keys: Replace uid/gid/perm permissions checking with an ACL

Replace the uid/gid/perm permissions checking on a key with an ACL to allow
the SETATTR and SEARCH permissions to be split.  This will also allow a
greater range of subjects to represented.

============
WHY DO THIS?
============

The problem is that SETATTR and SEARCH cover a slew of actions, not all of
which should be grouped together.

For SETATTR, this includes actions that are about controlling access to a
key:

 (1) Changing a key's ownership.

 (2) Changing a key's security information.

 (3) Setting a keyring's restriction.

And actions that are about managing a key's lifetime:

 (4) Setting an expiry time.

 (5) Revoking a key.

and (proposed) managing a key as part of a cache:

 (6) Invalidating a key.

Managing a key's lifetime doesn't really have anything to do with
controlling access to that key.

Expiry time is awkward since it's more about the lifetime of the content
and so, in some ways goes better with WRITE permission.  It can, however,
be set unconditionally by a process with an appropriate authorisation token
for instantiating a key, and can also be set by the key type driver when a
key is instantiated, so lumping it with the access-controlling actions is
probably okay.

As for SEARCH permission, that currently covers:

 (1) Finding keys in a keyring tree during a search.

 (2) Permitting keyrings to be joined.

 (3) Invalidation.

But these don't really belong together either, since these actions really
need to be controlled separately.

Finally, there are number of special cases to do with granting the
administrator special rights to invalidate or clear keys that I would like
to handle with the ACL rather than key flags and special checks.


===============
WHAT IS CHANGED
===============

The SETATTR permission is split to create two new permissions:

 (1) SET_SECURITY - which allows the key's owner, group and ACL to be
     changed and a restriction to be placed on a keyring.

 (2) REVOKE - which allows a key to be revoked.

The SEARCH permission is split to create:

 (1) SEARCH - which allows a keyring to be search and a key to be found.

 (2) JOIN - which allows a keyring to be joined as a session keyring.

 (3) INVAL - which allows a key to be invalidated.

The WRITE permission is also split to create:

 (1) WRITE - which allows a key's content to be altered and links to be
     added, removed and replaced in a keyring.

 (2) CLEAR - which allows a keyring to be cleared completely.  This is
     split out to make it possible to give just this to an administrator.

 (3) REVOKE - see above.


Keys acquire ACLs which consist of a series of ACEs, and all that apply are
unioned together.  An ACE specifies a subject, such as:

 (*) Possessor - permitted to anyone who 'possesses' a key
 (*) Owner - permitted to the key owner
 (*) Group - permitted to the key group
 (*) Everyone - permitted to everyone

Note that 'Other' has been replaced with 'Everyone' on the assumption that
you wouldn't grant a permit to 'Other' that you wouldn't also grant to
everyone else.

Further subjects may be made available by later patches.

The ACE also specifies a permissions mask.  The set of permissions is now:

	VIEW		Can view the key metadata
	READ		Can read the key content
	WRITE		Can update/modify the key content
	SEARCH		Can find the key by searching/requesting
	LINK		Can make a link to the key
	SET_SECURITY	Can change owner, ACL, expiry
	INVAL		Can invalidate
	REVOKE		Can revoke
	JOIN		Can join this keyring
	CLEAR		Can clear this keyring


The KEYCTL_SETPERM function is then deprecated.

The KEYCTL_SET_TIMEOUT function then is permitted if SET_SECURITY is set,
or if the caller has a valid instantiation auth token.

The KEYCTL_INVALIDATE function then requires INVAL.

The KEYCTL_REVOKE function then requires REVOKE.

The KEYCTL_JOIN_SESSION_KEYRING function then requires JOIN to join an
existing keyring.

The JOIN permission is enabled by default for session keyrings and manually
created keyrings only.


