KEYCTL_INSTANTIATE(3) Linux Key Management Calls KEYCTL_INSTANTIATE(3)
keyctl_assume_authority, keyctl_instantiate, keyctl_instantiate_iov,
keyctl_reject, keyctl_negate - key instantiation functions
long keyctl_assume_authority(key_serial_t key);
long keyctl_instantiate(key_serial_t key, const void *payload,
size_t plen, key_serial_t keyring);
long keyctl_instantiate_iov(key_serial_t key,
const struct iovec *payload_iov, unsigned ioc,
long keyctl_negate(key_serial_t key, unsigned timeout,
long keyctl_reject(key_serial_t key, unsigned timeout,
unsigned error, key_serial_t keyring);
keyctl_assume_authority() assumes the authority for the calling thread
to deal with and instantiate the specified uninstantiated key.
The calling thread must have the appopriate authorisation key resident
in one of its keyrings for this to succeed, and that authority must not
have been revoked.
The authorising key is allocated by request_key() when it needs to
invoke userspace to generate a key for the requesting process. This is
then attached to one of the keyrings of the userspace process to which
the task of instantiating the key is given:
requester -> request_key() -> instantiator
Calling this function modifies the way request_key() works when called
thereafter by the calling (instantiator) thread; once the authority is
assumed, the keyrings of the initial process are added to the search
path, using the initial process's UID, GID, groups and security con‐
If a thread has multiple instantiations to deal with, it may call this
function to change the authorisation key currently in effect. Supply‐
ing a zero key de-assumes the currently assumed authority.
NOTE! This is a per-thread setting and not a per-process setting so
that a multithreaded process can be used to instantiate several keys at
keyctl_instantiate() instantiates the payload of an uninstantiated key
from the data specified. payload and plen specify the data for the new
payload. payload may be NULL and plen may be zero if the key type per‐
mits that. The key type may reject the data if it's in the wrong for‐
mat or in some other way invalid.
keyctl_instantiate_iov() is similar, but the data is passed in an array
of iovec structs instead of in a flat buffer. payload_iov points to
the base of the array and ioc indicates how many elements there are.
payload_iov may be NULL or ioc may be zero to indicate that no data is
keyctl_reject() marks a key as negatively instantiated and sets the
expiration timer on it. timeout specifies the lifetime of the key in
seconds. error specifies the error to be returned when a search hits
the key (this is typically EKEYREJECTED, EKEYREVOKED or EKEYEXPIRED).
Note that keyctl_reject() falls back to keyctl_negate() if the kernel
does not support it.
keyctl_negate() as keyctl_reject() with an error code of ENOKEY.
Only a key for which authority has been assumed may be instantiated or
negatively instantiated, and once instantiated, the authorisation key
will be revoked and the requesting process will be able to resume.
The destination keyring, if given, is assumed to belong to the initial
requester, and not the instantiating process. Therefore, the special
keyring IDs refer to the requesting process's keyrings, not the call‐
er's, and the requester's UID, etc. will be used to access them.
The destination keyring can be zero if no extra link is desired.
The requester, not the caller, must have write permission on the desti‐
nation for a link to be made there.
On success keyctl_instantiate() returns 0. On error, the value -1 will
be returned and errno will have been set to an appropriate error.
ENOKEY The key or keyring specified is invalid.
The keyring specified has expired.
The key or keyring specified had been revoked, or the authorisa‐
tion has been revoked.
EINVAL The payload data was invalid.
ENOMEM Insufficient memory to store the new payload or to expand the
EDQUOT The key quota for the key's user would be exceeded by increasing
the size of the key to accommodate the new payload or the key
quota for the keyring's user would be exceeded by expanding the
EACCES The key exists, but is not writable by the requester.
This is a library function that can be found in libkeyutils. When
linking, -lkeyutils should be specified to the linker.
keyctl(1), add_key(2), keyctl(2), request_key(2), keyctl(3),
keyrings(7), keyutils(7), request-key(8)
Linux 4 May 2006 KEYCTL_INSTANTIATE(3)