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