mirror of https://github.com/rd235/cado
141 lines
4.3 KiB
Groff
141 lines
4.3 KiB
Groff
.TH SCADO 1 "June 23, 2016" "VirtualSquare Labs"
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.SH NAME
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scado \- Script Capability Ambient DO
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.SH SYNOPSIS
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.B scado
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.B -D
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.B -e
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.B -l
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.br
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.B scado
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.B -u
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.I command
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.B -U
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.br
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.B scado
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.B -h
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.SH DESCRIPTION
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\fBcado(1)\fR allows the system administrator to delegate capabilities to users.
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Users can grant a subset of these ambient capabilities to trusted programs.
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Each user can define their own list of trusted programs and which capabilities to grant, using a scado file.
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\fBcado -S\fR or \fBcado --scado\fR run those trusted programs without any further authentication.
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In this way it is also possible to run programs requiring specific capabilities within a bash script.
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\fBScado\fR is the command a user can run to create, edit, check or delete their own scado file.
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Each line of a scado file file has the following syntax:
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.br
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.RS 4
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.I path_of_the_executable_file : capability_list
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.RE
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.br
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or
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.br
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.RS 4
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.I path_of_the_executable_file : capability_list : sha256_digest_of_the_executable
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.RE
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.br
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(See the EXAMPLES section at the end of the man page for more info. All the trailing part of a line following a # sign is a comment.).
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The \fIpath_of_the_executable_file\fR must be absolute.
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The \fIcapability_list\fR is a comma separated list of capability names or capability
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masks. For brevity, the \fBcap_\fR prefix of capabilities names can be omitted
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(e.g. \fBnet_admin\fR and \fBcap_net_admin\fR have the same meaning).
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The \fIsha256_digest_of_the_executable\fR prevents \fITOCTTOU\fR attacks. When a user
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wants to run the file at \fIpath_of_the_executable_file\fR granting it some of
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the capabilities in the \fIcapability_list\fR, the permission is denied if
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its sha256 digest does not match \fIsha256_digest_of_the_executable\fR.
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If there are only two colon (\fB:\fR) separated fields in a line, it means that
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the user trusts a priori the integrity of the file whose pathname is \fIpath_of_the_executable_file\fR.
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It can be, for example, a program in /bin or /usr/bin not modifiable by users.
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If there are three fields (i.e. two colon characters), it means that the user wants the
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cryptographic digest check on the executable file integrity.
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When a user edits their scado file, if the field (\fIsha256_digest_of_the_executable\fR) is empty, \fBscado\fR
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computes it automatically when the scado file is saved.
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\fBScado\fR asks for user authentication by PAM to confirm any modification of the scado file.
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There is also a \fITOCTTOU\fR protection at running time: \fDcado -S\fR copies the executable file
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in a safe place, where the user cannot change it, and runs it only if the integrity check on it succeeds.
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The user (or a malicious intruder acting as the user) cannot modify the file after the integrity check has completed
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and before the program is loaded.
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.SH OPTIONS
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.I scado
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accepts the following options:
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.TP
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\fB\-l
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.TQ
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\fB\-\-list
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Display the current scado file. The actual file in the file system is not accessible by unprivileged users, for security reasons.
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.TP
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\fB\-e
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.TQ
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\fB\-\-edit
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Edit the scado file of the current user using the editor specified by either the
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\fBVISUAL\fR or the \fBEDITOR\fR environment variable (checked in that order).
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After you exit from the editor, the modified file will be installed automatically.
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.TP
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\fB\-D
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.TQ
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\fB\-\-delete
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Delete the current user's scado file.
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.TP
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\fB\-u\fR \fIcommand\fR
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.TQ
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\fB\-\-update\fR \fIcommand\fR
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Recompute the hash of the line which starts with \fIcommand\fR.
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.TP
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\fB\-U
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.TQ
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\fB\-\-update-all
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Update all the digest entries.
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.TP
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\fB\-h
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.TQ
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\fB\-\-help
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print a short usage banner and exit.
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.SH EXCEPTIONS FILES EXAMPLES
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.PP
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Allow \fBcado -S\fR to run /bin/ping providing it with the cap_net_raw capability, without any integrity check:
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.RS 4
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/bin/ping : cap_net_raw
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.RE
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.PP
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Allow the activation of ping with cap_net_raw provided it has a specific SHA256 digest
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.RS 4
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/bin/ping : cap_net_raw : dcb237f1cb20ee7b1550900d1b524c554063fd17fc673c56d341736ced6bed4b
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.RE
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.PP
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Compute the SHA256 digest of (the current version of) ping so,
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allow the activation of ping with cap_net_raw provided it has not been modified.
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.RS 4
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/bin/ping : cap_net_raw :
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.RE
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.PP
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If one of the example lines here above has been inserted in the user scado file using
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\fBscado -e\fR, it is possible to execute ping as follows:
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.RS 4
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cado -S cap_net_raw /bin/ping
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.RE
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.SH SEE ALSO
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\fBcado\fR(1),
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\fBcapabilities\fR(7)
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