======================
Keys have an owner user ID, a group access ID, and a permissions mask. The mask
-has up to eight bits each for user, group and other access. Only five of each
-set of eight bits are defined. These permissions granted are:
+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:
(*) View
keyring to a key, a process must have Write permission on the keyring and
Link permission on the key.
+ (*) Set Attribute
+
+ This permits a key's UID, GID and permissions mask to be changed.
+
For changing the ownership, group ID or permissions mask, being the owner of
the key or having the sysadmin capability is sufficient.
type, description and permissions. The payload of the key is not available
this way:
- SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY
- 00000001 I----- 39 perm 1f0000 0 0 keyring _uid_ses.0: 1/4
- 00000002 I----- 2 perm 1f0000 0 0 keyring _uid.0: empty
- 00000007 I----- 1 perm 1f0000 0 0 keyring _pid.1: empty
- 0000018d I----- 1 perm 1f0000 0 0 keyring _pid.412: empty
- 000004d2 I--Q-- 1 perm 1f0000 32 -1 keyring _uid.32: 1/4
- 000004d3 I--Q-- 3 perm 1f0000 32 -1 keyring _uid_ses.32: empty
- 00000892 I--QU- 1 perm 1f0000 0 0 user metal:copper: 0
- 00000893 I--Q-N 1 35s 1f0000 0 0 user metal:silver: 0
- 00000894 I--Q-- 1 10h 1f0000 0 0 user metal:gold: 0
+ SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY
+ 00000001 I----- 39 perm 1f3f0000 0 0 keyring _uid_ses.0: 1/4
+ 00000002 I----- 2 perm 1f3f0000 0 0 keyring _uid.0: empty
+ 00000007 I----- 1 perm 1f3f0000 0 0 keyring _pid.1: empty
+ 0000018d I----- 1 perm 1f3f0000 0 0 keyring _pid.412: empty
+ 000004d2 I--Q-- 1 perm 1f3f0000 32 -1 keyring _uid.32: 1/4
+ 000004d3 I--Q-- 3 perm 1f3f0000 32 -1 keyring _uid_ses.32: empty
+ 00000892 I--QU- 1 perm 1f000000 0 0 user metal:copper: 0
+ 00000893 I--Q-N 1 35s 1f3f0000 0 0 user metal:silver: 0
+ 00000894 I--Q-- 1 10h 003f0000 0 0 user metal:gold: 0
The flags are:
KEY_SPEC_USER_KEYRING -4 UID-specific keyring
KEY_SPEC_USER_SESSION_KEYRING -5 UID-session keyring
KEY_SPEC_GROUP_KEYRING -6 GID-specific keyring
+ KEY_SPEC_REQKEY_AUTH_KEY -7 assumed request_key()
+ authorisation key
The main syscalls are:
/sbin/request-key will be invoked in an attempt to obtain a key. The
callout_info string will be passed as an argument to the program.
+ See also Documentation/keys-request-key.txt.
+
The keyctl syscall functions are:
keyring is full, error ENFILE will result.
The link procedure checks the nesting of the keyrings, returning ELOOP if
- it appears to deep or EDEADLK if the link would introduce a cycle.
+ it appears too deep or EDEADLK if the link would introduce a cycle.
+
+ Any links within the keyring to keys that match the new key in terms of
+ type and description will be discarded from the keyring as the new one is
+ added.
(*) Unlink a key or keyring from another keyring:
(*) Read the payload data from a key:
- key_serial_t keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer,
- size_t buflen);
+ long keyctl(KEYCTL_READ, key_serial_t keyring, char *buffer,
+ size_t buflen);
This function attempts to read the payload data from the specified key
into the buffer. The process must have read permission on the key to
(*) Instantiate a partially constructed key.
- key_serial_t keyctl(KEYCTL_INSTANTIATE, key_serial_t key,
- const void *payload, size_t plen,
- key_serial_t keyring);
+ long keyctl(KEYCTL_INSTANTIATE, key_serial_t key,
+ const void *payload, size_t plen,
+ key_serial_t keyring);
If the kernel calls back to userspace to complete the instantiation of a
key, userspace should use this call to supply data for the key before the
(*) Negatively instantiate a partially constructed key.
- key_serial_t keyctl(KEYCTL_NEGATE, key_serial_t key,
- unsigned timeout, key_serial_t keyring);
+ long keyctl(KEYCTL_NEGATE, key_serial_t key,
+ unsigned timeout, key_serial_t keyring);
If the kernel calls back to userspace to complete the instantiation of a
key, userspace should use this call mark the key as negative before the
there is one, otherwise the user default session keyring.
