[coverity] fat.c fatlong_parse_entry() buffer overrun, fix warning basisname

BYTES2INT16() uses [i + 0] and [i + 1] therefore 30 is the max element
available in the raw byte array of size 32

 (((uint32_t)array[pos+0] << 0) | \
 ((uint32_t)array[pos+1] << 8))

 struct /* raw byte array */
 {
     uint8_t  data[32];
 };

 basisname is only uninitialized in the . and .. dir entries
both are likely false positives but cheap enough to guard against

Change-Id: Iab3d186fed6050d2d61185071765a2c0feb9515f

1 files changed, 6 insertions, 2 deletions

diff --git a/firmware/drivers/fat.c b/firmware/drivers/fat.c
index 20c8f2b8e0..ebf0f92798 100644
--- a/firmware/drivers/fat.c
+++ b/firmware/drivers/fat.c
@@ -659,11 +659,14 @@ static inline unsigned int longent_char_next(unsigned int i)
 {
     switch (i += 2)
     {
+    /* flip endian for elements 14 - 27 */
     case 26: i -= 1; /* return 28 */
+    /* Fall-Through */
     case 11: i += 3; /* return 14 */
     }
-
-    return i < 32 ? i : 0;
+    /* BYTES2INT16() uses [i + 0] and [i + 1] therefore
+     * 30 is the max element available in the raw byte array of size 32 */
+    return i < 31 ? i : 0;
 }
 
 /* initialize the parse state; call before parsing first long entry */
@@ -1708,6 +1711,7 @@ static int add_dir_entry(struct bpb *fat_bpb, struct fat_filestr *parentstr,
         int dots = strlcpy(shortname, name, 11);
         memset(&shortname[dots], ' ', 11 - dots);
         entries_needed = 1;
+        basisname[0] = '\0';
     }
     else
     {