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authorDavid Howells <dhowells@redhat.com>2019-06-28 01:03:07 +0300
committerDavid Howells <dhowells@redhat.com>2019-06-28 01:03:07 +0300
commit2e12256b9a76584fa3a6da19210509d4775aee36 (patch)
treed25d8a5868dadab6086230223afeb9d26fac001b /Documentation/security
parenta58946c158a040068e7c94dc1d58bbd273258068 (diff)
downloadlinux-2e12256b9a76584fa3a6da19210509d4775aee36.tar.xz
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>
Diffstat (limited to 'Documentation/security')
-rw-r--r--Documentation/security/keys/core.rst128
-rw-r--r--Documentation/security/keys/request-key.rst9
2 files changed, 106 insertions, 31 deletions
diff --git a/Documentation/security/keys/core.rst b/Documentation/security/keys/core.rst
index 0e74f372e58c..1b3c907980ad 100644
--- a/Documentation/security/keys/core.rst
+++ b/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);
diff --git a/Documentation/security/keys/request-key.rst b/Documentation/security/keys/request-key.rst
index 35f2296b704a..f356fd06c8d5 100644
--- a/Documentation/security/keys/request-key.rst
+++ b/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::