qcow2: Reject too large header extensions

Image files that make qemu-img info read several gigabytes into the
unknown header extensions list are bad. Just fail opening the image
if an extension claims to be larger than the header extension area.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index f68f0e107..eb5ea485d 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -108,6 +108,11 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
 #ifdef DEBUG_EXT
         printf("ext.magic = 0x%x\n", ext.magic);
 #endif
+        if (ext.len > end_offset - offset) {
+            error_report("Header extension too large");
+            return -EINVAL;
+        }
+
         switch (ext.magic) {
         case QCOW2_EXT_MAGIC_END:
             return 0;