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, 2 deletions

diff --git a/qemu-img.c b/qemu-img.c
index 7876258..4e9a7f5 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -2556,7 +2556,7 @@ static int img_rebase(int argc, char **argv)
 
     /* For safe rebasing we need to compare old and new backing file */
     if (!unsafe) {
-        char backing_name[1024];
+        char backing_name[PATH_MAX];
 
         blk_old_backing = blk_new_with_bs("old_backing", &error_abort);
         bs_old_backing = blk_bs(blk_old_backing);
@@ -2614,7 +2614,7 @@ static int img_rebase(int argc, char **argv)
         }
         old_backing_num_sectors = bdrv_nb_sectors(bs_old_backing);
         if (old_backing_num_sectors < 0) {
-            char backing_name[1024];
+            char backing_name[PATH_MAX];
 
             bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
             error_report("Could not get size of '%s': %s",