Even with USE filecaps enabled several bins are still suid, that seems very strange and makes usage of libcap completely pointless. I did 3 tests: 1) With both suid and filecaps enabled recording iso to DVD-RW works fine. 2) With filecaps enabled and suid disabled recording iso to DVD-RW works fine. chmod 0755 /usr/bin/cdda2wav /usr/bin/cdrecord /usr/bin/readcd /usr/sbin/rscsi 3) With both suid and filecaps disabled recording iso to DVD-RW works fine. At least for linux it seems like suid is pointless in most cases, even when filecaps are disabled user still has rw access to /dev/sr0: # getfacl /dev/sr0 getfacl: Removing leading '/' from absolute path names # file: dev/sr0 # owner: root # group: cdrom user::rw- user:myusername:rw- group::rw- mask::rw- other::--- # grep cdrom /etc/group cdrom:x:19:myusername Portage 2.2.7 (hardened/linux/amd64, gcc-4.7.3, glibc-2.15-r3, 3.11.6-hardened-r1 x86_64) ================================================================= System Settings ================================================================= KiB Mem: 65825872 total, 38640788 free KiB Swap: 0 total, 0 free Timestamp of tree: Sun, 03 Nov 2013 10:45:01 +0000 ld GNU ld (GNU Binutils) 2.23.1 app-shells/bash: 4.2_p45 dev-lang/python: 2.7.5-r3 dev-util/pkgconfig: 0.28 sys-apps/baselayout: 2.2 sys-apps/openrc: 0.11.8 sys-apps/sandbox: 2.6-r1 sys-devel/binutils: 2.23.1 sys-devel/gcc: 4.7.3-r1 sys-devel/gcc-config: 1.7.3 sys-devel/libtool: 2.4.2 sys-devel/make: 3.82-r4 sys-kernel/linux-headers: 3.9 (virtual/os-headers) sys-libs/glibc: 2.15-r3 Repositories: gentoo nikoli ACCEPT_KEYWORDS="amd64" ACCEPT_LICENSE="* -@EULA" CBUILD="x86_64-pc-linux-gnu" CFLAGS="-march=corei7-avx -O2 -pipe" CHOST="x86_64-pc-linux-gnu" CONFIG_PROTECT="/etc /usr/share/config /usr/share/gnupg/qualified.txt /usr/share/themes/oxygen-gtk/gtk-2.0 /usr/share/themes/oxygen-gtk/gtk-3.0" CONFIG_PROTECT_MASK="/etc/ca-certificates.conf /etc/dconf /etc/env.d /etc/fonts/fonts.conf /etc/gconf /etc/gentoo-release /etc/revdep-rebuild /etc/sandbox.d /etc/terminfo" CXXFLAGS="-march=corei7-avx -O2 -pipe" FCFLAGS="-O2 -pipe" FEATURES="assume-digests binpkg-logs cgroup collision-protect config-protect-if-modified distlocks ebuild-locks fixlafiles ipc-sandbox merge-sync network-sandbox news parallel-fetch preserve-libs protect-owned sandbox sfperms strict test unknown-features-warn unmerge-logs unmerge-orphans userfetch userpriv usersandbox usersync xattr" FFLAGS="-O2 -pipe" LANG="en_US.UTF-8" LDFLAGS="-Wl,--hash-style=gnu -Wl,-O1 -Wl,--as-needed" MAKEOPTS="-j9" PORTAGE_CONFIGROOT="/" PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --omit-dir-times --compress --force --whole-file --delete --stats --human-readable --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages" PORTDIR_OVERLAY="/var/lib/layman/nikoli" USE="X a52 aac acl acpi aes-ni alsa amd64 amr audiofile avx bash-completion bzip2 cairo caps cdda cddb cdio cdparanoia cdr celt cli consolekit cracklib crypt css cups cxx dbus djvu dri dts dv dvd dvdr encode exif fat ffmpeg flac fluidsynth fontconfig fortran gd geoip gif gimp gmp gnutls gphoto2 gpm graphviz gsm gstreamer gtk handbook hardened iconv icu id3tag idn ilbc imagemagick imap imlib ios ipod ipv6 jbig jpeg jpeg2k justify kde kipi lame laptop lcms libass libnotify libproxy libsamplerate lm_sensors lzma lzo mac mad matroska mikmod mmx mmxext modplug modules mp3 mp4 mpeg mtp mudflap multilib musepack musicbrainz ncurses networkmanager nls nptl nptlonly ntfs ogg openal