request_key()
asks the kernel to find a key of the given
type
that matches the specified
description
and, if successful, to attach it to the nominated
keyring
and to return its serial number.
request_key()
first recursively searches all the keyrings attached to the calling process in
the order thread-specific keyring, process-specific keyring and then session
keyring for a matching key.
If
request_key()
is called from a program invoked by
request_key()
on behalf of some other process to generate a key, then the keyrings of that
other process will be searched next, using that other process's UID, GID,
groups and security context to control access.
The keys in each keyring searched are checked for a match before any child
keyrings are recursed into. Only keys that are
searchable
for the caller may be found, and only
searchable
keyrings may be searched.
If the key is not found then, if
callout_info
is set, this function will attempt to look further afield. In such a case, the
callout_info
is passed to a userspace service such as
/sbin/request-key
to generate the key.
If that is unsuccessful also, then an error will be returned, and a temporary
negative key will be installed in the nominated
keyring.
This will expire after a few seconds, but will cause subsequent
calls to
request_key()
to fail until it does.
The
keyring
serial number may be that of a valid keyring to which the caller has write
permission, or it may be a special keyring ID:
KEY_SPEC_THREAD_KEYRING
This specifies the caller's thread-specific keyring.
KEY_SPEC_PROCESS_KEYRING
This specifies the caller's process-specific keyring.
KEY_SPEC_SESSION_KEYRING
This specifies the caller's session-specific keyring.
KEY_SPEC_USER_KEYRING
This specifies the caller's UID-specific keyring.
KEY_SPEC_USER_SESSION_KEYRING
This specifies the caller's UID-session keyring.
If a key is created, no matter whether it's a valid key or a negative key, it
will displace any other key of the same type and description from the
destination
keyring.
RETURN VALUE
On success
request_key()
returns the serial number of the key it found.
On error, the value
-1
will be returned and errno will have been set to an appropriate error.
ERRORS
ENOKEY
No matching key was found.
EKEYEXPIRED
An expired key was found, but no replacement could be obtained.
EKEYREVOKED
A revoked key was found, but no replacement could be obtained.
EKEYREJECTED
The attempt to generate a new key was rejected.
ENOMEM
Insufficient memory to create a key.
EINTR
The request was interrupted by a signal.
EDQUOT
The key quota for this user would be exceeded by creating this key or linking
it to the keyring.
EACCES
The keyring wasn't available for modification by the user.
LINKING
Although this is a Linux system call, it is not present in
libc
but can be found rather in
libkeyutils.
When linking,
-lkeyutils
should be specified to the linker.
