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)