KEYS: Add a 'trusted' flag and a 'trusted only' flag

Add KEY_FLAG_TRUSTED to indicate that a key either comes from a trusted source
or had a cryptographic signature chain that led back to a trusted key the
kernel already possessed.

Add KEY_FLAGS_TRUSTED_ONLY to indicate that a keyring will only accept links to
keys marked with KEY_FLAGS_TRUSTED.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

5 files changed, 19 insertions, 1 deletions

diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index f58737bcb050..a74c3a84dfdd 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -45,6 +45,7 @@ struct key_preparsed_payload {
         const void      *data;          /* Raw data */
         size_t          datalen;        /* Raw datalen */
         size_t          quotalen;       /* Quota length for proposed payload */
+        bool            trusted;        /* True if key is trusted */
 };
 
 typedef int (*request_key_actor_t)(struct key_construction *key,
diff --git a/include/linux/key.h b/include/linux/key.h
index 010dbb618aca..80d677483e31 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -168,6 +168,8 @@ struct key {
 #define KEY_FLAG_NEGATIVE       5       /* set if key is negative */
 #define KEY_FLAG_ROOT_CAN_CLEAR 6       /* set if key can be cleared by root without permission */
 #define KEY_FLAG_INVALIDATED    7       /* set if key has been invalidated */
+#define KEY_FLAG_TRUSTED        8       /* set if key is trusted */
+#define KEY_FLAG_TRUSTED_ONLY   9       /* set if keyring only accepts links to trusted keys */
 
         /* the key type and key description string
          * - the desc is used to match a key against search criteria
@@ -218,6 +220,7 @@ extern struct key *key_alloc(struct key_type *type,
 #define KEY_ALLOC_IN_QUOTA      0x0000  /* add to quota, reject if would overrun */
 #define KEY_ALLOC_QUOTA_OVERRUN 0x0001  /* add to quota, permit even if overrun */
 #define KEY_ALLOC_NOT_IN_QUOTA  0x0002  /* not in quota */
+#define KEY_ALLOC_TRUSTED       0x0004  /* Key should be flagged as trusted */
 
 extern void key_revoke(struct key *key);
 extern void key_invalidate(struct key *key);
diff --git a/kernel/system_keyring.c b/kernel/system_keyring.c
index 51c35141a13a..5296721eca5b 100644
--- a/kernel/system_keyring.c
+++ b/kernel/system_keyring.c
@@ -40,6 +40,7 @@ static __init int system_trusted_keyring_init(void)
         if (IS_ERR(system_trusted_keyring))
                 panic("Can't allocate system trusted keyring\n");
 
+        set_bit(KEY_FLAG_TRUSTED_ONLY, &system_trusted_keyring->flags);
         return 0;
 }
 
@@ -82,7 +83,8 @@ static __init int load_system_certificate_list(void)
                                            plen,
                                            (KEY_POS_ALL & ~KEY_POS_SETATTR) |
                                            KEY_USR_VIEW,
-                                           KEY_ALLOC_NOT_IN_QUOTA);
+                                           KEY_ALLOC_NOT_IN_QUOTA |
+                                           KEY_ALLOC_TRUSTED);
                 if (IS_ERR(key)) {
                         pr_err("Problem loading in-kernel X.509 certificate (%ld)\n",
                                PTR_ERR(key));
diff --git a/security/keys/key.c b/security/keys/key.c
index a819b5c7d4ec..d331ea9ef380 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -300,6 +300,8 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 
         if (!(flags & KEY_ALLOC_NOT_IN_QUOTA))
                 key->flags |= 1 << KEY_FLAG_IN_QUOTA;
+        if (flags & KEY_ALLOC_TRUSTED)
+                key->flags |= 1 << KEY_FLAG_TRUSTED;
 
         memset(&key->type_data, 0, sizeof(key->type_data));
 
@@ -813,6 +815,7 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
         prep.data = payload;
         prep.datalen = plen;
         prep.quotalen = index_key.type->def_datalen;
+        prep.trusted = flags & KEY_ALLOC_TRUSTED;
         if (index_key.type->preparse) {
                 ret = index_key.type->preparse(&prep);
                 if (ret < 0) {
@@ -827,6 +830,11 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
         }
         index_key.desc_len = strlen(index_key.description);
 
+        key_ref = ERR_PTR(-EPERM);
+        if (!prep.trusted && test_bit(KEY_FLAG_TRUSTED_ONLY, &keyring->flags))
+                goto error_free_prep;
+        flags |= prep.trusted ? KEY_ALLOC_TRUSTED : 0;
+
         ret = __key_link_begin(keyring, &index_key, &edit);
         if (ret < 0) {
                 key_ref = ERR_PTR(ret);
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index f7cdea22214f..9b6f6e09b50c 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -1183,6 +1183,10 @@ int key_link(struct key *keyring, struct key *key)
         key_check(keyring);
         key_check(key);
 
+        if (test_bit(KEY_FLAG_TRUSTED_ONLY, &keyring->flags) &&
+            !test_bit(KEY_FLAG_TRUSTED, &key->flags))
+                return -EPERM;
+
         ret = __key_link_begin(keyring, &key->index_key, &edit);
         if (ret == 0) {
                 kdebug("begun {%d,%d}", keyring->serial, atomic_read(&keyring->usage));