[RFC PATCH 17/27] keys: Add a keyctl to move a key between keyrings

David Howells
2019-02-15T16:10:16Z

Add a keyctl to atomically move a link to a key from one keyring to
another. The key must exist in "from" keyring and a flag can be given to
cause the operation to fail if there's a matching key already in the "to"
keyring.

This can be done with:

keyctl(KEYCTL_MOVE,
key_serial_t key,
key_serial_t from_keyring,
key_serial_t to_keyring,
unsigned int flags);

The key being moved must grant Link permission and both keyrings must grant
Write permission.

flags should be 0 or KEYCTL_MOVE_EXCL, with the latter preventing
displacement of a matching key from the "to" keyring.

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

include/linux/key.h | 5 ++
include/uapi/linux/keyctl.h | 3 +
security/keys/compat.c | 3 +
security/keys/internal.h | 1
security/keys/keyctl.c | 55 +++++++++++++++++++++++++++
security/keys/keyring.c | 88 +++++++++++++++++++++++++++++++++++++++++++
6 files changed, 155 insertions(+)

diff --git a/include/linux/key.h b/include/linux/key.h
index 82eb1b8d6336..165f842ec042 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -335,6 +335,11 @@ extern int key_update(key_ref_t key,
extern int key_link(struct key *keyring,
struct key *key);

+extern int key_move(struct key *key,
+ struct key *from_keyring,
+ struct key *to_keyring,
+ unsigned int flags);
+
extern int key_unlink(struct key *keyring,
struct key *key);

diff --git a/include/uapi/linux/keyctl.h b/include/uapi/linux/keyctl.h
index bb075ad1827d..425bbd9612c4 100644
--- a/include/uapi/linux/keyctl.h
+++ b/include/uapi/linux/keyctl.h
@@ -70,6 +70,7 @@
#define KEYCTL_WATCH_KEY 30 /* Watch a key or ring of keys for changes */
#define KEYCTL_CONTAINER_INTERCEPT 31 /* Intercept upcalls inside a container */
#define KEYCTL_QUERY_REQUEST_KEY_AUTH 32 /* Query a request_key_auth key */
+#define KEYCTL_MOVE 33 /* Move keys between keyrings */

/* keyctl structures */
struct keyctl_dh_params {
@@ -126,4 +127,6 @@ struct keyctl_query_request_key_auth {
__u64 spare[1];
};

+#define KEYCTL_MOVE_EXCL 0x00000001 /* Do not displace from the to-keyring */
+
#endif /* _LINUX_KEYCTL_H */
diff --git a/security/keys/compat.c b/security/keys/compat.c
index 30055fc2b629..ed36efa13c48 100644
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -168,6 +168,9 @@ COMPAT_SYSCALL_DEFINE5(keyctl, u32, option,
return keyctl_query_request_key_auth(arg2, compat_ptr(arg3));
#endif

+ case KEYCTL_MOVE:
+ return keyctl_keyring_move(arg2, arg3, arg4, arg5);
+
default:
return -EOPNOTSUPP;
}
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 40846657aebd..bad4a8038a99 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -242,6 +242,7 @@ extern long keyctl_update_key(key_serial_t, const void __user *, size_t);
extern long keyctl_revoke_key(key_serial_t);
extern long keyctl_keyring_clear(key_serial_t);
extern long keyctl_keyring_link(key_serial_t, key_serial_t);
+extern long keyctl_keyring_move(key_serial_t, key_serial_t, key_serial_t, unsigned int);
extern long keyctl_keyring_unlink(key_serial_t, key_serial_t);
extern long keyctl_describe_key(key_serial_t, char __user *, size_t);
extern long keyctl_keyring_search(key_serial_t, const char __user *,
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index a19efc60944d..6057b810c611 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -572,6 +572,55 @@ long keyctl_keyring_unlink(key_serial_t id, key_serial_t ringid)
return ret;
}

+/*
+ * Move a link to a key from one keyring to another, displacing any matching
+ * key from the destination keyring.
+ *
+ * The key must grant the caller Link permission and both keyrings must grant
+ * the caller Write permission. There must also be a link in the from keyring
+ * to the key. If both keyrings are the same, nothing is done.
+ *
+ * If successful, 0 will be returned.
+ */
+long keyctl_keyring_move(key_serial_t id, key_serial_t from_ringid,
+ key_serial_t to_ringid, unsigned int flags)
+{
+ key_ref_t key_ref, from_ref, to_ref;
+ long ret;
+
+ if (flags & ~KEYCTL_MOVE_EXCL)
+ return -EINVAL;
+
+ key_ref = lookup_user_key(id, KEY_LOOKUP_CREATE, KEY_NEED_LINK);
+ if (IS_ERR(key_ref)) {
+ ret = PTR_ERR(key_ref);
+ goto error;
+ }
+
+ from_ref = lookup_user_key(from_ringid, 0, KEY_NEED_WRITE);
+ if (IS_ERR(from_ref)) {
+ ret = PTR_ERR(from_ref);
+ goto error2;
+ }
+
+ to_ref = lookup_user_key(to_ringid, KEY_LOOKUP_CREATE, KEY_NEED_WRITE);
+ if (IS_ERR(to_ref)) {
+ ret = PTR_ERR(to_ref);
+ goto error3;
+ }
+
+ ret = key_move(key_ref_to_ptr(key_ref), key_ref_to_ptr(from_ref),
+ key_ref_to_ptr(to_ref), flags);
+
+ key_ref_put(to_ref);
+error3:
+ key_ref_put(from_ref);
+error2:
+ key_ref_put(key_ref);
+error:
+ return ret;
+}
+
/*
* Return a description of a key to userspace.
*
@@ -1869,6 +1918,12 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
(struct keyctl_query_request_key_auth __user *)arg3);
#endif

