[RFC PATCH 23/27] KEYS: Provide KEYCTL_GRANT_PERMISSION

David Howells
2019-02-15T16:12:58Z

Provide a keyctl() operation to grant/remove permissions. The grant
operation, wrapped by libkeyutils, looks like:

int ret = keyctl_grant_permission(key_serial_t key,
enum key_ace_subject_type type,
unsigned int subject,
unsigned int perm);

Where key is the key to be modified, type and subject represent the subject
to which permission is to be granted (or removed) and perm is the set of
permissions to be granted. 0 is returned on success. SET_SECURITY
permission is required for this.

The subject type currently must be KEY_ACE_SUBJ_STANDARD for the moment
(other subject types will come along later).

For subject type KEY_ACE_SUBJ_STANDARD, the following subject values are
available:

KEY_ACE_POSSESSOR The possessor of the key
KEY_ACE_OWNER The owner of the key
KEY_ACE_GROUP The key's group
KEY_ACE_EVERYONE Everyone

perm lists the permissions to be granted:

KEY_ACE_VIEW Can view the key metadata
KEY_ACE_READ Can read the key content
KEY_ACE_WRITE Can update/modify the key content
KEY_ACE_SEARCH Can find the key by searching/requesting
KEY_ACE_LINK Can make a link to the key
KEY_ACE_SET_SECURITY Can set security
KEY_ACE_INVAL Can invalidate
KEY_ACE_REVOKE Can revoke
KEY_ACE_JOIN Can join this keyring
KEY_ACE_CLEAR Can clear this keyring

If an ACE already exists for the subject, then the permissions mask will be
overwritten; if perm is 0, it will be deleted.

Currently, the internal ACL is limited to a maximum of 16 entries.

For example:

int ret = keyctl_grant_permission(key,
KEY_ACE_SUBJ_STANDARD,
KEY_ACE_OWNER,
KEY_ACE_VIEW | KEY_ACE_READ);

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

include/uapi/linux/keyctl.h | 1
security/keys/compat.c | 2 +
security/keys/internal.h | 5 ++
security/keys/keyctl.c | 5 ++
security/keys/permission.c | 119 +++++++++++++++++++++++++++++++++++++++++++
5 files changed, 132 insertions(+)

diff --git a/include/uapi/linux/keyctl.h b/include/uapi/linux/keyctl.h
index 50d7b6ca82ab..045dcbb6bb8d 100644
--- a/include/uapi/linux/keyctl.h
+++ b/include/uapi/linux/keyctl.h
@@ -136,6 +136,7 @@ enum key_ace_standard_subject {
#define KEYCTL_MOVE 33 /* Move keys between keyrings */
#define KEYCTL_FIND_LRU 34 /* Find the least-recently used key in a keyring */
#define KEYCTL_SET_CONTAINER_KEYRING 35 /* Attach a keyring to a container */
+#define KEYCTL_GRANT_PERMISSION 36 /* Grant a permit to a key */

/* keyctl structures */
struct keyctl_dh_params {
diff --git a/security/keys/compat.c b/security/keys/compat.c
index 7990ec026237..953156f94320 100644
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -174,6 +174,8 @@ COMPAT_SYSCALL_DEFINE5(keyctl, u32, option,

case KEYCTL_MOVE:
return keyctl_keyring_move(arg2, arg3, arg4, arg5);
+ case KEYCTL_GRANT_PERMISSION:
+ return keyctl_grant_permission(arg2, arg3, arg4, arg5);

default:
return -EOPNOTSUPP;
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 9f9ecc1810c9..6cd7b5c17298 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -377,6 +377,11 @@ extern long keyctl_find_lru(key_serial_t, const char __user *);
extern long keyctl_set_container_keyring(int, key_serial_t);
#endif