openexr opengl openmp opus pam pango pax_kernel pcre pdf pg-intdatetime phonon plasma pm-utils png policykit postscript qt3support qt4 quicktime rar raw readline reiserfs replaygain rtmp sasl scanner semantic-desktop session sid smp sndfile socks5 speex spell sqlite sse sse2 sse3 sse4_1 ssl ssse3 startup-notification svg symlink sysfs taglib theora threads thumbnail tiff truetype tta udev udisks unicode upnp upower usb v4l v4l2 vcd vdpau vorbis vpx wavpack webkit webp wifi wma wmf x264 xattr xcb xcomposite xface xinerama xml xmp xpm xscreensaver xv xvid xz zip zlib" ABI_X86="64" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem bt87x ca0106 cmipci emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel intel8x0 intel8x0m maestro3 trident usb-audio via82xx via82xx-modem ymfpci" APACHE2_MODULES="authn_core authz_core socache_shmcb unixd actions alias auth_basic authn_alias authn_anon authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache cgi cgid dav dav_fs dav_lock deflate dir disk_cache env expires ext_filter file_cache filter headers include info log_config logio mem_cache mime mime_magic negotiation rewrite setenvif speling status unique_id userdir usertrack vhost_alias" CALLIGRA_FEATURES="kexi words flow plan sheets stage tables krita karbon braindump author" CAMERAS="*" COLLECTD_PLUGINS="df interface irq load memory rrdtool swap syslog" ELIBC="glibc" GPSD_PROTOCOLS="ashtech aivdm earthmate evermore fv18 garmin garmintxt gpsclock itrax mtk3301 nmea ntrip navcom oceanserver oldstyle oncore rtcm104v2 rtcm104v3 sirf superstar2 timing tsip tripmate tnt ubx" GRUB_PLATFORMS="efi-64" INPUT_DEVICES="evdev" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LIBREOFFICE_EXTENSIONS="presenter-minimizer" LINGUAS="ru ru_RU en" NGINX_MODULES_HTTP="access auth_basic autoindex fastcgi gzip rewrite" OFFICE_IMPLEMENTATION="libreoffice" PHP_TARGETS="php5-5" PYTHON_SINGLE_TARGET="python2_7" PYTHON_TARGETS="python2_7" QEMU_SOFTMMU_TARGETS="i386 x86_64" QEMU_USER_TARGETS="i386 x86_64" RUBY_TARGETS="ruby20" USERLAND="GNU" VIDEO_CARDS="radeon r600 modesetting vesa" XTABLES_ADDONS="quota2 psd pknock lscan length2 ipv4options ipset ipp2p iface geoip fuzzy condition tee tarpit sysrq steal rawnat logmark ipmark dhcpmac delude chaos account" Unset: CPPFLAGS, CTARGET, EMERGE_DEFAULT_OPTS, LC_ALL, PORTAGE_BUNZIP2_COMMAND, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS, SYNC, USE_PYTHON ================================================================= Package Settings ================================================================= app-cdr/cdrtools-3.01_alpha17 was built with the following: USE="acl filecaps nls unicode" CFLAGS="-march=corei7-avx -O2 -pipe -finput-charset=ISO-8859-1 -fexec-charset=UTF-8" CXXFLAGS="-march=corei7-avx -O2 -pipe -finput-charset=ISO-8859-1 -fexec-charset=UTF-8"
Also i think USE filecaps should be disabled by default or even removed: it turns 0660 permission for /dev/sr0 into 0666.
The permissions for /dev/sr0 are unrelated to cdrtools filecaps. Also note that libscg tries to avoid /dev/srx because there is a better driver in /dev/sg* If someone believes that cdrtools work correctly with less than the documented additional privileges,he did not run the right tests. Just because things seem to work under certain conditions, this does neither mean that it did work the best way nor that it will work under other conditions. cdrecord/readcd/cdda2wav either need to be installed suid root or with the documented filecaps.
