1============= 2NFS ID Mapper 3============= 4 5Id mapper is used by NFS to translate user and group ids into names, and to 6translate user and group names into ids. Part of this translation involves 7performing an upcall to userspace to request the information. There are two 8ways NFS could obtain this information: placing a call to /sbin/request-key 9or by placing a call to the rpc.idmap daemon. 10 11NFS will attempt to call /sbin/request-key first. If this succeeds, the 12result will be cached using the generic request-key cache. This call should 13only fail if /etc/request-key.conf is not configured for the id_resolver key 14type, see the "Configuring" section below if you wish to use the request-key 15method. 16 17If the call to /sbin/request-key fails (if /etc/request-key.conf is not 18configured with the id_resolver key type), then the idmapper will ask the 19legacy rpc.idmap daemon for the id mapping. This result will be stored 20in a custom NFS idmap cache. 21 22 23Configuring 24=========== 25 26The file /etc/request-key.conf will need to be modified so /sbin/request-key can 27direct the upcall. The following line should be added: 28 29``#OP TYPE DESCRIPTION CALLOUT INFO PROGRAM ARG1 ARG2 ARG3 ...`` 30``#====== ======= =============== =============== ===============================`` 31``create id_resolver * * /usr/sbin/nfs.idmap %k %d 600`` 32 33 34This will direct all id_resolver requests to the program /usr/sbin/nfs.idmap. 35The last parameter, 600, defines how many seconds into the future the key will 36expire. This parameter is optional for /usr/sbin/nfs.idmap. When the timeout 37is not specified, nfs.idmap will default to 600 seconds. 38 39id mapper uses for key descriptions:: 40 41 uid: Find the UID for the given user 42 gid: Find the GID for the given group 43 user: Find the user name for the given UID 44 group: Find the group name for the given GID 45 46You can handle any of these individually, rather than using the generic upcall 47program. If you would like to use your own program for a uid lookup then you 48would edit your request-key.conf so it look similar to this: 49 50``#OP TYPE DESCRIPTION CALLOUT INFO PROGRAM ARG1 ARG2 ARG3 ...`` 51``#====== ======= =============== =============== ===============================`` 52``create id_resolver uid:* * /some/other/program %k %d 600`` 53``create id_resolver * * /usr/sbin/nfs.idmap %k %d 600`` 54 55 56Notice that the new line was added above the line for the generic program. 57request-key will find the first matching line and corresponding program. In 58this case, /some/other/program will handle all uid lookups and 59/usr/sbin/nfs.idmap will handle gid, user, and group lookups. 60 61See Documentation/security/keys/request-key.rst for more information 62about the request-key function. 63 64 65nfs.idmap 66========= 67 68nfs.idmap is designed to be called by request-key, and should not be run "by 69hand". This program takes two arguments, a serialized key and a key 70description. The serialized key is first converted into a key_serial_t, and 71then passed as an argument to keyctl_instantiate (both are part of keyutils.h). 72 73The actual lookups are performed by functions found in nfsidmap.h. nfs.idmap 74determines the correct function to call by looking at the first part of the 75description string. For example, a uid lookup description will appear as 76"uid:user@domain". 77 78nfs.idmap will return 0 if the key was instantiated, and non-zero otherwise. 79