[gentoo-user] Cdrtools installation without suid root
Hi all, since Linux-2.6.24, fcaps support is part of the vanilla kernel. If you also add libcap user and developer support and the commands getcap and setcap, you will be able to install working versions for: cdrecord, cdda2wav, readcd without making them suid-root. This works with cdrtools-3.01a14 or later. Check ftp://ftp.berlios.de/pub/cdrecord/alpha/ for the sources. Happy hacking! Jörg -- EMail:jo...@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin j...@cs.tu-berlin.de(uni) joerg.schill...@fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/ URL: http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily
Re: [gentoo-user] Cdrtools installation without suid root
On Fri, Apr 26, 2013 at 06:18:13PM +0200, Joerg Schilling wrote: Hi all, since Linux-2.6.24, fcaps support is part of the vanilla kernel. If you also add libcap user and developer support and the commands getcap and setcap, you will be able to install working versions for: cdrecord, cdda2wav, readcd without making them suid-root. This works with cdrtools-3.01a14 or later. Check ftp://ftp.berlios.de/pub/cdrecord/alpha/ for the sources. Happy hacking! Jörg Thanks, Jorg -- Happy Penguin Computers ') 126 Fenco Drive ( \ Tupelo, MS 38801 ^^ supp...@happypenguincomputers.com 662-269-2706 662-205-6424 http://happypenguincomputers.com/ A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail? Don't top-post: http://en.wikipedia.org/wiki/Top_post#Top-posting
Re: [gentoo-user] Cdrtools installation without suid root
Joerg Schilling schrieb am 26.04.2013 18:18: Hi all, since Linux-2.6.24, fcaps support is part of the vanilla kernel. If you also add libcap user and developer support and the commands getcap and setcap, you will be able to install working versions for: cdrecord, cdda2wav, readcd without making them suid-root. This works with cdrtools-3.01a14 or later. Check ftp://ftp.berlios.de/pub/cdrecord/alpha/ for the sources. Happy hacking! Jörg Thanks Jörg, I have read the release notes for alpha14 and prepared an ebuild which automatically applies the required capabilities if the filecaps USE flag is set. Is there any chance to make this a configurable option, so it is possible to disable file capabilities even if libcap is installed? -- Regards Daniel Pielmeier signature.asc Description: OpenPGP digital signature
Re: [gentoo-user] Cdrtools installation without suid root
Daniel Pielmeier bil...@gentoo.org wrote: without making them suid-root. This works with cdrtools-3.01a14 or later. Check ftp://ftp.berlios.de/pub/cdrecord/alpha/ Thanks Jörg, I have read the release notes for alpha14 and prepared an ebuild which automatically applies the required capabilities if the filecaps USE flag is set. Is there any chance to make this a configurable option, so it is possible to disable file capabilities even if libcap is installed? If you install cdrecord/cdda2wav/readcd suid-root instead of applying the facps privileges, cdrtools will automatically behave as before. Is this sufficient? Note that if cdrtools was compiled on a machine with libcap installed, it needs libcap to run. Jörg -- EMail:jo...@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin j...@cs.tu-berlin.de(uni) joerg.schill...@fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/ URL: http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily
Re: [gentoo-user] Cdrtools installation without suid root
Joerg Schilling schrieb am 26.04.2013 19:07: Daniel Pielmeier bil...@gentoo.org wrote: without making them suid-root. This works with cdrtools-3.01a14 or later. Check ftp://ftp.berlios.de/pub/cdrecord/alpha/ Thanks Jörg, I have read the release notes for alpha14 and prepared an ebuild which automatically applies the required capabilities if the filecaps USE flag is set. Is there any chance to make this a configurable option, so it is possible to disable file capabilities even if libcap is installed? If you install cdrecord/cdda2wav/readcd suid-root instead of applying the facps privileges, cdrtools will automatically behave as before. Is this sufficient? Note that if cdrtools was compiled on a machine with libcap installed, it needs libcap to run. Jörg Actually it is the linkage against libcap what I am concerned of. Imagine the following scenario. Libcap is not present on the system. Then package X which requires libcap is installed and the package manager who knows this installs libcap as a dependency. Then package Y is installed which unconditionally links against libcap. The package manager is unaware of this and does not know about the dependency. Now package X is uninstalled and the package manager removes libcap because he thinks nothing on the system needs it anymore. Now package Y will stop working because libcap is not there anymore. If it is possible to conditionally link against libcap such issues could be avoided. Libcap will not be uninstalled if the dependency is known. Additionally it is possible to have libcap installed and not link cdrtools against it. -- Regards Daniel signature.asc Description: OpenPGP digital signature
Re: [gentoo-user] Cdrtools installation without suid root