+extern long keyctl_grant_permission(key_serial_t keyid,
+ enum key_ace_subject_type type,
+ unsigned int subject,
+ unsigned int perm);
+
/*
* Debugging key validation
*/
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 2df896bfb8e4..02bd73d5a05a 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1961,6 +1961,11 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
(key_serial_t)arg3,
(key_serial_t)arg4,
(unsigned int)arg5);
+ case KEYCTL_GRANT_PERMISSION:
+ return keyctl_grant_permission((key_serial_t)arg2,
+ (enum key_ace_subject_type)arg3,
+ (unsigned int)arg4,
+ (unsigned int)arg5);

default:
return -EOPNOTSUPP;
diff --git a/security/keys/permission.c b/security/keys/permission.c
index 8dc6e80f6fd0..cb1359f6c668 100644
--- a/security/keys/permission.c
+++ b/security/keys/permission.c
@@ -274,3 +274,122 @@ long key_set_acl(struct key *key, struct key_acl *acl)
key_put_acl(acl);
return 0;
}
+
+/*
+ * Allocate a new ACL with an extra ACE slot.
+ */
+static struct key_acl *key_alloc_acl(const struct key_acl *old_acl, int nr, int skip)
+{
+ struct key_acl *acl;
+ int nr_ace, i, j = 0;
+
+ nr_ace = old_acl->nr_ace + nr;
+ if (nr_ace > 16)
+ return ERR_PTR(-EINVAL);
+
+ acl = kzalloc(struct_size(acl, aces, nr_ace), GFP_KERNEL);
+ if (!acl)
+ return ERR_PTR(-ENOMEM);
+
+ refcount_set(&acl->usage, 1);
+ acl->nr_ace = nr_ace;
+ for (i = 0; i < old_acl->nr_ace; i++) {
+ if (i == skip)
+ continue;
+ acl->aces[j] = old_acl->aces[i];
+ j++;
+ }
+ return acl;
+}
+
+/*
+ * Generate the revised ACL.
+ */
+static long key_change_acl(struct key *key, struct key_ace *new_ace)
+{
+ struct key_acl *acl, *old;
+ int i;
+
+ old = rcu_dereference_protected(key->acl, lockdep_is_held(&key->sem));
+
+ for (i = 0; i < old->nr_ace; i++)
+ if (old->aces[i].type == new_ace->type &&
+ old->aces[i].subject_id == new_ace->subject_id)
+ goto found_match;
+
+ if (new_ace->perm == 0)
+ return 0; /* No permissions to remove. Add deny record? */
+
+ acl = key_alloc_acl(old, 1, -1);
+ if (IS_ERR(acl))
+ return PTR_ERR(acl);
+ acl->aces[i] = *new_ace;
+ goto change;
+
+found_match:
+ if (new_ace->perm == 0)
+ goto delete_ace;
+ if (new_ace->perm == old->aces[i].perm)
+ return 0;
+ acl = key_alloc_acl(old, 0, -1);
+ if (IS_ERR(acl))
+ return PTR_ERR(acl);
+ acl->aces[i].perm = new_ace->perm;
+ goto change;
+
+delete_ace:
+ acl = key_alloc_acl(old, -1, i);
+ if (IS_ERR(acl))
+ return PTR_ERR(acl);
+ goto change;
+
+change:
+ return key_set_acl(key, acl);
+}
+
+/*
+ * Add, alter or remove (if perm == 0) an ACE in a key's ACL.
+ */
+long keyctl_grant_permission(key_serial_t keyid,
+ enum key_ace_subject_type type,
+ unsigned int subject,
+ unsigned int perm)
+{
+ struct key_ace new_ace;
+ struct key *key;
+ key_ref_t key_ref;
+ long ret;
+
+ new_ace.type = type;
+ new_ace.perm = perm;
+
+ switch (type) {
+ case KEY_ACE_SUBJ_STANDARD:
+ if (subject >= nr__key_ace_standard_subject)
+ return -ENOENT;
+ new_ace.subject_id = subject;
+ break;
+
+ default:
+ return -ENOENT;
+ }
+
+ key_ref = lookup_user_key(keyid, KEY_LOOKUP_PARTIAL, KEY_NEED_SETSEC);
+ if (IS_ERR(key_ref)) {
+ ret = PTR_ERR(key_ref);
+ goto error;
+ }
+
+ key = key_ref_to_ptr(key_ref);
+
+ down_write(&key->sem);
+
+ /* If we're not the sysadmin, we can only change a key that we own */
+ ret = -EACCES;
+ if (capable(CAP_SYS_ADMIN) || uid_eq(key->uid, current_fsuid()))
+ ret = key_change_acl(key, &new_ace);
+ up_write(&key->sem);
+ key_put(key);
+error:
+ return ret;
+}