vmdk: Don't corrupt desc file in vmdk_write_cid

If the text description file is larger than DESC_SIZE, we force the last
byte in the buffer to be 0 and write it out.

This results in a corruption.

Try to allocate a big buffer in this case.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1923

Signed-off-by: Fam Zheng <fam@euphon.net>
Message-ID: <20231124115654.3239137-1-fam@euphon.net>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 20 insertions, 8 deletions

diff --git a/block/vmdk.c b/block/vmdk.c
index d87f6d9..d6971c7 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -351,29 +351,41 @@ vmdk_write_cid(BlockDriverState *bs, uint32_t cid)
     BDRVVmdkState *s = bs->opaque;
     int ret = 0;
 
-    desc = g_malloc0(DESC_SIZE);
-    tmp_desc = g_malloc0(DESC_SIZE);
-    ret = bdrv_co_pread(bs->file, s->desc_offset, DESC_SIZE, desc, 0);
+    size_t desc_buf_size;
+
+    if (s->desc_offset == 0) {
+        desc_buf_size = bdrv_getlength(bs->file->bs);
+        if (desc_buf_size > 16ULL << 20) {
+            error_report("VMDK description file too big");
+            return -EFBIG;
+        }
+    } else {
+        desc_buf_size = DESC_SIZE;
+    }
+
+    desc = g_malloc0(desc_buf_size);
+    tmp_desc = g_malloc0(desc_buf_size);
+    ret = bdrv_co_pread(bs->file, s->desc_offset, desc_buf_size, desc, 0);
     if (ret < 0) {
         goto out;
     }
 
-    desc[DESC_SIZE - 1] = '\0';
+    desc[desc_buf_size - 1] = '\0';
     tmp_str = strstr(desc, "parentCID");
     if (tmp_str == NULL) {
         ret = -EINVAL;
         goto out;
     }
 
-    pstrcpy(tmp_desc, DESC_SIZE, tmp_str);
+    pstrcpy(tmp_desc, desc_buf_size, tmp_str);
     p_name = strstr(desc, "CID");
     if (p_name != NULL) {
         p_name += sizeof("CID");
-        snprintf(p_name, DESC_SIZE - (p_name - desc), "%" PRIx32 "\n", cid);
-        pstrcat(desc, DESC_SIZE, tmp_desc);
+        snprintf(p_name, desc_buf_size - (p_name - desc), "%" PRIx32 "\n", cid);
+        pstrcat(desc, desc_buf_size, tmp_desc);
     }
 
-    ret = bdrv_co_pwrite_sync(bs->file, s->desc_offset, DESC_SIZE, desc, 0);
+    ret = bdrv_co_pwrite_sync(bs->file, s->desc_offset, desc_buf_size, desc, 0);
 
 out:
     g_free(desc);