shim: Allow data after the end of device path node in load options

When looking for load option optional data, the parser asserts that the
byte after the end of device path node is the same as what the file path
length says it should be. While unusual, it is valid if the end of
device path node comes before the end of the file path list.

That supports some unusual Dell load options where there are two device
paths in the list but the first is terminated by an End Entire Device
Path. Maybe they intended to use an End Device Path Instance node there?
Who knows. Either way, treating it as invalid ends up trying to read
paths from the beginning of the option with obviously poor results.

Fixes: #649

Signed-off-by: Dan Nicholson <dbn@endlessos.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/load-options.c b/load-options.c
index 84fcfb7e..e7b64471 100644
--- a/load-options.c
+++ b/load-options.c
@@ -207,14 +207,14 @@ get_load_option_optional_data(VOID *data, UINT32 data_size,
 		 */
 		i += dp.len;
 	}
-	if (i != fplistlen)
+	if (i > fplistlen)
 		return EFI_INVALID_PARAMETER;
 
 	/*
-	 * if there's any space left, it's "optional data"
+	 * Anything left after the file path list is optional data.
 	 */
-	*od = cur + i;
-	*ods = limit - i;
+	*od = cur + fplistlen;
+	*ods = limit - fplistlen;
 	return EFI_SUCCESS;
 }