======================
BACKWARD COMPATIBILITY
======================

To maintain backward compatibility, KEYCTL_SETPERM will translate the
permissions mask it is given into a new ACL for a key - unless
KEYCTL_SET_ACL has been called on that key, in which case an error will be
returned.

It will convert possessor, owner, group and other permissions into separate
ACEs, if each portion of the mask is non-zero.

SETATTR permission turns on all of INVAL, REVOKE and SET_SECURITY.  WRITE
permission turns on WRITE, REVOKE and, if a keyring, CLEAR.  JOIN is turned
on if a keyring is being altered.

The KEYCTL_DESCRIBE function translates the ACL back into a permissions
mask to return depending on possessor, owner, group and everyone ACEs.

It will make the following mappings:

 (1) INVAL, JOIN -> SEARCH

 (2) SET_SECURITY -> SETATTR

 (3) REVOKE -> WRITE if SETATTR isn't already set

 (4) CLEAR -> WRITE

Note that the value subsequently returned by KEYCTL_DESCRIBE may not match
the value set with KEYCTL_SETATTR.


=======
TESTING
=======

This passes the keyutils testsuite for all but a couple of tests:

 (1) tests/keyctl/dh_compute/badargs: The first wrong-key-type test now
     returns EOPNOTSUPP rather than ENOKEY as READ permission isn't removed
     if the type doesn't have ->read().  You still can't actually read the
     key.

 (2) tests/keyctl/permitting/valid: The view-other-permissions test doesn't
     work as Other has been replaced with Everyone in the ACL.

Signed-off-by: David Howells <dhowells@redhat.com>

Author: dhowells

Documentation/security/keys/core.rst

@@ -57,9 +57,9 @@ Each key has a number of attributes:
      type provides an operation to perform a match between the description on a
      key and a criterion string.
 
-  *  Each key has an owner user ID, a group ID and a permissions mask. These
-     are used to control what a process may do to a key from userspace, and
-     whether a kernel service will be able to find the key.
+  *  Each key has an owner user ID, a group ID and an ACL.  These are used to
+     control what a process may do to a key from userspace, and whether a
+     kernel service will be able to find the key.
 
   *  Each key can be set to expire at a specific time by the key type's
      instantiation function. Keys can also be immortal.
@@ -198,43 +198,110 @@ The key service provides a number of features besides keys:
 Key Access Permissions
 ======================
 
-Keys have an owner user ID, a group access ID, and a permissions mask. The mask
-has up to eight bits each for possessor, user, group and other access. Only
-six of each set of eight bits are defined. These permissions granted are:
+Keys have an owner user ID, a group ID and an ACL.  The ACL is made up of a
+sequence of ACEs that each contain three elements:
 
-  *  View
+  * The type of subject.
+  * The subject.
 
-     This permits a key or keyring's attributes to be viewed - including key
-     type and description.
+    These two together indicate the subject to whom the permits are granted.
+    The type can be one of:
 
-  *  Read
+     * ``KEY_ACE_SUBJ_STANDARD``
 
-     This permits a key's payload to be viewed or a keyring's list of linked
-     keys.
+       The subject is a standard 'macro' type.  The subject can be one of:
+
+        * ``KEY_ACE_EVERYONE``
+
+	  The permits are granted to everyone.  It replaces the old 'other'
+	  type on the assumption that you wouldn't grant a permission to other
+	  that you you wouldn't grant to everyone else.
+
+	* ``KEY_ACE_OWNER``
+
+	  The permits are granted to the owner of the key (key->uid).
+
+	* ``KEY_ACE_GROUP``
+
+	  The permits are granted to the key's group (key->gid).
+
+	* ``KEY_ACE_POSSESSOR``
+
+	  The permits are granted to anyone who possesses the key.
+
+  * The set of permits granted to the subject.  These include:
+
+     * ``KEY_ACE_VIEW``
+
+       This permits a key or keyring's attributes to be viewed - including the
+       key type and description.
+
+     * ``KEY_ACE_READ``
+
+       This permits a key's payload to be viewed or a keyring's list of linked
+       keys.
 
