[PATCH] Keys: Add possessor permissions to keys [try #3]

The attached patch adds extra permission grants to keys for the possessor of a
key in addition to the owner, group and other permissions bits. This makes
SUID binaries easier to support without going as far as labelling keys and key
targets using the LSM facilities.

This patch adds a second "pointer type" to key structures (struct key_ref *)
that can have the bottom bit of the address set to indicate the possession of
a key. This is propagated through searches from the keyring to the discovered
key. It has been made a separate type so that the compiler can spot attempts
to dereference a potentially incorrect pointer.

The "possession" attribute can't be attached to a key structure directly as
it's not an intrinsic property of a key.

Pointers to keys have been replaced with struct key_ref *'s wherever
possession information needs to be passed through.

This does assume that the bottom bit of the pointer will always be zero on
return from kmem_cache_alloc().

The key reference type has been made into a typedef so that at least it can be
located in the sources, even though it's basically a pointer to an undefined
type. I've also renamed the accessor functions to be more useful, and all
reference variables should now end in "_ref".

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 50 insertions, 36 deletions

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 9c208c756df8..0639396dd441 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -309,7 +309,7 @@ struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
         int ret;
 
         keyring = key_alloc(&key_type_keyring, description,
-                            uid, gid, KEY_USR_ALL, not_in_quota);
+                            uid, gid, KEY_POS_ALL | KEY_USR_ALL, not_in_quota);
 
         if (!IS_ERR(keyring)) {
                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
@@ -333,12 +333,13 @@ struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
  * - we rely on RCU to prevent the keyring lists from disappearing on us
  * - we return -EAGAIN if we didn't find any matching key
  * - we return -ENOKEY if we only found negative matching keys
+ * - we propagate the possession attribute from the keyring ref to the key ref
  */
-struct key *keyring_search_aux(struct key *keyring,
-                               struct task_struct *context,
-                               struct key_type *type,
-                               const void *description,
-                               key_match_func_t match)
+key_ref_t keyring_search_aux(key_ref_t keyring_ref,
+                             struct task_struct *context,
+                             struct key_type *type,
+                             const void *description,
+                             key_match_func_t match)
 {
         struct {
                 struct keyring_list *keylist;
@@ -347,29 +348,33 @@ struct key *keyring_search_aux(struct key *keyring,
 
         struct keyring_list *keylist;
         struct timespec now;
-        struct key *key;
+        unsigned long possessed;
+        struct key *keyring, *key;
+        key_ref_t key_ref;
         long err;
         int sp, kix;
 
+        keyring = key_ref_to_ptr(keyring_ref);
+        possessed = is_key_possessed(keyring_ref);
         key_check(keyring);
 
-        rcu_read_lock();
-
         /* top keyring must have search permission to begin the search */
-        key = ERR_PTR(-EACCES);
-        if (!key_task_permission(keyring, context, KEY_SEARCH))
+        key_ref = ERR_PTR(-EACCES);
+        if (!key_task_permission(keyring_ref, context, KEY_SEARCH))
                 goto error;
 
-        key = ERR_PTR(-ENOTDIR);
+        key_ref = ERR_PTR(-ENOTDIR);
         if (keyring->type != &key_type_keyring)
                 goto error;
 
+        rcu_read_lock();
+
         now = current_kernel_time();
         err = -EAGAIN;
         sp = 0;
 
         /* start processing a new keyring */
- descend:
+descend:
         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
                 goto not_this_keyring;
 
@@ -397,7 +402,8 @@ struct key *keyring_search_aux(struct key *keyring,
                         continue;
 
                 /* key must have search permissions */
-                if (!key_task_permission(key, context, KEY_SEARCH))
+                if (!key_task_permission(make_key_ref(key, possessed),
+                                         context, KEY_SEARCH))
                         continue;
 
                 /* we set a different error code if we find a negative key */
@@ -411,7 +417,7 @@ struct key *keyring_search_aux(struct key *keyring,
 
