->description[0] &&
+ keyring->description[0] != '.') {
write_lock(&keyring_name_lock);
-
- if (!keyring_name_hash[bucket].next)
- INIT_LIST_HEAD(&keyring_name_hash[bucket]);
-
- list_add_tail(&keyring->name_link,
- &keyring_name_hash[bucket]);
-
+ list_add_tail(&keyring->name_link, &ns->keyring_name_list);
write_unlock(&keyring_name_lock);
}
}
@@ -1091,50 +1084,44 @@ key_ref_t find_key_to_update(key_ref_t keyring_ref,
*/
struct key *find_keyring_by_name(const char *name, bool uid_keyring)
{
+ struct user_namespace *ns = current_user_ns();
struct key *keyring;
- int bucket;

if (!name)
return ERR_PTR(-EINVAL);

- bucket = keyring_hash(name);
-
read_lock(&keyring_name_lock);

- if (keyring_name_hash[bucket].next) {
- /* search this hash bucket for a keyring with a matching name
- * that's readable and that hasn't been revoked */
- list_for_each_entry(keyring,
- &keyring_name_hash[bucket],
- name_link
- ) {
- if (!kuid_has_mapping(current_user_ns(), keyring->user->uid))
- continue;
-
- if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
- continue;
+ /* Search this hash bucket for a keyring with a matching name that
+ * grants Search permission and that hasn't been revoked
+ */
+ list_for_each_entry(keyring, &ns->keyring_name_list, name_link) {
+ if (!kuid_has_mapping(ns, keyring->user->uid))
+ continue;

- if (strcmp(keyring->description, name) != 0)
- continue;
+ if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
+ continue;

- if (uid_keyring) {
- if (!test_bit(KEY_FLAG_UID_KEYRING,
- &keyring->flags))
- continue;
- } else {
- if (key_permission(make_key_ref(keyring, 0),
- KEY_NEED_SEARCH) < 0)
- continue;
- }
+ if (strcmp(keyring->description, name) != 0)
+ continue;

- /* 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 (uid_keyring) {
+ if (!test_bit(KEY_FLAG_UID_KEYRING,
+ &keyring->flags))
+ continue;
+ } else {
+ if (key_permission(make_key_ref(keyring, 0),
+ KEY_NEED_SEARCH) < 0)
continue;
- keyring->last_used_at = ktime_get_real_seconds();
- goto out;
}
+
+ /* 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))
+ continue;
+ keyring->last_used_at = ktime_get_real_seconds();
+ goto out;
}

keyring = ERR_PTR(-ENOKEY);
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