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