-  *  Write
+     * ``KEY_ACE_WRITE``
 
-     This permits a key's payload to be instantiated or updated, or it allows a
-     link to be added to or removed from a keyring.
+       This permits a key's payload to be instantiated or updated, or it allows
+       a link to be added to or removed from a keyring.
 
-  *  Search
+     * ``KEY_ACE_SEARCH``
 
-     This permits keyrings to be searched and keys to be found. Searches can
-     only recurse into nested keyrings that have search permission set.
+       This permits keyrings to be searched and keys to be found. Searches can
+       only recurse into nested keyrings that have search permission set.
 
-  *  Link
+     * ``KEY_ACE_LINK``
 
-     This permits a key or keyring to be linked to. To create a link from a
-     keyring to a key, a process must have Write permission on the keyring and
-     Link permission on the key.
+       This permits a key or keyring to be linked to. To create a link from a
+       keyring to a key, a process must have Write permission on the keyring
+       and Link permission on the key.
 
-  *  Set Attribute
+     * ``KEY_ACE_SET_SECURITY``
 
-     This permits a key's UID, GID and permissions mask to be changed.
+       This permits a key's UID, GID and permissions mask to be changed.
+
+     * ``KEY_ACE_INVAL``
+
+       This permits a key to be invalidated with KEYCTL_INVALIDATE.
+
+     * ``KEY_ACE_REVOKE``
+
+       This permits a key to be revoked with KEYCTL_REVOKE.
+
+     * ``KEY_ACE_JOIN``
+
+       This permits a keyring to be joined as a session by
+       KEYCTL_JOIN_SESSION_KEYRING or KEYCTL_SESSION_TO_PARENT.
+
+     * ``KEY_ACE_CLEAR``
+
+       This permits a keyring to be cleared.
 
 For changing the ownership, group ID or permissions mask, being the owner of
 the key or having the sysadmin capability is sufficient.
 
+The legacy KEYCTL_SETPERM and KEYCTL_DESCRIBE functions can only see/generate
+View, Read, Write, Search, Link and SetAttr permits, and do this for each of
+possessor, user, group and other permission sets as a 32-bit flag mask.  These
+will be approximated/inferred:
+
+	SETPERM Permit	Implied ACE Permit
+	===============	=======================
+	Search		Inval, Join
+	Write		Revoke, Clear
+	Setattr		Set Security, Revoke
+
+	ACE Permit	Described as
+	===============	=======================
+	Inval		Search
+	Join		Search
+	Revoke		Write (unless Setattr)
+	Clear		write
+	Set Security	Setattr
+
+'Other' will be approximated as/inferred from the 'Everyone' subject.
+
 
 SELinux Support
 ===============
@@ -1084,7 +1151,8 @@ payload contents" for more information.
 
 	struct key *request_key(const struct key_type *type,
 				const char *description,
-				const char *callout_info);
+				const char *callout_info,
+				struct key_acl *acl);
 
     This is used to request a key or keyring with a description that matches
     the description specified according to the key type's match_preparse()
@@ -1099,6 +1167,8 @@ payload contents" for more information.
     If successful, the key will have been attached to the default keyring for
     implicitly obtained request-key keys, as set by KEYCTL_SET_REQKEY_KEYRING.
 
+    If a key is created, it will be given the specified ACL.
+
     See also Documentation/security/keys/request-key.rst.
 
