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CIFS.UPCALL(8) | System Administration tools | CIFS.UPCALL(8) |
NAME¶
cifs.upcall - Userspace upcall helper for Common Internet File System (CIFS)SYNOPSIS¶
cifs.upcall [--trust-dns|-t] [--version|-v] [--legacy-uid|-l]
[--krb5conf=/path/to/krb5.conf|-k /path/to/krb5.conf]
[--keytab=/path/to/keytab|-K /path/to/keytab] {keyid}
DESCRIPTION¶
This tool is part of the cifs-utils suite. cifs.upcall is a userspace helper program for the linux CIFS client filesystem. There are a number of activities that the kernel cannot easily do itself. This program is a callout program that does these things for the kernel and then returns the result. cifs.upcall is generally intended to be run when the kernel calls request-key(8) for a particular key type. While it can be run directly from the command-line, it´s not generally intended to be run that way.OPTIONS¶
-cThis option is deprecated and is currently ignored.
--krb5conf=/path/to/krb5.conf|-k /path/to/krb5.conf
This option allows administrators to set an alternate
location for the krb5.conf file that cifs.upcall will use.
--keytab=/path/to/keytab|-K /path/to/keytab
This option allows administrators to specify a keytab
file to be used. When a user has no credential cache already established,
cifs.upcall will attempt to use this keytab to acquire them. The default is
the system-wide keytab /etc/krb5.keytab.
--trust-dns|-t
With krb5 upcalls, the name used as the host portion of
the service principal defaults to the hostname portion of the UNC. This option
allows the upcall program to reverse resolve the network address of the server
in order to get the hostname.
This is less secure than not trusting DNS. When using this option, it´s
possible that an attacker could get control of DNS and trick the client into
mounting a different server altogether. It´s preferable to instead add
server principals to the KDC for every possible hostname, but this option
exists for cases where that isn´t possible. The default is to not trust
reverse hostname lookups in this fashion.
--legacy-uid|-l
Traditionally, the kernel has sent only a single uid=
parameter to the upcall for the SPNEGO upcall that´s used to determine
what user's credential cache to use. This parameter is affected by the uid=
mount option, which also governs the ownership of files on the mount.
Newer kernels send a creduid= option as well, which contains what uid it thinks
actually owns the credentials that it´s looking for. At mount time,
this is generally set to the real uid of the user doing the mount. For
multisession mounts, it's set to the fsuid of the mount user. Set this option
if you want cifs.upcall to use the older uid= parameter instead of the
creduid= parameter.
--version|-v
Print version number and exit.
CONFIGURATION FOR KEYCTL¶
cifs.upcall is designed to be called from the kernel via the request-key callout program. This requires that request-key be told where and how to call this program. The current cifs.upcall program handles two different key types: cifs.spnegoThis keytype is for retrieving kerberos session
keys
dns_resolver
This key type is for resolving hostnames into IP
addresses. Support for this key type may eventually be deprecated (see
below).
To make this program useful for CIFS, you´ll need to set up entries for
them in request-key.conf(5). Here´s an example of an entry for each key
type:
#OPERATION TYPE D C PROGRAM ARG1 ARG2... #========= ============= = = ================================ create cifs.spnego * * /usr/sbin/cifs.upcall %k create dns_resolver * * /usr/sbin/cifs.upcall %k
SEE ALSO¶
request-key.conf(5), mount.cifs(8), key.dns_resolver(8)AUTHOR¶
Igor Mammedov wrote the cifs.upcall program. Jeff Layton authored this manpage. The maintainer of the Linux CIFS VFS is Steve French. The Linux CIFS Mailing list is the preferred place to ask questions regarding these programs.02/07/2010 | cifs-utils |