(In reply to Nikoli from comment #0) > Even with USE filecaps enabled several bins are still suid, that seems very > strange and makes usage of libcap completely pointless. Not here. Which several bins? Only rscsi is installed suid root under /usr/sbin here. Filecaps are only applied to cdrecord, cdda2wav and readcd. > I did 3 tests: > 1) With both suid and filecaps enabled recording iso to DVD-RW works fine. This should never be the case. > 2) With filecaps enabled and suid disabled recording iso to DVD-RW works > fine. Which is to be expected. The same goes for disabling filecaps to get the binaries as suid root. > chmod 0755 /usr/bin/cdda2wav /usr/bin/cdrecord /usr/bin/readcd > /usr/sbin/rscsi > 3) With both suid and filecaps disabled recording iso to DVD-RW works fine. Does not work here. Example output from cdrecord: cdrecord: Operation not permitted. Warning: Cannot raise RLIMIT_MEMLOCK limits. cdrecord: Cannot allocate memory. WARNING: Cannot do mlockall(2). cdrecord: WARNING: This causes a high risk for buffer underruns. cdrecord: Operation not permitted. WARNING: Cannot set RR-scheduler. cdrecord: Permission denied. WARNING: Cannot set priority using setpriority(). cdrecord: WARNING: This causes a high risk for buffer underruns. cdrecord: Insufficient 'file read' privileges. You will not be able to open all needed devices. cdrecord: Insufficient 'file write' privileges. You will not be able to open all needed devices. cdrecord: Insufficient 'device' privileges. You may not be able to send all needed SCSI commands, this my cause various unexplainable problems. cdrecord: Insufficient 'memlock' privileges. You may get buffer underruns. cdrecord: Insufficient 'priocntl' privileges. You may get buffer underruns. cdrecord: Insufficient 'network' privileges. You will not be able to do remote SCSI. The filecaps use flag enables the required capabilities and does not install them as suid root. Disabling the use flag installs them suid root. Maybe there is an issue with the fcaps eclass.
(In reply to Nikoli from comment #1) > Also i think USE filecaps should be disabled by default or even removed: it > turns 0660 permission for /dev/sr0 into 0666. Not here! Also I don't think cdrtools mess with /dev/sr*.
> The permissions for /dev/sr0 are unrelated to cdrtools filecaps. Did not know. > Also note that libscg tries to avoid /dev/srx because there is a better driver in /dev/sg* sg module is installed to /lib/modules/, but udev does not autoload it, so there were no /dev/sg* until i did 'modprobe sg'. Is it udev bug? Also where can i read about why /dev/sg* is better for cdrtools? > cdrecord/readcd/cdda2wav either need to be installed suid root or with the documented filecaps. What problems may happen when both suid and filecaps are disabled? > Not here. Which several bins? Only rscsi is installed suid root under /usr/sbin here. Filecaps are only applied to cdrecord, cdda2wav and readcd. Did 'emerge --sync; emerge -1vba app-cdr/cdrtools'. Now only /usr/sbin/rscsi is 4711, but /usr/bin/{cdda2wav,cdrecord,readcd} are 0711. > > 3) With both suid and filecaps disabled recording iso to DVD-RW works fine. > Does not work here. Example output from cdrecord: What command and device (sr or sg) you were using? I used k3b for testing, will try cli. > Not here! Also I don't think cdrtools mess with /dev/sr*. Then how should permissions for /dev/sg* /dev/sr* and user presence in 'cdrom' group affect usage of cdrtools?
(In reply to Nikoli from comment #5) > > Also note that libscg tries to avoid /dev/srx because there is a better > driver in /dev/sg* > > sg module is installed to /lib/modules/, but udev does not autoload it, so > there were no /dev/sg* until i did 'modprobe sg'. Is it udev bug? Also where > can i read about why /dev/sg* is better for cdrtools? I don't know. Maybe it is better to not make this driver a module. Do you use dev=/dev/sr0? You should use the scsibus instead. You will find the bus for your drive with cdrecord -scanbus > > cdrecord/readcd/cdda2wav either need to be installed suid root or with > the documented filecaps. > > What problems may happen when both suid and filecaps are disabled? No problems but you can not use cdrtools as a normal user. > > Not here. Which several bins? Only rscsi is installed suid root under /usr/sbin here. Filecaps are only applied to cdrecord, cdda2wav and readcd. > > Did 'emerge --sync; emerge -1vba app-cdr/cdrtools'. Now only /usr/sbin/rscsi > is 4711, but /usr/bin/{cdda2wav,cdrecord,readcd} are 0711. This is how it should be with filecaps enabled. You can use getcap on the binaries to check the capabilities. > > > 3) With both suid and filecaps disabled recording iso to DVD-RW works fine. > > > Does not work here. Example output from cdrecord: > > What command and device (sr or sg) you were using? I used k3b for testing, > will try cli. cdrecord dev=x,x,x iso I think cdrecord tries to use the sg driver first maybe it falls back to sr if this fails. > > Not here! Also I don't think cdrtools mess with /dev/sr*. > > Then how should permissions for /dev/sg* /dev/sr* and user presence in > 'cdrom' group affect usage of cdrtools? I don't understand your question. The required permissions are defined in the capabilities. If libcap is installed, the kernel and the filesystem supports them everything should be fine. When do you think the cdrecord changes the permissions of /dev/sr0? Are they changed after you use cdrecord?