Daniel Pielmeier bil...@gentoo.org wrote: Actually it is the linkage against libcap what I am concerned of. This is what I call a security risk with the current concepts of some linux systems. See Announcement file for more Imagine the following scenario. Libcap is not present on the system. Then package X which requires libcap is installed and the package manager who knows this installs libcap as a dependency. Then package Y is installed which unconditionally links against libcap. The package manager is unaware of this and does not know about the dependency. Now package X is uninstalled and the package manager removes libcap because he thinks nothing on the system needs it anymore. Now package Y will stop working because libcap is not there anymore. If it is possible to conditionally link against libcap such issues could be avoided. Libcap will not be uninstalled if the dependency is known. Additionally it is possible to have libcap installed and not link cdrtools against it. On Solaris, you cannot remove files that are part of the basic kernel features. Privileges on Solaris are a basic kernel feature and part of the basic security concept, so you cannot remove this on most Linux distros, it seems that you can. I am concerned about a different scenario: Imagine, you compile cdrtools without libcap and later install the support for the OS. Now you decide to use setcap to make cdrecord work. Cdrecord will really work this way, but you opened a security hole as this cdrecord now is not privileges aware and thus cannot even detect that it is running with more than basic privileges. Such a cdrecord installation will happyly write any local file for any local user to CD. Jörg -- EMail:jo...@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin j...@cs.tu-berlin.de(uni) joerg.schill...@fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/ URL: http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily
Re: [gentoo-user] Cdrtools installation without suid root
Joerg Schilling schrieb am 26.04.2013 20:31: Daniel Pielmeier bil...@gentoo.org wrote: Actually it is the linkage against libcap what I am concerned of. This is what I call a security risk with the current concepts of some linux systems. See Announcement file for more Imagine the following scenario. Libcap is not present on the system. Then package X which requires libcap is installed and the package manager who knows this installs libcap as a dependency. Then package Y is installed which unconditionally links against libcap. The package manager is unaware of this and does not know about the dependency. Now package X is uninstalled and the package manager removes libcap because he thinks nothing on the system needs it anymore. Now package Y will stop working because libcap is not there anymore. If it is possible to conditionally link against libcap such issues could be avoided. Libcap will not be uninstalled if the dependency is known. Additionally it is possible to have libcap installed and not link cdrtools against it. On Solaris, you cannot remove files that are part of the basic kernel features. Privileges on Solaris are a basic kernel feature and part of the basic security concept, so you cannot remove this on most Linux distros, it seems that you can. I am concerned about a different scenario: Imagine, you compile cdrtools without libcap and later install the support for the OS. Now you decide to use setcap to make cdrecord work. Cdrecord will really work this way, but you opened a security hole as this cdrecord now is not privileges aware and thus cannot even detect that it is running with more than basic privileges. Such a cdrecord installation will happyly write any local file for any local user to CD. Jörg If you add an option to make conditional linkage against libcap possible there are only two possible scenarios. cdrtools links against libcap and the capabilities are set or it doesn't link against libcap and cdrtools are installed suid root without capabilities. Everything is done in the ebuild and the user does not need to mess with setcap. It is controlled by the package manager and the linkage and capability setting are tied together at installation time. Just adding an option similar to the one for the ACLs would make my live a lot easier. Just enable it by default and make it possible to switch it off. -- Regards Daniel Pielmeier signature.asc Description: OpenPGP digital signature
Re: [gentoo-user] Cdrtools installation without suid root
Daniel Pielmeier bil...@gentoo.org wrote: I am concerned about a different scenario: Imagine, you compile cdrtools without libcap and later install the support for the OS. Now you decide to use setcap to make cdrecord work. Cdrecord will really work this way, but you opened a security hole as this cdrecord now is not privileges aware and thus cannot even detect that it is running with more than basic privileges. Such a cdrecord installation will happyly write any local file for any local user to CD. Jörg If you add an option to make conditional linkage against libcap possible there are only two possible scenarios. cdrtools links against libcap and the capabilities are set or it doesn't link against libcap and cdrtools are installed suid root without capabilities. Everything is done in the ebuild and the user does not need to mess with setcap. It is controlled by the package manager and the linkage and capability setting are tied together at installation time. Just adding an option similar to the one for the ACLs would make my live a lot easier. Just enable it by default and make it possible to switch it off. I am not shure whether there is a missunderstanding. You could have an installation without libcap and without setcap/getcap where cdrecord still has active file capabilities. Nobody could check why, but cdrecord would be able to write any local file to CD on such a system. The only problem I see is that you are able to remove important software on a Linux installation while the kernel still supports the feature by default. Jörg -- EMail:jo...@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin j...@cs.tu-berlin.de(uni) joerg.schill...@fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/ URL: http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily
