1CIFS.UPCALL(8) System Administration tools CIFS.UPCALL(8)
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6 cifs.upcall - Userspace upcall helper for Common Internet File System
7 (CIFS)
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10 cifs.upcall [--trust-dns|-t] [--version|-v] [--legacy-uid|-l]
11 [--krb5conf=/path/to/krb5.conf|-k /path/to/krb5.conf]
12 [--keytab=/path/to/keytab|-K /path/to/keytab] {keyid}
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15 This tool is part of the cifs-utils suite.
16 cifs.upcall is a userspace helper program for the linux CIFS client
18 filesystem. There are a number of activities that the kernel cannot
19 easily do itself. This program is a callout program that does these
20 things for the kernel and then returns the result.
21 cifs.upcall is generally intended to be run when the kernel calls
23 request-key(8) for a particular key type. While it can be run directly
24 from the command-line, it´s not generally intended to be run that way.
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27 -c
28 This option is deprecated and is currently ignored.
29 --krb5conf=/path/to/krb5.conf|-k /path/to/krb5.conf
31 This option allows administrators to set an alternate location for
32 the krb5.conf file that cifs.upcall will use.
33 --keytab=/path/to/keytab|-K /path/to/keytab
35 This option allows administrators to specify a keytab file to be
36 used. When a user has no credential cache already established,
37 cifs.upcall will attempt to use this keytab to acquire them. The
38 default is the system-wide keytab /etc/krb5.keytab.
39 --trust-dns|-t
41 With krb5 upcalls, the name used as the host portion of the service
42 principal defaults to the hostname portion of the UNC. This option
43 allows the upcall program to reverse resolve the network address of
44 the server in order to get the hostname.
45 This is less secure than not trusting DNS. When using this option,
47 it´s possible that an attacker could get control of DNS and trick
48 the client into mounting a different server altogether. It´s
49 preferable to instead add server principals to the KDC for every
50 possible hostname, but this option exists for cases where that
51 isn´t possible. The default is to not trust reverse hostname
52 lookups in this fashion.
53 --legacy-uid|-l
55 Traditionally, the kernel has sent only a single uid= parameter to
56 the upcall for the SPNEGO upcall that´s used to determine what
57 user's credential cache to use. This parameter is affected by the
58 uid= mount option, which also governs the ownership of files on the
59 mount.
60 Newer kernels send a creduid= option as well, which contains what
62 uid it thinks actually owns the credentials that it´s looking for.
63 At mount time, this is generally set to the real uid of the user
64 doing the mount. For multisession mounts, it's set to the fsuid of
65 the mount user. Set this option if you want cifs.upcall to use the
66 older uid= parameter instead of the creduid= parameter.
67 --version|-v
69 Print version number and exit.
70
72 cifs.upcall is designed to be called from the kernel via the
73 request-key callout program. This requires that request-key be told
74 where and how to call this program. The current cifs.upcall program
75 handles two different key types:
76 cifs.spnego
78 This keytype is for retrieving kerberos session keys
79 dns_resolver
81 This key type is for resolving hostnames into IP addresses. Support
82 for this key type may eventually be deprecated (see below).
83 To make this program useful for CIFS, you´ll need to set up entries for
85 them in request-key.conf(5). Here´s an example of an entry for each key
86 type:
87 #OPERATION TYPE D C PROGRAM ARG1 ARG2...
89 #========= ============= = = ================================
90 create cifs.spnego * * /usr/sbin/cifs.upcall %k
91 create dns_resolver * * /usr/sbin/cifs.upcall %k
92 See request-key.conf(5) for more info on each field.
94 The keyutils package has also started including a dns_resolver handling
96 program as well that is preferred over the one in cifs.upcall. If you
97 are using a keyutils version equal to or greater than 1.5, you should
98 use key.dns_resolver to handle the dns_resolver keytype instead of
99 cifs.upcall. See key.dns_resolver(8) for more info.
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102 request-key.conf(5), mount.cifs(8), key.dns_resolver(8)
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105 Igor Mammedov wrote the cifs.upcall program.
106 Jeff Layton authored this manpage.
108 The maintainer of the Linux CIFS VFS is Steve French.
110 The Linux CIFS Mailing list is the preferred place to ask questions
112 regarding these programs.
113cifs-utils 02/07/2010 CIFS.UPCALL(8)