These files are used by the /sbin/request-key program to determine which program it should run to instantiate a key.
request-key looks for the best match, reading all the following files:
If it doesn't find a match, it will return an error and the kernel will automatically negate the key.
The best match is defined as the line with the shortest wildcard skips, ranking the columns in order left to right. If two lines have the same length skips, then the first read is the one taken.
In the files, any blank line or line beginning with a hash mark '#' is considered to be a comment and ignored.
All other lines are assumed to be command lines with a number of white space separated fields:
<op> <type> <description> <callout-info> <prog> <arg1> <arg2> ...
The first four fields are used to match the parameters passed to request-key by the kernel. op is the operation type; currently the only supported operation is "create".
type, description and callout-info match the three parameters passed to keyctl request2 or the request_key() system call. Each of these may contain one asterisk '*' character as a wildcard anywhere within the string.
Should a match be made, the program specified by <prog> will be exec'd. This must have a fully qualified path name. argv will be set from the part of the program name that follows the last slash '/' character.
If the program name is prefixed with a pipe bar character '|', then the program will be forked and exec'd attached to three pipes. The callout information will be piped to it on it's stdin and the intended payload data will be retrieved from its stdout. Anything sent to stderr will be posted in syslog. If the program exits 0, then /sbin/request-key will attempt to instantiate the key with the data read from stdout. If it fails in any other way, then request-key will attempt to execute the appropriate 'negate' operation command.
The program arguments can be substituted with various macros. Only complete argument substitution is supported - macro substitutions can't be embedded. All macros begin with a percent character '%'. An argument beginning with two percent characters will have one of them discarded.
The following macros are supported:
There's another macro substitution too that permits the interpolation of the contents of a key:
This performs a lookup for a key of the given type and description on the requestor's keyrings, and if found, substitutes the contents for the macro. If not found an error will be logged and the key under construction will be negated.
A basic file will be installed in the /etc. This will contain two debugging lines that can be used to test the installation:
This is set up so that something like:
will create a negative user-defined key, something like:
will create an instantiated user-defined key with "Debug spoon" as the payload, and something like: