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Subject[PATCH 07/10] keys: Add a keyctl to move a key between keyrings [ver #3]
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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>
---

Documentation/security/keys/core.rst | 21 +++++++
include/linux/key.h | 5 ++
include/uapi/linux/keyctl.h | 3 +
security/keys/compat.c | 3 +
security/keys/internal.h | 3 +
security/keys/keyctl.c | 52 ++++++++++++++++
security/keys/keyring.c | 108 ++++++++++++++++++++++++++++++++++
7 files changed, 195 insertions(+)

diff --git a/Documentation/security/keys/core.rst b/Documentation/security/keys/core.rst
index 9521c4207f01..823d29bf44f7 100644
--- a/Documentation/security/keys/core.rst
+++ b/Documentation/security/keys/core.rst
@@ -577,6 +577,27 @@ The keyctl syscall functions are:
added.


+ * Move a key from one keyring to another::
+
+ long keyctl(KEYCTL_MOVE,
+ key_serial_t id,
+ key_serial_t from_ring_id,
+ key_serial_t to_ring_id,
+ unsigned int flags);
+
+ Move the key specified by "id" from the keyring specified by
+ "from_ring_id" to the keyring specified by "to_ring_id". If the two
+ keyrings are the same, nothing is done.
+
+ "flags" can have KEYCTL_MOVE_EXCL set in it to cause the operation to fail
+ with EEXIST if a matching key exists in the destination keyring, otherwise
+ such a key will be replaced.
+
+ A process must have link permission on the key for this function to be
+ successful and write permission on both keyrings. Any errors that can
+ occur from KEYCTL_LINK also apply on the destination keyring here.
+
+
* Unlink a key or keyring from another keyring::

long keyctl(KEYCTL_UNLINK, key_serial_t keyring, key_serial_t key);
diff --git a/include/linux/key.h b/include/linux/key.h
index 1f09aad1c98c..612e1cf84049 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -310,6 +310,11 @@ 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 f45ee0f69c0c..fd9fb11b312b 100644
--- a/include/uapi/linux/keyctl.h
+++ b/include/uapi/linux/keyctl.h
@@ -67,6 +67,7 @@
#define KEYCTL_PKEY_SIGN 27 /* Create a public key signature */
#define KEYCTL_PKEY_VERIFY 28 /* Verify a public key signature */
#define KEYCTL_RESTRICT_KEYRING 29 /* Restrict keys allowed to link to a keyring */
+#define KEYCTL_MOVE 30 /* Move keys between keyrings */

/* keyctl structures */
struct keyctl_dh_params {
@@ -112,4 +113,6 @@ struct keyctl_pkey_params {
__u32 __spare[7];
};

+#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 9482df601dc3..b326bc4f84d7 100644
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -159,6 +159,9 @@ COMPAT_SYSCALL_DEFINE5(keyctl, u32, option,
return keyctl_pkey_verify(compat_ptr(arg2), compat_ptr(arg3),
compat_ptr(arg4), compat_ptr(arg5));

+ 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 25cdd0cbdc06..b54a58c025ae 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -95,6 +95,8 @@ extern void key_type_put(struct key_type *ktype);

extern int __key_link_lock(struct key *keyring,
const struct keyring_index_key *index_key);
+extern int __key_move_lock(struct key *l_keyring, struct key *u_keyring,
+ const struct keyring_index_key *index_key);
extern int __key_link_begin(struct key *keyring,
const struct keyring_index_key *index_key,
struct assoc_array_edit **_edit);
@@ -217,6 +219,7 @@ 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 0f947bcbad46..bbfe7d92d41c 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -572,6 +572,52 @@ 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))
+ return PTR_ERR(key_ref);
+
+ 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);
+ return ret;
+}
+
/*
* Return a description of a key to userspace.
*
@@ -1772,6 +1818,12 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
(const void __user *)arg4,
(const void __user *)arg5);

+ 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 12acad3db6cf..67066bb58b83 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -1221,6 +1221,40 @@ int __key_link_lock(struct key *keyring,
return 0;
}

+/*
+ * Lock keyrings for move (link/unlink combination).
+ */
+int __key_move_lock(struct key *l_keyring, struct key *u_keyring,
+ const struct keyring_index_key *index_key)
+ __acquires(&l_keyring->sem)
+ __acquires(&u_keyring->sem)
+ __acquires(&keyring_serialise_link_lock)
+{
+ if (l_keyring->type != &key_type_keyring ||
+ u_keyring->type != &key_type_keyring)
+ return -ENOTDIR;
+
+ /* 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 (l_keyring < u_keyring) {
+ down_write(&l_keyring->sem);
+ down_write_nested(&u_keyring->sem, 1);
+ } else {
+ down_write(&u_keyring->sem);
+ down_write_nested(&l_keyring->sem, 1);
+ }
+
+ /* Serialise link/link calls to prevent parallel calls causing a cycle
+ * when linking two keyring in opposite orders.
+ */
+ if (index_key->type == &key_type_keyring)
+ mutex_lock(&keyring_serialise_link_lock);
+
+ return 0;
+}
+
/*
* Preallocate memory so that a key can be linked into to a keyring.
*/
@@ -1494,6 +1528,80 @@ 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 = NULL, *to_edit = NULL;
+ 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);
+
+ ret = __key_move_lock(from_keyring, to_keyring, &key->index_key);
+ if (ret < 0)
+ goto out;
+ ret = __key_unlink_begin(from_keyring, key, &from_edit);
+ if (ret < 0)
+ goto error;
+ ret = __key_link_begin(to_keyring, &key->index_key, &to_edit);
+ if (ret < 0)
+ goto error;
+
+ 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(key, &to_edit);
+error:
+ __key_link_end(to_keyring, &key->index_key, to_edit);
+ __key_unlink_end(from_keyring, key, from_edit);
+out:
+ kleave(" = %d", ret);
+ return ret;
+}
+EXPORT_SYMBOL(key_move);
+
/**
* keyring_clear - Clear a keyring
* @keyring: The keyring to clear.
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