 
@@ -1107,7 +1177,8 @@ payload contents" for more information.
 	struct key *request_key_tag(const struct key_type *type,
 				    const char *description,
 				    struct key_tag *domain_tag,
-				    const char *callout_info);
+				    const char *callout_info,
+				    struct key_acl *acl);
 
     This is identical to request_key(), except that a domain tag may be
     specifies that causes search algorithm to only match keys matching that
@@ -1122,7 +1193,8 @@ payload contents" for more information.
 					     struct key_tag *domain_tag,
 					     const void *callout_info,
 					     size_t callout_len,
-					     void *aux);
+					     void *aux,
+					     struct key_acl *acl);
 
     This is identical to request_key_tag(), except that the auxiliary data is
     passed to the key_type->request_key() op if it exists, and the
@@ -1195,7 +1267,7 @@ payload contents" for more information.
 
 	struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
 				  const struct cred *cred,
-				  key_perm_t perm,
+				  struct key_acl *acl,
 				  struct key_restriction *restrict_link,
 				  unsigned long flags,
 				  struct key *dest);

Documentation/security/keys/request-key.rst

@@ -11,14 +11,16 @@ The process starts by either the kernel requesting a service by calling
 
 	struct key *request_key(const struct key_type *type,
 				const char *description,
-				const char *callout_info);
+				const char *callout_info,
+				struct key_acl *acl);
 
 or::
 
 	struct key *request_key_tag(const struct key_type *type,
 				    const char *description,
 				    const struct key_tag *domain_tag,
-				    const char *callout_info);
+				    const char *callout_info,
+				    struct key_acl *acl);
 
 or::
 
@@ -27,7 +29,8 @@ or::
 					     const struct key_tag *domain_tag,
 					     const char *callout_info,
 					     size_t callout_len,
-					     void *aux);
+					     void *aux,
+					     struct key_acl *acl);
 
 or::
 

certs/blacklist.c

@@ -93,8 +93,7 @@ int mark_hash_blacklisted(const char *hash)
 				   hash,
 				   NULL,
 				   0,
-				   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
-				    KEY_USR_VIEW),
+				   &internal_key_acl,
 				   KEY_ALLOC_NOT_IN_QUOTA |
 				   KEY_ALLOC_BUILT_IN);
 	if (IS_ERR(key)) {
@@ -153,9 +152,7 @@ static int __init blacklist_init(void)
 		keyring_alloc(".blacklist",
 			      KUIDT_INIT(0), KGIDT_INIT(0),
 			      current_cred(),
-			      (KEY_POS_ALL & ~KEY_POS_SETATTR) |
-			      KEY_USR_VIEW | KEY_USR_READ |
-			      KEY_USR_SEARCH,
+			      &internal_keyring_acl,
 			      KEY_ALLOC_NOT_IN_QUOTA |
 			      KEY_FLAG_KEEP,
 			      NULL, NULL);

certs/system_keyring.c

@@ -103,9 +103,7 @@ static __init int system_trusted_keyring_init(void)
 	builtin_trusted_keys =
 		keyring_alloc(".builtin_trusted_keys",
 			      KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
-			      ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
-			      KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH),
-			      KEY_ALLOC_NOT_IN_QUOTA,
+			      &internal_key_acl, KEY_ALLOC_NOT_IN_QUOTA,
 			      NULL, NULL);
 	if (IS_ERR(builtin_trusted_keys))
 		panic("Can't allocate builtin trusted keyring\n");
@@ -114,10 +112,7 @@ static __init int system_trusted_keyring_init(void)
 	secondary_trusted_keys =
 		keyring_alloc(".secondary_trusted_keys",
 			      KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
-			      ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
-			       KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH |
-			       KEY_USR_WRITE),
-			      KEY_ALLOC_NOT_IN_QUOTA,
+			      &internal_writable_keyring_acl, KEY_ALLOC_NOT_IN_QUOTA,
 			      get_builtin_and_secondary_restriction(),
 			      NULL);
 	if (IS_ERR(secondary_trusted_keys))
@@ -167,8 +162,7 @@ static __init int load_system_certificate_list(void)
 					   NULL,
 					   p,
 					   plen,
-					   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
-					   KEY_USR_VIEW | KEY_USR_READ),
+					   &internal_key_acl,
 					   KEY_ALLOC_NOT_IN_QUOTA |
 					   KEY_ALLOC_BUILT_IN |
 					   KEY_ALLOC_BYPASS_RESTRICTION);

