Configurable block format whitelist

We have code for a quite a few block formats.  While I trust that all
of these formats are useful at least for some people in some
circumstances, some of them are of a kind that friends don't let
friends use in production.

This patch provides an optional block format whitelist, default off.
If a whitelist is configured with --block-drv-whitelist, QEMU proper
can use only whitelisted formats.  Other programs, like qemu-img, are
not affected.

Drivers for formats off the whitelist still participate in format
probing, to ensure all programs probe exactly the same.  Without that,
QEMU proper would be prone to treat images with a format off the
whitelist as raw when the image's format is probed.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

7 files changed, 58 insertions, 5 deletions

diff --git a/block.c b/block.c
index 05c8311..1e49bc0 100644
--- a/block.c
+++ b/block.c
@@ -61,6 +61,9 @@ BlockDriverState *bdrv_first;
 
 static BlockDriver *first_drv;
 
+/* If non-zero, use only whitelisted block drivers */
+static int use_bdrv_whitelist;
+
 int path_is_absolute(const char *path)
 {
     const char *p;
@@ -171,6 +174,30 @@ BlockDriver *bdrv_find_format(const char *format_name)
     return NULL;
 }
 
+static int bdrv_is_whitelisted(BlockDriver *drv)
+{
+    static const char *whitelist[] = {
+        CONFIG_BDRV_WHITELIST
+    };
+    const char **p;
+
+    if (!whitelist[0])
+        return 1;               /* no whitelist, anything goes */
+
+    for (p = whitelist; *p; p++) {
+        if (!strcmp(drv->format_name, *p)) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+BlockDriver *bdrv_find_whitelisted_format(const char *format_name)
+{
+    BlockDriver *drv = bdrv_find_format(format_name);
+    return drv && bdrv_is_whitelisted(drv) ? drv : NULL;
+}
+
 int bdrv_create(BlockDriver *drv, const char* filename,
     QEMUOptionParameter *options)
 {
@@ -427,7 +454,10 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
             (flags & (BDRV_O_CACHE_MASK|BDRV_O_NATIVE_AIO));
     else
         open_flags = flags & ~(BDRV_O_FILE | BDRV_O_SNAPSHOT);
-    ret = drv->bdrv_open(bs, filename, open_flags);
+    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv))
+        ret = -ENOTSUP;
+    else
+        ret = drv->bdrv_open(bs, filename, open_flags);
     if ((ret == -EACCES || ret == -EPERM) && !(flags & BDRV_O_FILE)) {
         ret = drv->bdrv_open(bs, filename, open_flags & ~BDRV_O_RDWR);
         bs->read_only = 1;
@@ -1764,6 +1794,12 @@ void bdrv_init(void)
     module_call_init(MODULE_INIT_BLOCK);
 }
 
+void bdrv_init_with_whitelist(void)
+{
+    use_bdrv_whitelist = 1;
+    bdrv_init();
+}
+
 void *qemu_aio_get(AIOPool *pool, BlockDriverState *bs,
                    BlockDriverCompletionFunc *cb, void *opaque)
 {
diff --git a/block.h b/block.h
index 302010d..6b0146f 100644
--- a/block.h
+++ b/block.h
@@ -45,7 +45,9 @@ void bdrv_info(Monitor *mon);
 void bdrv_info_stats(Monitor *mon);
 
