add format= to drive options (CVE-2008-2004)

It is possible for a guest with a raw formatted disk image to write a
header to that disk image describing another format (such as qcow2).
Stopping and subsequent restart of the guest will cause qemu to detect
that format, and could allow the guest to read any host file if qemu is
sufficiently privileged (typical in virt environments).

The patch defaults to existing behaviour (probing based on file contents),
so it still requires the mgmt app (e.g. libvirt xml) to pass a new
"format=raw" parameter for raw disk images.

Originally noted by Avi Kivity, patch from Chris Wright.


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@4277 c046a42c-6fe2-441c-8c8c-71466251a162

1 files changed, 4 insertions, 0 deletions

diff --git a/qemu-doc.texi b/qemu-doc.texi
index 45c89ce26..1f409f47f 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -261,6 +261,10 @@ These options have the same definition as they have in @option{-hdachs}.
 @var{snapshot} is "on" or "off" and allows to enable snapshot for given drive (see @option{-snapshot}).
 @item cache=@var{cache}
 @var{cache} is "on" or "off" and allows to disable host cache to access data.
+@item format=@var{format}
+Specify which disk @var{format} will be used rather than detecting
+the format.  Can be used to specifiy format=raw to avoid interpreting
+an untrusted format header.
 @end table
 
 Instead of @option{-cdrom} you can use: