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diff --git a/Documentation/admin-guide/nfs/nfs-idmapper.rst b/Documentation/admin-guide/nfs/nfs-idmapper.rst new file mode 100644 index 000000000000..58b8e63412d5 --- /dev/null +++ b/Documentation/admin-guide/nfs/nfs-idmapper.rst @@ -0,0 +1,78 @@ +============= +NFS 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 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. |