Ubuntu Manpage: cifs.upcall - Userspace upcall helper for Common Internet File System (CIFS)

Provided by: cifs-utils_6.0-1ubuntu2_amd64

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/...] {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.

--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.

AUTHOR