qcow1: Check maximum cluster size

Huge values for header.cluster_bits cause unbounded allocations (e.g.
for s->cluster_cache) and crash qemu this way. Less huge values may
survive those allocations, but can cause integer overflows later on.

The only cluster sizes that qemu can create are 4k (for standalone
images) and 512 (for images with backing files), so we can limit it
to 64k.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>

1 files changed, 8 insertions, 2 deletions

diff --git a/block/qcow.c b/block/qcow.c
index 3684794dee..e60df234c4 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -128,11 +128,17 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    if (header.size <= 1 || header.cluster_bits < 9) {
-        error_setg(errp, "invalid value in qcow header");
+    if (header.size <= 1) {
+        error_setg(errp, "Image size is too small (must be at least 2 bytes)");
         ret = -EINVAL;
         goto fail;
     }
+    if (header.cluster_bits < 9 || header.cluster_bits > 16) {
+        error_setg(errp, "Cluster size must be between 512 and 64k");
+        ret = -EINVAL;
+        goto fail;
+    }
+
     if (header.crypt_method > QCOW_CRYPT_AES) {
         error_setg(errp, "invalid encryption method in qcow header");
         ret = -EINVAL;