Date: Wed, 18 Sep 2013 14:15:49 +0200 From: Sebastian Krahmer <krahmer@...e.de> To: oss-security@...ts.openwall.com Subject: Fwd: [vs-plain] polkit races Hi list As required by distros list policy, I forward this to oss-security. The initial CRD was Sept 11th, but it was shifted to today as there were so many packages to be fixed. regards Sebastian ----- Forwarded message from Sebastian Krahmer <krahmer@...e.de> ----- From: Sebastian Krahmer <krahmer@...e.de> To: distros@...openwall.org Subject: [vs-plain] polkit races Date: Wed, 28 Aug 2013 10:17:37 +0200 Hi The polkit unix-process subject for authorization is racy. It depended on the (PID, startup_time) pair to be passed to polkit which then used /proc/PID/status to find out the UID the process belongs to. Meanwhile the process could have started a suid or pkexec process, changing the euid and/or uid at will. The startup_time does not protect here, as its not changed across an execve(). Using /proc/PID/loginuid wont work either, as one could abuse fork-spawning processes such as sshd, apache etc. to re-use recently freed process slots, faking the loginuid. startup_time would theoretically help here, yet as its not atomically passed along the message which is subject to polkit authorization, the privileged process needs to learn it by looking up /proc/PID/, which is racy again. Therefore the only thing that could be used is the UID that is passed atomically in the peer cred struct when receiving the message in question. The whole thing needs fixing in polkit, to deprecate PID authorization as well as several core packages to make use of the new API, or use systembus authorization. After discussing with upstream, Colin Walters made this private git of patches available: http://people.freedesktop.org/~walters/secret/38b060a751ac96384cd9327eb1b1e36a21fdb71114be07434c0cc7bf63f6e1da274edebfe76f65fbd51ad2f14898b95b/ Feel free to suggest improvements if necessary. As required by list policy, I request a CRD of Sept 11th. We also need CVE's assigned. A PoC with example client/server which demonstrates the race can be found here (it basically simulates libvirtd's way of checking): http://suse.de/~krahmer/priv/polkit-race.tgz Sebastian -- ~ perl self.pl ~ $_='print"\$_=\47$_\47;eval"';eval ~ krahmer@...e.de - SuSE Security Team ----- End forwarded message ----- -- ~ perl self.pl ~ $_='print"\$_=\47$_\47;eval"';eval ~ krahmer@...e.de - SuSE Security Team
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