mirror of https://github.com/rd235/cado
195 lines
6.4 KiB
Plaintext
195 lines
6.4 KiB
Plaintext
introducing CADO: Capability DO.
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Cado permits to delegate capabilities to users.
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Cado is a capability based sudo. Sudo allows authorized users to run programs
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as root (or as another user), cado allows authorized users to run programs with
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specific (ambient) capabilities.
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Cado is more selective than sudo, users can be authorized to have only specific capabilities (and not others).
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INSTALL:
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get the source code, from the root of the source tree run:
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$ autoreconf -if
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$ ./configure
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$ make
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$ sudo make install
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It installs two programs in /usr/local/bin: cado and caprint.
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If you want to install the programs in /usr/bin run "./configure --prefix=/usr" instead of "./configure".
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Cado needs a configuration file: /etc/cado.conf with the following syntax:
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* lines beginning with # are comments
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* all the other lines have two fields separated by :, the first field is a capability or a list of
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capabilities, the second field is a list of users or groups (group names have @ as a prefix).
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Capabilities can be written with or without the cap_ prefix (net_admin means cap_net_admin).
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Example of /etc/cado.conf file:
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---------------------------------------------
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# Capability Ambient DO configuration file
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# cado.conf
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net_admin: @netadmin,renzo
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cap_kill: renzo
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--------------------------------------------
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The file above allows the user renzo and all the members of the group named netadmin to run programs
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neeeding the cap_net_admin capability.
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The user renzo can also run programs requiring cap_kill.
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The file /etc/cado.conf can be owned by root and have no rw permission for users.
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It is also possible to use lists of capabilities:
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setgid,setuid: giovanni
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or exadecimal masks:
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c0: giovanni,@idgroup
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$ ls -l /etc/cado.conf
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-rw------- 1 root root 100 Jun 19 17:11 /etc/cado.conf
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IMPORTANT.
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Cado has been designed to work using the minimum set of capability required for its services.
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(following the principle of least privilege).
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Cado itself is not a seuid executable, it uses the capability mechanism and it has an options to
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set its own capabilities. So after each change in the /etc/cado.conf, the capability set should be
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recomputed using the following command:
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$ sudo cado -s
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or
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$ sudo cado -sv
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(this latter command is verbose and shows the set of capabilties assigned to the capo executable file).
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using the example configuration file above, capo would be assigned the following capabilities:
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$ sudo cado -sv
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Capability needed by cado:
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2 0000000000000004 cap_dac_read_search
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5 0000000000000020 cap_kill
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12 0000000000001000 cap_net_admin
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0000000000001024
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$ /sbin/getcap /usr/local/bin/cado
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/usr/local/bin/cado = cap_dac_read_search,cap_kill,cap_net_admin+p
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-----------------------------------------------------------------
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The syntax of cado is simple:
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$ cado [options] set_of_capabilities command [args]
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for example if the user renzo wants to run a shell having the cap_net_admin capability enabled he can type
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the following command:
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$ cado net_admin bash
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Password:
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$
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the user will be requested to authenticate himself. If the user has the right to enable cap_net_admin (from the
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cado.conf configuration file) and he typed in the correct password, cado starts a new shell with the requested
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capability enabled.
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It is possible define the set_of_capabilities using a list of capabilities (with or without the cap_prefix)
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or exadecimal masks.
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In the new shell the user can do all the operations permitted by the enabled capabilities,
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in this case, for example, he will be allowed to change the networking configuration, add tuntap
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interfaces and so on.
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It is possible to show the ambient capability set of a program by reading the /proc/####/status file:
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e.g.:
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$ grep CapAmb /proc/$$/status
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CapAmb: 0000000000001000
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(cap_net_admin is the capability #12, the mask is 0x1000, i.e. 1ULL << 12)
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-----------------------------------------------------------------
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caprint is a simple program which shows the ambient capabilities of a running program.
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(a pid of a running process can be specified as an optional parameter, otherwise it shows the capabilities
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of caprint itself)
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$ caprint
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cap_net_admin
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$ caprint -l
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12 0000000000001000 cap_net_admin
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There is an option -p that has been designed to add the current set of ambient capabilities to the shell prompt,
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so it is easier for the user to recognize when a shell has some "extra power", so to avoid errors.
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In .bashrc or .bash_profile (or in their system-side counterparts in /etc) it is possible to set rules like
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the followings:
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-----------
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if which caprint >&/dev/null ; then
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ambient=$(caprint -p)
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fi
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PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$$ambient '
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-----------
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The prompt becomes something like:
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renzo@host:~$net_admin#
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-------------------------------------------------------------------
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Some secondary features:
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The -v feature shows the set of available capabilities:
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$ cado -v
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Allowed ambient capabilities:
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5 0000000000000020 cap_kill
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12 0000000000001000 cap_net_admin
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0000000000001020
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$ cado -v net_admin,kill bash
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Allowed ambient capabilities:
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5 0000000000000020 cap_kill
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12 0000000000001000 cap_net_admin
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0000000000001020
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Requested ambient capabilities:
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5 0000000000000020 cap_kill
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12 0000000000001000 cap_net_admin
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0000000000001020
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Password:
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It is useful to show which capability/ies cannot be granted:
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$ cado net_admin,kill,setuid bash
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cado: Permission denied
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$ cado -v net_admin,kill,setuid bash
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Allowed ambient capabilities:
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5 0000000000000020 cap_kill
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12 0000000000001000 cap_net_admin
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0000000000001020
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Requested ambient capabilities:
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5 0000000000000020 cap_kill
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7 0000000000000080 cap_setuid
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12 0000000000001000 cap_net_admin
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00000000000010a0
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Unavailable ambient capabilities:
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7 0000000000000080 cap_setuid
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cado: Permission denied
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It is possible to enable only the capability allowed by setting the -q option
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(with or without -v). Using -q cado does not fail.
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$ cado -qv net_admin,kill,setuid bash
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Allowed ambient capabilities:
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5 0000000000000020 cap_kill
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12 0000000000001000 cap_net_admin
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0000000000001020
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Requested ambient capabilities:
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5 0000000000000020 cap_kill
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7 0000000000000080 cap_setuid
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12 0000000000001000 cap_net_admin
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00000000000010a0
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Unavailable ambient capabilities:
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7 0000000000000080 cap_setuid
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Password:
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Granted ambient capabilities:
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5 0000000000000020 cap_kill
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12 0000000000001000 cap_net_admin
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0000000000001020
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renzo@eipi:~/tests/cado/pre$kill,net_admin#
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