drivers/md/dm-crypt.c

@@ -2035,7 +2035,7 @@ static int crypt_set_keyring_key(struct crypt_config *cc, const char *key_string
 		return -ENOMEM;
 
 	key = request_key(key_string[0] == 'l' ? &key_type_logon : &key_type_user,
-			  key_desc + 1, NULL);
+			  key_desc + 1, NULL, NULL);
 	if (IS_ERR(key)) {
 		kzfree(new_key_string);
 		return PTR_ERR(key);

drivers/nvdimm/security.c

@@ -55,7 +55,7 @@ static struct key *nvdimm_request_key(struct nvdimm *nvdimm)
 	struct device *dev = &nvdimm->dev;
 
 	sprintf(desc, "%s%s", NVDIMM_PREFIX, nvdimm->dimm_id);
-	key = request_key(&key_type_encrypted, desc, "");
+	key = request_key(&key_type_encrypted, desc, "", NULL);
 	if (IS_ERR(key)) {
 		if (PTR_ERR(key) == -ENOKEY)
 			dev_dbg(dev, "request_key() found no key\n");

fs/afs/security.c

@@ -32,7 +32,7 @@ struct key *afs_request_key(struct afs_cell *cell)
 
 	_debug("key %s", cell->anonymous_key->description);
 	key = request_key(&key_type_rxrpc, cell->anonymous_key->description,
-			  NULL);
+			  NULL, NULL);
 	if (IS_ERR(key)) {
 		if (PTR_ERR(key) != -ENOKEY) {
 			_leave(" = %ld", PTR_ERR(key));

fs/cifs/cifs_spnego.c

@@ -32,6 +32,25 @@
 #include "cifsproto.h"
 static const struct cred *spnego_cred;
 
+static struct key_acl cifs_spnego_key_acl = {
+	.usage	= REFCOUNT_INIT(1),
+	.nr_ace	= 2,
+	.possessor_viewable = true,
+	.aces = {
+		KEY_POSSESSOR_ACE(KEY_ACE_VIEW | KEY_ACE_SEARCH | KEY_ACE_READ),
+		KEY_OWNER_ACE(KEY_ACE_VIEW),
+	}
+};
+
+static struct key_acl cifs_spnego_keyring_acl = {
+	.usage	= REFCOUNT_INIT(1),
+	.nr_ace	= 2,
+	.aces = {
+		KEY_POSSESSOR_ACE(KEY_ACE_SEARCH | KEY_ACE_WRITE),
+		KEY_OWNER_ACE(KEY_ACE_VIEW | KEY_ACE_READ | KEY_ACE_CLEAR),
+	}
+};
+
 /* create a new cifs key */
 static int
 cifs_spnego_key_instantiate(struct key *key, struct key_preparsed_payload *prep)
@@ -170,7 +189,8 @@ cifs_get_spnego_key(struct cifs_ses *sesInfo)
 
 	cifs_dbg(FYI, "key description = %s\n", description);
 	saved_cred = override_creds(spnego_cred);
-	spnego_key = request_key(&cifs_spnego_key_type, description, "");
+	spnego_key = request_key(&cifs_spnego_key_type, description, "",
+				 &cifs_spnego_key_acl);
 	revert_creds(saved_cred);
 
 #ifdef CONFIG_CIFS_DEBUG2
@@ -207,8 +227,7 @@ init_cifs_spnego(void)
 
 	keyring = keyring_alloc(".cifs_spnego",
 				GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
-				(KEY_POS_ALL & ~KEY_POS_SETATTR) |
-				KEY_USR_VIEW | KEY_USR_READ,
+				&cifs_spnego_keyring_acl,
 				KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
 	if (IS_ERR(keyring)) {
 		ret = PTR_ERR(keyring);