+ case KEYCTL_MOVE:
+ return keyctl_keyring_move((key_serial_t)arg2,
+ (key_serial_t)arg3,
+ (key_serial_t)arg4,
+ (unsigned int)arg5);
+
default:
return -EOPNOTSUPP;
}
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 1334ed97e530..14df79814ea0 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -1504,6 +1504,94 @@ int key_unlink(struct key *keyring, struct key *key)
}
EXPORT_SYMBOL(key_unlink);

+/**
+ * key_move - Move a key from one keyring to another
+ * @key: The key to move
+ * @from_keyring: The keyring to remove the link from.
+ * @to_keyring: The keyring to make the link in.
+ * @flags: Qualifying flags, such as KEYCTL_MOVE_EXCL.
+ *
+ * Make a link in @to_keyring to a key, such that the keyring holds a reference
+ * on that key and the key can potentially be found by searching that keyring
+ * whilst simultaneously removing a link to the key from @from_keyring.
+ *
+ * This function will write-lock both keyring's semaphores and will consume
+ * some of the user's key data quota to hold the link on @to_keyring.
+ *
+ * Returns 0 if successful, -ENOTDIR if either keyring isn't a keyring,
+ * -EKEYREVOKED if either keyring has been revoked, -ENFILE if the second
+ * keyring is full, -EDQUOT if there is insufficient key data quota remaining
+ * to add another link or -ENOMEM if there's insufficient memory. If
+ * KEYCTL_MOVE_EXCL is set, then -EEXIST will be returned if there's already a
+ * matching key in @to_keyring.
+ *
+ * It is assumed that the caller has checked that it is permitted for a link to
+ * be made (the keyring should have Write permission and the key Link
+ * permission).
+ */
+int key_move(struct key *key,
+ struct key *from_keyring,
+ struct key *to_keyring,
+ unsigned int flags)
+{
+ struct assoc_array_edit *from_edit, *to_edit;
+ int ret;
+
+ kenter("%d,%d,%d", key->serial, from_keyring->serial, to_keyring->serial);
+
+ if (from_keyring == to_keyring)
+ return 0;
+
+ key_check(key);
+ key_check(from_keyring);
+ key_check(to_keyring);
+
+ /* We have to be very careful here to take the keyring locks in the
+ * right order, lest we open ourselves to deadlocking against another
+ * move operation.
+ */
+ if (from_keyring < to_keyring) {
+ ret = __key_unlink_begin(from_keyring, 0, key, &from_edit);
+ if (ret < 0)
+ goto out;
+ ret = __key_link_begin(to_keyring, 1, &key->index_key, &to_edit);
+ if (ret < 0) {
+ assoc_array_cancel_edit(from_edit);
+ goto out;
+ }
+ } else {
+ ret = __key_link_begin(to_keyring, 0, &key->index_key, &to_edit);
+ if (ret < 0)
+ goto out;
+ ret = __key_unlink_begin(from_keyring, 1, key, &from_edit);
+ if (ret < 0) {
+ __key_link_end(to_keyring, &key->index_key, to_edit);
+ goto out;
+ }
+ }
+
+ ret = -EEXIST;
+ if (to_edit->dead_leaf && (flags & KEYCTL_MOVE_EXCL))
+ goto error;
+
+ ret = __key_link_check_restriction(to_keyring, key);
+ if (ret < 0)
+ goto error;
+ ret = __key_link_check_live_key(to_keyring, key);
+ if (ret < 0)
+ goto error;
+
+ __key_unlink(from_keyring, key, &from_edit);
+ __key_link(to_keyring, key, &to_edit);
+error:
+ __key_unlink_end(from_keyring, key, from_edit);
+ __key_link_end(to_keyring, &key->index_key, to_edit);
+out:
+ kleave(" = %d", ret);
+ return ret;
+}
+EXPORT_SYMBOL(key_move);
+
/**
* keyring_clear - Clear a keyring
* @keyring: The keyring to clear.