[PATCH] * grub-core/fs/udf.c: Fix reading label, lvd.ident is dstring

[Pali Rohár]

UDF dstring has stored length in the last byte of buffer. Therefore last
byte is not part of recorded characters. And empty string in dstring is
encoded as empty buffer, including first byte (compression id).
---
I'm not sure how Grub2 should handle empty label. Current patch set
empty buffer for empty label. But it is possible to ignore and do not
set label in this case at all.
---
 grub-core/fs/udf.c |   21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/grub-core/fs/udf.c b/grub-core/fs/udf.c
index 839bff8..e7a4d4e 100644
--- a/grub-core/fs/udf.c
+++ b/grub-core/fs/udf.c
@@ -860,6 +860,25 @@ read_string (const grub_uint8_t *raw, grub_size_t sz, char 
*outbuf)
   return outbuf;
 }
 
+static char *
+read_dstring (const grub_uint8_t *raw, grub_size_t sz, char *outbuf)
+{
+  grub_size_t len;
+
+  if (raw[0] == 0)
+    {
+      if (!outbuf)
+        outbuf = grub_malloc (1);
+      outbuf[0] = 0;
+      return outbuf;
+    }
+
+  len = raw[sz - 1];
+  if (len > sz - 1)
+    len = sz - 1;
+  return read_string (raw, len, outbuf);
+}
+
 static int
 grub_udf_iterate_dir (grub_fshelp_node_t dir,
                      grub_fshelp_iterate_dir_hook_t hook, void *hook_data)
@@ -1197,7 +1216,7 @@ grub_udf_label (grub_device_t device, char **label)
 
   if (data)
     {
-      *label = read_string (data->lvd.ident, sizeof (data->lvd.ident), 0);
+      *label = read_dstring (data->lvd.ident, sizeof (data->lvd.ident), 0);
       grub_free (data);
     }
   else
-- 
1.7.9.5