block: update string sizes for filename,backing_file,exact_filename

The string field entries 'filename', 'backing_file', and
'exact_filename' in the BlockDriverState struct are defined as 1024
bytes.

However, many places that use these values accept a maximum of PATH_MAX
bytes, so we have a mixture of 1024 byte and PATH_MAX byte allocations.
This patch makes the BlockDriverStruct field string sizes match usage.

This patch also does a few fixes related to the size that needs to
happen now:

    * the block qapi driver is updated to use PATH_MAX bytes
    * the qcow and qcow2 drivers have an additional safety check
    * the block vvfat driver is updated to use PATH_MAX bytes
      for the size of backing_file, for systems where PATH_MAX is < 1024
      bytes.
    * qemu-img uses PATH_MAX rather than 1024.  These instances were not
      changed to be dynamically allocated, however, as the extra
      temporary 3K in stack usage for qemu-img does not seem worrisome.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index e4e690a42b..dbaf016bc7 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -868,7 +868,8 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     /* read the backing file name */
     if (header.backing_file_offset != 0) {
         len = header.backing_file_size;
-        if (len > MIN(1023, s->cluster_size - header.backing_file_offset)) {
+        if (len > MIN(1023, s->cluster_size - header.backing_file_offset) ||
+            len > sizeof(bs->backing_file)) {
             error_setg(errp, "Backing file name too long");
             ret = -EINVAL;
             goto fail;