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
       -c
	   This 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.spnego
	   This 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 request-key.conf(5) for more info on each field.

       The keyutils package has also started including a dns_resolver handling
       program as well that is preferred over the one in cifs.upcall. If you
       are using a keyutils version equal to or greater than 1.5, you should
       use key.dns_resolver to handle the dns_resolver keytype instead of
       cifs.upcall. See key.dns_resolver(8) for more info.

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.



cifs-utils			  02/07/2010			CIFS.UPCALL(8)