 void bdrv_init(void);
+void bdrv_init_with_whitelist(void);
 BlockDriver *bdrv_find_format(const char *format_name);
+BlockDriver *bdrv_find_whitelisted_format(const char *format_name);
 int bdrv_create(BlockDriver *drv, const char* filename,
     QEMUOptionParameter *options);
 int bdrv_create2(BlockDriver *drv,
diff --git a/configure b/configure
index aa2cc43..fb66246 100755
--- a/configure
+++ b/configure
@@ -38,6 +38,7 @@ cc="gcc"
 audio_drv_list=""
 audio_card_list="ac97 es1370 sb16"
 audio_possible_cards="ac97 es1370 sb16 cs4231a adlib gus"
+block_drv_whitelist=""
 host_cc="gcc"
 ar="ar"
 make="make"
@@ -430,6 +431,8 @@ for opt do
   ;;
   --audio-drv-list=*) audio_drv_list="$optarg"
   ;;
+  --block-drv-whitelist=*) block_drv_whitelist=`echo "$optarg" | sed -e 's/,/ /g'`
+  ;;
   --enable-debug-tcg) debug_tcg="yes"
   ;;
   --disable-debug-tcg) debug_tcg="no"
@@ -661,6 +664,8 @@ echo "  --audio-drv-list=LIST    set audio drivers list:"
 echo "                           Available drivers: $audio_possible_drivers"
 echo "  --audio-card-list=LIST   set list of emulated audio cards [$audio_card_list]"
 echo "                           Available cards: $audio_possible_cards"
+echo "  --block-drv-whitelist=L  set block driver whitelist"
+echo "                           (affects only QEMU, not qemu-img)"
 echo "  --enable-mixemu          enable mixer emulation"
 echo "  --disable-xen            disable xen backend driver support"
 echo "  --enable-xen             enable xen backend driver support"
@@ -1826,6 +1831,7 @@ echo "check support     $check_utests"
 echo "mingw32 support   $mingw32"
 echo "Audio drivers     $audio_drv_list"
 echo "Extra audio cards $audio_card_list"
+echo "Block whitelist   $block_drv_whitelist"
 echo "Mixer emulation   $mixemu"
 echo "VNC TLS support   $vnc_tls"
 echo "VNC SASL support  $vnc_sasl"
@@ -1948,6 +1954,7 @@ fi
 if test "$audio_win_int" = "yes" ; then
   echo "CONFIG_AUDIO_WIN_INT=y" >> $config_host_mak
 fi
+echo "CONFIG_BDRV_WHITELIST=$block_drv_whitelist" >> $config_host_mak
 if test "$mixemu" = "yes" ; then
   echo "CONFIG_MIXEMU=y" >> $config_host_mak
 fi
diff --git a/create_config b/create_config
index 30d0487..2f052ae 100755
--- a/create_config
+++ b/create_config
@@ -26,6 +26,13 @@ case $line in
     done
     echo ""
     ;;
+ CONFIG_BDRV_WHITELIST=*)
+    echo "#define CONFIG_BDRV_WHITELIST \\"
+    for drv in ${line#*=}; do
+      echo "    \"${drv}\",\\"
+    done
+    echo "    NULL"
+    ;;
  CONFIG_*=y) # configuration
     name=${line%=*}
     echo "#define $name 1"
diff --git a/hw/xen_disk.c b/hw/xen_disk.c
index 74cde80..5c55251 100644
--- a/hw/xen_disk.c
+++ b/hw/xen_disk.c
@@ -630,7 +630,8 @@ static int blk_init(struct XenDevice *xendev)
 	blkdev->bs = bdrv_new(blkdev->dev);
 	if (blkdev->bs) {
 	    if (bdrv_open2(blkdev->bs, blkdev->filename, qflags,
-                           bdrv_find_format(blkdev->fileproto)) != 0) {
+                           bdrv_find_whitelisted_format(blkdev->fileproto))
+                != 0) {
 		bdrv_delete(blkdev->bs);
 		blkdev->bs = NULL;
 	    }
diff --git a/monitor.c b/monitor.c
index 109ff5c..132fb6e 100644
--- a/monitor.c
+++ b/monitor.c
@@ -596,7 +596,7 @@ static void do_change_block(Monitor *mon, const char *device,
         return;
     }
     if (fmt) {
-        drv = bdrv_find_format(fmt);
+        drv = bdrv_find_whitelisted_format(fmt);
         if (!drv) {
             monitor_printf(mon, "invalid format %s\n", fmt);
             return;
diff --git a/vl.c b/vl.c
index 613cbdb..402e78d 100644
--- a/vl.c
+++ b/vl.c
@@ -2156,7 +2156,7 @@ DriveInfo *drive_init(QemuOpts *opts, void *opaque,
             fprintf(stderr, "\n");
 	    return NULL;
         }
-        drv = bdrv_find_format(buf);
+        drv = bdrv_find_whitelisted_format(buf);
         if (!drv) {
             fprintf(stderr, "qemu: '%s' invalid format\n", buf);
             return NULL;
@@ -5522,7 +5522,7 @@ int main(int argc, char **argv, char **envp)
     /* init the dynamic translator */
     cpu_exec_init_all(tb_size * 1024 * 1024);
 
-    bdrv_init();
+    bdrv_init_with_whitelist();
 
     /* we always create the cdrom drive, even if no disk is there */
     drive_add(NULL, CDROM_ALIAS);