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Re: [Qemu-devel] [Bug 807893] Re: qemu privilege escalation
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [Bug 807893] Re: qemu privilege escalation |
Date: |
Thu, 14 Jul 2011 11:19:44 -0000 |
On Thu, Jul 14, 2011 at 11:37 AM, Andrew Griffiths
<address@hidden> wrote:
> Regarding the threads having different privilege level, I have isolated
> that to being related to my grsecurity configuration (more specifically,
> chroot_findtask will block it).
>
> While it's still an issue on older glibc where the setuid/setgid code
> does not enforce it across all threads, it may not be high priority
> since fixing it would be a lot more effort.
Wow, just learnt something new that glibc does behind our backs :). I
see it uses SIGRTMIN+1 to signal threads and get them to do the set*id
system calls.
I'm glad it does this because although most QEMU threads should be
started after command-line parsing, I can think of instances where we
might start a thread before -runas is completed.
Stefan
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https://bugs.launchpad.net/bugs/807893
Title:
qemu privilege escalation
Status in QEMU:
Confirmed
Bug description:
If qemu is started as root, with -runas, the extra groups is not
dropped correctly
/proc/`pidof qemu`/status
..
Uid: 100 100 100 100
Gid: 100 100 100 100
FDSize: 32
Groups: 0 1 2 3 4 6 10 11 26 27
...
The fix is to add initgroups() or setgroups(1, [gid]) where
appropriate to os-posix.c.
The extra gid's allow read or write access to other files (such as
/dev etc).
Emulating the qemu code:
# python
...
>>> import os
>>> os.setgid(100)
>>> os.setuid(100)
>>> os.execve("/bin/sh", [ "/bin/sh" ], os.environ)
sh-4.1$ xxd /dev/sda | head -n2
0000000: eb48 9000 0000 0000 0000 0000 0000 0000 .H..............
0000010: 0000 0000 0000 0000 0000 0000 0000 0000 ................
sh-4.1$ ls -l /dev/sda
brw-rw---- 1 root disk 8, 0 Jul 8 11:54 /dev/sda
sh-4.1$ id
uid=100(qemu00) gid=100(users)
groups=100(users),0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy),26(tape),27(video)
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