| |
| ========= |
| ID Mapper |
| ========= |
| Id mapper is used by NFS to translate user and group ids into names, and to |
| translate user and group names into ids. Part of this translation involves |
| performing an upcall to userspace to request the information. There are two |
| ways NFS could obtain this information: placing a call to /sbin/request-key |
| or by placing a call to the rpc.idmap daemon. |
| |
| NFS will attempt to call /sbin/request-key first. If this succeeds, the |
| result will be cached using the generic request-key cache. This call should |
| only fail if /etc/request-key.conf is not configured for the id_resolver key |
| type, see the "Configuring" section below if you wish to use the request-key |
| method. |
| |
| If the call to /sbin/request-key fails (if /etc/request-key.conf is not |
| configured with the id_resolver key type), then the idmapper will ask the |
| legacy rpc.idmap daemon for the id mapping. This result will be stored |
| in a custom NFS idmap cache. |
| |
| |
| =========== |
| Configuring |
| =========== |
| The file /etc/request-key.conf will need to be modified so /sbin/request-key can |
| direct the upcall. The following line should be added: |
| |
| #OP TYPE DESCRIPTION CALLOUT INFO PROGRAM ARG1 ARG2 ARG3 ... |
| #====== ======= =============== =============== =============================== |
| create id_resolver * * /usr/sbin/nfs.idmap %k %d 600 |
| |
| This will direct all id_resolver requests to the program /usr/sbin/nfs.idmap. |
| The last parameter, 600, defines how many seconds into the future the key will |
| expire. This parameter is optional for /usr/sbin/nfs.idmap. When the timeout |
| is not specified, nfs.idmap will default to 600 seconds. |
| |
| id mapper uses for key descriptions: |
| uid: Find the UID for the given user |
| gid: Find the GID for the given group |
| user: Find the user name for the given UID |
| group: Find the group name for the given GID |
| |
| You can handle any of these individually, rather than using the generic upcall |
| program. If you would like to use your own program for a uid lookup then you |
| would edit your request-key.conf so it look similar to this: |
| |
| #OP TYPE DESCRIPTION CALLOUT INFO PROGRAM ARG1 ARG2 ARG3 ... |
| #====== ======= =============== =============== =============================== |
| create id_resolver uid:* * /some/other/program %k %d 600 |
| create id_resolver * * /usr/sbin/nfs.idmap %k %d 600 |
| |
| Notice that the new line was added above the line for the generic program. |
| request-key will find the first matching line and corresponding program. In |
| this case, /some/other/program will handle all uid lookups and |
| /usr/sbin/nfs.idmap will handle gid, user, and group lookups. |
| |
| See <file:Documentation/security/keys/request-key.rst> for more information |
| about the request-key function. |
| |
| |
| ========= |
| nfs.idmap |
| ========= |
| nfs.idmap is designed to be called by request-key, and should not be run "by |
| hand". This program takes two arguments, a serialized key and a key |
| description. The serialized key is first converted into a key_serial_t, and |
| then passed as an argument to keyctl_instantiate (both are part of keyutils.h). |
| |
| The actual lookups are performed by functions found in nfsidmap.h. nfs.idmap |
| determines the correct function to call by looking at the first part of the |
| description string. For example, a uid lookup description will appear as |
| "uid:user@domain". |
| |
| nfs.idmap will return 0 if the key was instantiated, and non-zero otherwise. |