         /* search through the keyrings nested in this one */
         kix = 0;
- ascend:
+ascend:
         for (; kix < keylist->nkeys; kix++) {
                 key = keylist->keys[kix];
                 if (key->type != &key_type_keyring)
@@ -423,7 +429,8 @@ struct key *keyring_search_aux(struct key *keyring,
                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
                         continue;
 
-                if (!key_task_permission(key, context, KEY_SEARCH))
+                if (!key_task_permission(make_key_ref(key, possessed),
+                                         context, KEY_SEARCH))
                         continue;
 
                 /* stack the current position */
@@ -438,7 +445,7 @@ struct key *keyring_search_aux(struct key *keyring,
 
         /* the keyring we're looking at was disqualified or didn't contain a
          * matching key */
- not_this_keyring:
+not_this_keyring:
         if (sp > 0) {
                 /* resume the processing of a keyring higher up in the tree */
                 sp--;
@@ -447,16 +454,18 @@ struct key *keyring_search_aux(struct key *keyring,
                 goto ascend;
         }
 
-        key = ERR_PTR(err);
-        goto error;
+        key_ref = ERR_PTR(err);
+        goto error_2;
 
         /* we found a viable match */
- found:
+found:
         atomic_inc(&key->usage);
         key_check(key);
- error:
+        key_ref = make_key_ref(key, possessed);
+error_2:
         rcu_read_unlock();
-        return key;
+error:
+        return key_ref;
 
 } /* end keyring_search_aux() */
 
@@ -469,9 +478,9 @@ struct key *keyring_search_aux(struct key *keyring,
  * - we return -EAGAIN if we didn't find any matching key
  * - we return -ENOKEY if we only found negative matching keys
  */
-struct key *keyring_search(struct key *keyring,
-                           struct key_type *type,
-                           const char *description)
+key_ref_t keyring_search(key_ref_t keyring,
+                         struct key_type *type,
+                         const char *description)
 {
         if (!type->match)
                 return ERR_PTR(-ENOKEY);
@@ -488,15 +497,19 @@ EXPORT_SYMBOL(keyring_search);
  * search the given keyring only (no recursion)
  * - keyring must be locked by caller
  */
-struct key *__keyring_search_one(struct key *keyring,
-                                 const struct key_type *ktype,
-                                 const char *description,
-                                 key_perm_t perm)
+key_ref_t __keyring_search_one(key_ref_t keyring_ref,
+                               const struct key_type *ktype,
+                               const char *description,
+                               key_perm_t perm)
 {
         struct keyring_list *klist;
-        struct key *key;
+        unsigned long possessed;
+        struct key *keyring, *key;
         int loop;
 
+        keyring = key_ref_to_ptr(keyring_ref);
+        possessed = is_key_possessed(keyring_ref);
+
         rcu_read_lock();
 
         klist = rcu_dereference(keyring->payload.subscriptions);
@@ -507,21 +520,21 @@ struct key *__keyring_search_one(struct key *keyring,
                         if (key->type == ktype &&
                             (!key->type->match ||
                              key->type->match(key, description)) &&
-                            key_permission(key, perm) &&
+                            key_permission(make_key_ref(key, possessed),
+                                           perm) &&
                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
                             )
                                 goto found;
                 }
         }
 
-        key = ERR_PTR(-ENOKEY);
-        goto error;
+        rcu_read_unlock();
+        return ERR_PTR(-ENOKEY);
 
  found:
         atomic_inc(&key->usage);
- error:
         rcu_read_unlock();
-        return key;
+        return make_key_ref(key, possessed);
 
 } /* end __keyring_search_one() */
 
@@ -603,7 +616,8 @@ struct key *find_keyring_by_name(const char *name, key_serial_t bound)
                         if (strcmp(keyring->description, name) != 0)
                                 continue;
 
-                        if (!key_permission(keyring, KEY_SEARCH))
+                        if (!key_permission(make_key_ref(keyring, 0),
+                                            KEY_SEARCH))
                                 continue;
 
                         /* found a potential candidate, but we still need to