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

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
aurel32
1 parent 5b257578
Showing 2 changed files with 15 additions and 2 deletions
qemu-doc.texi
vl.c
@@ -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:
@@ -4961,6 +4961,7 @@ static int drive_init(struct drive_opt *arg, int snapshot,
     int bus_id, unit_id;
     int cyls, heads, secs, translation;
     BlockDriverState *bdrv;
+    BlockDriver *drv = NULL;
     int max_devs;
     int index;
     int cache;
@@ -4968,7 +4969,7 @@ static int drive_init(struct drive_opt *arg, int snapshot,
     char *str = arg->opt;
     char *params[] = { "bus", "unit", "if", "index", "cyls", "heads",
                        "secs", "trans", "media", "snapshot", "file",
-                       "cache", NULL };
+                       "cache", "format", NULL };
     if (check_params(buf, sizeof(buf), params, str) < 0) {
          fprintf(stderr, "qemu: unknown parameter '%s' in '%s'\n",
@@ -5136,6 +5137,14 @@ static int drive_init(struct drive_opt *arg, int snapshot,
         }
     }
+    if (get_param_value(buf, sizeof(buf), "format", str)) {
+        drv = bdrv_find_format(buf);
+        if (!drv) {
+            fprintf(stderr, "qemu: '%s' invalid format\n", buf);
+            return -1;
+        }
+    }
+
     if (arg->file == NULL)
         get_param_value(file, sizeof(file), "file", str);
     else
@@ -5238,7 +5247,7 @@ static int drive_init(struct drive_opt *arg, int snapshot,
         bdrv_flags |= BDRV_O_SNAPSHOT;
     if (!cache)
         bdrv_flags |= BDRV_O_DIRECT;
-    if (bdrv_open(bdrv, file, bdrv_flags) < 0 || qemu_key_check(bdrv, file)) {
+    if (bdrv_open2(bdrv, file, bdrv_flags, drv) < 0 || qemu_key_check(bdrv, file)) {
         fprintf(stderr, "qemu: could not open disk image %s\n",
                         file);
         return -1;