(In reply to Nikoli from comment #5) > > The permissions for /dev/sr0 are unrelated to cdrtools filecaps. > > Did not know. Adding file permissions to everyone and removing restrictions in the linux kernel is a security bug that was introduced in early 2004. Instead of removing an introduced security issue, Torvalds decided to add other problems that allow to partialy hide the problems from the first bug. The current situation is higly copmplex and makes it hard to understand the efects. BTW: the original security issue has been introduced by a driver newcomer (Douglas Gilbert) who misses the skills to know that the original versions of the sg driver on Linux worked based on read(2)/write(2) calls and that thus the sg permissions 644 did only allow root to send SCSI commands. He added an ioctl() to replace the previous read/write based interface and a driver professional would have added a check to the ioctl code that verifies that the driver was opened R/W... > > Also note that libscg tries to avoid /dev/srx because there is a better > driver in /dev/sg* > > sg module is installed to /lib/modules/, but udev does not autoload it, so > there were no /dev/sg* until i did 'modprobe sg'. Is it udev bug? Also where > can i read about why /dev/sg* is better for cdrtools? The last time, I did run scgcheck in order to check the correctness of the SCSI transport system, /dev/sg* was the best on Linux. I remember e.g. problems with reliably getting more DMA space. There is also a repeatedly hitting trap that is caused by the fact that the SCSI implementation in the linux kernel is hosed: e.g. the internal representation of the SCSI status code is shifted by one in the kernel and few kackers are skilled enough to know this. As a result, every other year, someone introduces a related bug in the needlessly replicated code that exists besides /dev/sg. Cdrtools can only work correctly, when it knows the exact cause for a "failed" SCSI command as the SCSI protocol depends the related error codes. > > cdrecord/readcd/cdda2wav either need to be installed suid root or with > the documented filecaps. > > What problems may happen when both suid and filecaps are disabled? I recommend to read the long version in various places on the net. I did repeat this sooooooooo many times before. Note that the claim that there is no problem without having the apropriate privileges is a fairy tale spread by the OSS hostile people from Debian as part of their crusade against the cdrtools. When there recently was a reply at all on the countless problem reports for their so called "fork", they recommended to rerun the command with root privileges ;-) well these prople don't have fine grained priv support. > > Not here. Which several bins? Only rscsi is installed suid root under /usr/sbin here. Filecaps are only applied to cdrecord, cdda2wav and readcd. > > Did 'emerge --sync; emerge -1vba app-cdr/cdrtools'. Now only /usr/sbin/rscsi > is 4711, but /usr/bin/{cdda2wav,cdrecord,readcd} are 0711. OK, if there is really a need, I could create a fine grained enabled version of rscsi. > Then how should permissions for /dev/sg* /dev/sr* and user presence in > 'cdrom' group affect usage of cdrtools? If the commands are run with apropriate privs, the permissions do not affect the behavior.
(In reply to joerg.schilling from comment #7) > > > > Not here. Which several bins? Only rscsi is installed suid root under /usr/sbin here. Filecaps are only applied to cdrecord, cdda2wav and readcd. > > > > Did 'emerge --sync; emerge -1vba app-cdr/cdrtools'. Now only /usr/sbin/rscsi > > is 4711, but /usr/bin/{cdda2wav,cdrecord,readcd} are 0711. > > OK, if there is really a need, I could create a fine grained enabled > version of rscsi. > Personally I do not use rscsi, but having rscsi using capabilities instead of being suid root would be beneficial. Also people could get confused if they enable file capabilities but still get rscsi with suid root permissions.
(In reply to Daniel Pielmeier from comment #6) > (In reply to Nikoli from comment #5) > cdrecord dev=x,x,x iso > I think cdrecord tries to use the sg driver first maybe it falls back to sr > if this fails. > Correct, libscg is a generic SCSI transport library and it first tries to use the best choice (linux offers more than one driver for a specific hardware) first. If there is no luck, it tries lessoptimal drivers. If the /dev/sg* is not loaded by default, this is a bug.
I am closing this bug as I think there is nothing related to cdrtools here. If there are any issues with module loading or other problems a new bug should be opened. Also if it is desired to make rscsi use fine grained privileges there should be a separate bug.
