mkfs_vfat: fixes for large image cases

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/util-linux/mkfs_vfat.c b/util-linux/mkfs_vfat.c
index 10de2af5b729a23c9d590d49cee6de8a5eb84224..de88a7443dd78674ab24c7f3439597d39ca43d66 100644 (file)
--- a/util-linux/mkfs_vfat.c
+++ b/util-linux/mkfs_vfat.c
@@ -391,16 +391,22 @@ int mkfs_vfat_main(int argc UNUSED_PARAM, char **argv)
        while (1) {
                while (1) {
                        int spf_adj;
-                       off_t tcl = (volume_size_sect - reserved_sect - NUM_FATS * sect_per_fat) / sect_per_clust;
+                       uoff_t tcl = (volume_size_sect - reserved_sect - NUM_FATS * sect_per_fat) / sect_per_clust;
                        // tcl may be > MAX_CLUST_32 here, but it may be
                        // because sect_per_fat is underestimated,
                        // and with increased sect_per_fat it still may become
                        // <= MAX_CLUST_32. Therefore, we do not check
                        // against MAX_CLUST_32, but against a bigger const:
-                       if (tcl > 0x7fffffff)
+                       if (tcl > 0x80ffffff)
                                goto next;
                        total_clust = tcl; // fits in uint32_t
-                       spf_adj = ((total_clust + 2) * 4 + bytes_per_sect - 1) / bytes_per_sect - sect_per_fat;
+                       // Every cluster needs 4 bytes in FAT. +2 entries since
+                       // FAT has space for non-existent clusters 0 and 1.
+                       // Let's see how many sectors that needs.
+                       //May overflow at "*4":
+                       //spf_adj = ((total_clust+2) * 4 + bytes_per_sect-1) / bytes_per_sect - sect_per_fat;
+                       //Same in the more obscure, non-overflowing form:
+                       spf_adj = ((total_clust+2) + (bytes_per_sect/4)-1) / (bytes_per_sect/4) - sect_per_fat;
 #if 0
                        bb_error_msg("sect_per_clust:%u sect_per_fat:%u total_clust:%u",
                                        sect_per_clust, sect_per_fat, (int)tcl);