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.

       --no-env-probe|-E
          Normally,  cifs.upcall  will  probe  the environment variable space of the process that
          initiated the upcall in order to fetch the value of $KRB5CCNAME. This  can  assist  the
          program with finding credential caches in non-default locations. If this option is set,
          then the program won't do this and will rely  on  finding  credcaches  in  the  default
          locations  specified in krb5.conf. Note that this is never performed when the uid is 0.
          The default credcache location is always used when the uid  is  0,  regardless  of  the
          environment variable setting in the process.

       --krb5conf|-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=|-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.upcallprogram 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.UPCALL(8)