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Date: Fri, 03 Jan 2014 21:24:57 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] seccomp: add mkdir() and fchmod() to the
	whitelist
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To: Paul Moore <pmoore@redhat.com>
Cc: qemu-devel@nongnu.org, otubo@linux.vnet.ibm.com

Il 03/01/2014 20:58, Paul Moore ha scritto:
> The PulseAudio library attempts to do a mkdir(2) and fchmod(2) on
> "/run/user/<UID>/pulse" which is currently blocked by the syscall
> filter; this patch adds the two missing syscalls to the whitelist.
> You can reproduce this problem with the following command:
> 
>  # qemu -monitor stdio -device intel-hda -device hda-duplex
> 
> If watched under strace the following syscalls are shown:
> 
>  mkdir("/run/user/0/pulse", 0700)
>  fchmod(11, 0700) [NOTE: 11 is the fd for /run/user/0/pulse]

Can fchmod be exploited to violate the sandbox (e.g. to let data escape
from a VM that ought not to have any way to communicate with the outside
world)?

Paolo