[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, 19 insertions, 9 deletions

diff --git a/include/linux/key-ui.h b/include/linux/key-ui.h
index cc326174a808..918c34a8347e 100644
--- a/include/linux/key-ui.h
+++ b/include/linux/key-ui.h
@@ -42,11 +42,14 @@ struct keyring_list {
 /*
  * check to see whether permission is granted to use a key in the desired way
  */
-static inline int key_permission(const struct key *key, key_perm_t perm)
+static inline int key_permission(const key_ref_t key_ref, key_perm_t perm)
 {
+	struct key *key = key_ref_to_ptr(key_ref);
 	key_perm_t kperm;
 
-	if (key->uid == current->fsuid)
+	if (is_key_possessed(key_ref))
+		kperm = key->perm >> 24;
+	else if (key->uid == current->fsuid)
 		kperm = key->perm >> 16;
 	else if (key->gid != -1 &&
 		 key->perm & KEY_GRP_ALL &&
@@ -65,11 +68,14 @@ static inline int key_permission(const struct key *key, key_perm_t perm)
  * check to see whether permission is granted to use a key in at least one of
  * the desired ways
  */
-static inline int key_any_permission(const struct key *key, key_perm_t perm)
+static inline int key_any_permission(const key_ref_t key_ref, key_perm_t perm)
 {
+	struct key *key = key_ref_to_ptr(key_ref);
 	key_perm_t kperm;
 
-	if (key->uid == current->fsuid)
+	if (is_key_possessed(key_ref))
+		kperm = key->perm >> 24;
+	else if (key->uid == current->fsuid)
 		kperm = key->perm >> 16;
 	else if (key->gid != -1 &&
 		 key->perm & KEY_GRP_ALL &&
@@ -94,13 +100,17 @@ static inline int key_task_groups_search(struct task_struct *tsk, gid_t gid)
 	return ret;
 }
 
-static inline int key_task_permission(const struct key *key,
+static inline int key_task_permission(const key_ref_t key_ref,
 				      struct task_struct *context,
 				      key_perm_t perm)
 {
+	struct key *key = key_ref_to_ptr(key_ref);
 	key_perm_t kperm;
 
-	if (key->uid == context->fsuid) {
+	if (is_key_possessed(key_ref)) {
+		kperm = key->perm >> 24;
+	}
+	else if (key->uid == context->fsuid) {
 		kperm = key->perm >> 16;
 	}
 	else if (key->gid != -1 &&
@@ -121,9 +131,9 @@ static inline int key_task_permission(const struct key *key,
 
 }
 
-extern struct key *lookup_user_key(struct task_struct *context,
-				   key_serial_t id, int create, int partial,
-				   key_perm_t perm);
+extern key_ref_t lookup_user_key(struct task_struct *context,
+				 key_serial_t id, int create, int partial,
+				 key_perm_t perm);
 
 extern long join_session_keyring(const char *name);