From c51a227fd9a85e85e925d31a8f525e67d865ee0a Mon Sep 17 00:00:00 2001
From: Henry Gabryjelski <henrygab@users.noreply.github.com>
Date: Wed, 13 Mar 2019 15:20:42 -0700
Subject: [PATCH] Add static assert This guards against future increase in
 number of files causing buffer overflow when reading the first root directory
 sector.

---
 src/usb/uf2/ghostfat.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/usb/uf2/ghostfat.c b/src/usb/uf2/ghostfat.c
index 1f41c10..7262bfc 100644
--- a/src/usb/uf2/ghostfat.c
+++ b/src/usb/uf2/ghostfat.c
@@ -97,6 +97,11 @@ static struct TextFile const info[] = {
 #define START_ROOTDIR      (START_FAT1 + SECTORS_PER_FAT)
 #define START_CLUSTERS     (START_ROOTDIR + ROOT_DIR_SECTORS)
 
+// all directory entries must fit in a single sector
+// because otherwise current code overflows buffer
+STATIC_ASSERT(NUM_INFO < (512 / sizeof(DirEntry)));
+
+
 static FAT_BootBlock const BootBlock = {
     .JumpInstruction      = {0xeb, 0x3c, 0x90},
     .OEMInfo              = "UF2 UF2 ",
@@ -198,6 +203,7 @@ void read_block(uint32_t block_no, uint8_t *data) {
                 ((uint16_t *)(void *)data)[i] = v == UF2_LAST_SECTOR ? 0xffff : v + 1;
         }
     } else if (block_no < START_CLUSTERS) {
+        // Use STATIC_ASSERT() above to ensure only first sector has entries
         sectionIdx -= START_ROOTDIR;
         if (sectionIdx == 0) {
             DirEntry *d = (void *)data;