+ (*) Set the timeout on a key.
+
+ long keyctl(KEYCTL_SET_TIMEOUT, key_serial_t key, unsigned timeout);
+
+ This sets or clears the timeout on a key. The timeout can be 0 to clear
+ the timeout or a number of seconds to set the expiry time that far into
+ the future.
+
+ The process must have attribute modification access on a key to set its
+ timeout. Timeouts may not be set with this function on negative, revoked
+ or expired keys.
+
+
+ (*) Assume the authority granted to instantiate a key
+
+ long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key);
+
+ This assumes or divests the authority required to instantiate the
+ specified key. Authority can only be assumed if the thread has the
+ authorisation key associated with the specified key in its keyrings
+ somewhere.
+
+ Once authority is assumed, searches for keys will also search the
+ requester's keyrings using the requester's security label, UID, GID and
+ groups.
+
+ If the requested authority is unavailable, error EPERM will be returned,
+ likewise if the authority has been revoked because the target key is
+ already instantiated.
+
+ If the specified key is 0, then any assumed authority will be divested.
+
+ The assumed authorititive key is inherited across fork and exec.
+
+
===============
KERNEL SERVICES
===============
two different users opening the same file is left to the filesystem author to
solve.
+Note that there are two different types of pointers to keys that may be
+encountered:
+
+ (*) struct key *
+
+ This simply points to the key structure itself. Key structures will be at
+ least four-byte aligned.
+
+ (*) key_ref_t
+
+ This is equivalent to a struct key *, but the least significant bit is set
+ if the caller "possesses" the key. By "possession" it is meant that the
+ calling processes has a searchable link to the key from one of its
+ keyrings. There are three functions for dealing with these:
+
+ key_ref_t make_key_ref(const struct key *key,
+ unsigned long possession);
+
+ struct key *key_ref_to_ptr(const key_ref_t key_ref);
+
+ unsigned long is_key_possessed(const key_ref_t key_ref);
+
+ The first function constructs a key reference from a key pointer and
+ possession information (which must be 0 or 1 and not any other value).
+
+ The second function retrieves the key pointer from a reference and the
+ third retrieves the possession flag.
+
When accessing a key's payload contents, certain precautions must be taken to
prevent access vs modification races. See the section "Notes on accessing
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.
+ See also Documentation/keys-request-key.txt.
+
(*) When it is no longer required, the key should be released using:
void key_put(struct key *key);
- This can be called from interrupt context. If CONFIG_KEYS is not set then
+ Or:
+
+ void key_ref_put(key_ref_t key_ref);
+
+ These can be called from interrupt context. If CONFIG_KEYS is not set then
the argument will not be parsed.
(*) If a keyring was found in the search, this can be further searched by:
- struct key *keyring_search(struct key *keyring,
- const struct key_type *type,
- const char *description)
+ key_ref_t keyring_search(key_ref_t keyring_ref,
+ const struct key_type *type,
+ const char *description)
This searches the keyring tree specified for a matching key. Error ENOKEY
- is returned upon failure. If successful, the returned key will need to be
- released.
+ is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
+ the returned key will need to be released.
+
+ The possession attribute from the keyring reference is used to control
+ access through the permissions mask and is propagated to the returned key
+ reference pointer if successful.
(*) To check the validity of a key, this function can be called:
key->payload.data. One of the following ways must be selected to access the
data:
- (1) Unmodifyable key type.
+ (1) Unmodifiable key type.
If the key type does not have a modify method, then the key's payload can
be accessed without any form of locking, provided that it's known to be
It is safe to sleep in this method.
- (*) int (*duplicate)(struct key *key, const struct key *source);
-
- If this type of key can be duplicated, then this method should be
- provided. It is called to copy the payload attached to the source into the
- new key. The data length on the new key will have been updated and the
- quota adjusted already.
-
- This method will be called with the source key's semaphore read-locked to
- prevent its payload from being changed, thus RCU constraints need not be
- applied to the source key.
-
- This method does not have to lock the destination key in order to attach a
- payload. The fact that KEY_FLAG_INSTANTIATED is not set in key->flags
- prevents anything else from gaining access to the key.
-
- It is safe to sleep in this method.
-
-
(*) int (*update)(struct key *key, const void *data, size_t datalen);
If this type of key can be updated, then this method should be provided.
git.openpandora.org / pandora-kernel.git / blobdiff