block/dmg: validate chunk size to avoid overflow

Previously the chunk size was not checked, allowing for a large memory
allocation. This patch checks whether the chunks size is within the
resource fork length, and whether the resource fork is below the
trailer of the dmg file.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>

1 files changed, 6 insertions, 1 deletions

diff --git a/block/dmg.c b/block/dmg.c
index 49132499cc..5f6976b25b 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -319,7 +319,7 @@ static int dmg_read_resource_fork(BlockDriverState *bs, DmgHeaderState *ds,
         ret = read_uint32(bs, offset, &count);
         if (ret < 0) {
             goto fail;
-        } else if (count == 0) {
+        } else if (count == 0 || count > info_end - offset) {
             ret = -EINVAL;
             goto fail;
         }
@@ -379,6 +379,11 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
     if (ret < 0) {
         goto fail;
     }
+    if (rsrc_fork_offset >= offset ||
+        rsrc_fork_length > offset - rsrc_fork_offset) {
+        ret = -EINVAL;
+        goto fail;
+    }
     if (rsrc_fork_length != 0) {
         ret = dmg_read_resource_fork(bs, &ds,
                                      rsrc_fork_offset, rsrc_fork_length);