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# Using File Capabilities Instead Of Setuid

From ArchWiki

The intention of this article is to remove the setuid attribute in the binaries that require certain root-privileges. In this way, it eliminates the need for "all or nothing", using a fine grained control with POSIX 1003.1e capabilities.

Use with caution, some programs do not know about file capabilities. It apparently works correctly, but have some unexpected side effects (see for example #util-linux-ng)

## Prerequisites

You need libcap, for setting file capabalities that are extended attributes, with the utility setcap.

    # pacman -S libcap

## Setuid-root files by package

### coreutils

Note: Warning: Do not use it, because su will return incorrect password.

    # chmod u-s /bin/su
    # setcap cap_setgid,cap_setuid+ep /bin/su

### dcron

    # chmod u-s /usr/bin/crontab
    # setcap cap_dac_override,cap_setgid+ep /usr/bin/crontab

### inetutils

    # chmod u-s /usr/bin/rsh
    # setcap cap_net_bind_service+ep /usr/bin/rsh

    # chmod u-s /usr/bin/rcp
    # setcap cap_net_bind_service+ep /usr/bin/rcp

    # chmod u-s /usr/bin/rlogin
    # setcap cap_net_bind_service+ep /usr/bin/rlogin

### iputils

    # chmod u-s /bin/ping
    # setcap cap_net_raw+ep /bin/ping

    # chmod u-s /bin/ping6
    # setcap cap_net_raw+ep /bin/ping6

    # chmod u-s /bin/traceroute
    # setcap cap_net_raw+ep /bin/traceroute

    # chmod u-s /bin/traceroute6
    # setcap cap_net_raw+ep /bin/traceroute6

### pam

    # chmod u-s /sbin/unix_chkpwd
    # setcap cap_dac_read_search+ep /sbin/unix_chkpwd

### pmount

Does not work without setuid.

### pulseaudio

    # chmod u-s /usr/lib/pulse/proximity-helper
    # setcap cap_net_raw+ep /usr/lib/pulse/proximity-helper

### screen

Needs setuid for multiuser sessions, but if you don't need that feature, you can safely turn off setuid.

### shadow

    # chmod u-s /usr/bin/chage
    # setcap cap_dac_read_search+ep /usr/bin/chage

    # chmod u-s /usr/bin/chfn
    # setcap cap_chown,cap_setuid+ep /usr/bin/chfn

    # chmod u-s /usr/bin/chsh
    # setcap cap_chown,cap_setuid+ep /usr/bin/chsh

    # chmod u-s /usr/bin/expiry
    # setcap cap_dac_override,cap_setgid+ep /usr/bin/expiry

    # chmod u-s /usr/bin/gpasswd
    # setcap cap_chown,cap_dac_override,cap_setuid+ep /usr/bin/gpasswd

    # chmod u-s /usr/bin/newgrp
    # setcap cap_dac_override,cap_setgid+ep /usr/bin/newgrp

    # chmod u-s /usr/bin/passwd
    # setcap cap_chown,cap_dac_override,cap_fowner+ep /usr/bin/passwd

### sudo

Sudo does not work without setuid.

### util-linux-ng

Note: Warning: Do not use it, because mount and umount can not do some checks, then users can mount/umount filesystems that do not have permission.

    # chmod u-s /bin/mount
    # setcap cap_dac_override,cap_sys_admin+ep /bin/mount

    # chmod u-s /bin/umount
    # setcap cap_dac_override,cap_sys_admin+ep /bin/umount

### xorg-xserver

    # chmod u-s /usr/bin/Xorg
    # setcap cap_chown,cap_dac_override,cap_sys_rawio,cap_sys_admin+ep /usr/bin/Xorg

## Other programs that benefit from capabilities

The following packages do not have files with the setuid attribute but require root privileges to work. By enabling some capabilities, regular users can use the program without privilege elevation.

### beep

    # setcap cap_dac_override,cap_sys_tty_config+ep /usr/bin/beep

### chvt

    # setcap cap_dac_read_search,cap_sys_tty_config+ep /usr/bin/chvt

### iftop

    # setcap cap_net_raw+ep /usr/sbin/iftop

### mii-tool

    # setcap cap_net_admin+ep /sbin/mii-tool

## Useful commands

Find setuid-root files

    $ find /usr/bin /usr/lib -perm /4000 -user root

Find setgid-root files

    $ find /usr/bin /usr/lib -perm /2000 -group root

## Additional Resources

- Man Page capabilities(7) setcap(8) getcap(8)

Retrieved from "https://wiki.archlinux.org/index.php?title=Using_File_Capabilities_Instead_Of_Setuid&oldid=266677"
Category:

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