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Documentation / filesystems / nfs / idmapper.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:39 EST.

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