[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, 29 insertions, 7 deletions

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 90c1506..e6dd366 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -129,7 +129,7 @@ static struct key *__request_key_construction(struct key_type *type,
 
 	/* create a key and add it to the queue */
 	key = key_alloc(type, description,
-			current->fsuid, current->fsgid, KEY_USR_ALL, 0);
+			current->fsuid, current->fsgid, KEY_POS_ALL, 0);
 	if (IS_ERR(key))
 		goto alloc_failed;
 
@@ -365,14 +365,24 @@ struct key *request_key_and_link(struct key_type *type,
 {
 	struct key_user *user;
 	struct key *key;
+	key_ref_t key_ref;
 
 	kenter("%s,%s,%s,%p",
 	       type->name, description, callout_info, dest_keyring);
 
 	/* search all the process keyrings for a key */
-	key = search_process_keyrings(type, description, type->match, current);
+	key_ref = search_process_keyrings(type, description, type->match,
+					  current);
 
-	if (PTR_ERR(key) == -EAGAIN) {
+	kdebug("search 1: %p", key_ref);
+
+	if (!IS_ERR(key_ref)) {
+		key = key_ref_to_ptr(key_ref);
+	}
+	else if (PTR_ERR(key_ref) != -EAGAIN) {
+		key = ERR_PTR(PTR_ERR(key_ref));
+	}
+	else  {
 		/* the search failed, but the keyrings were searchable, so we
 		 * should consult userspace if we can */
 		key = ERR_PTR(-ENOKEY);
@@ -384,7 +394,7 @@ struct key *request_key_and_link(struct key_type *type,
 		if (!user)
 			goto nomem;
 
-		do {
+		for (;;) {
 			if (signal_pending(current))
 				goto interrupted;
 
@@ -397,10 +407,22 @@ struct key *request_key_and_link(struct key_type *type,
 
 			/* someone else made the key we want, so we need to
 			 * search again as it might now be available to us */
-			key = search_process_keyrings(type, description,
-						      type->match, current);
+			key_ref = search_process_keyrings(type, description,
+							  type->match,
+							  current);
+
+			kdebug("search 2: %p", key_ref);
 
-		} while (PTR_ERR(key) == -EAGAIN);
+			if (!IS_ERR(key_ref)) {
+				key = key_ref_to_ptr(key_ref);
+				break;
+			}
+
+			if (PTR_ERR(key_ref) != -EAGAIN) {
+				key = ERR_PTR(PTR_ERR(key_ref));
+				break;
+			}
+		}
 
 		key_user_put(user);