Fix bpb_is_sane() cluster size calculation for non-512 byte sectors.

bpb_is_sane() used to effectively multiplying the sector size (relative
to 512 bytes) twice, which meant that filesystems with e.g. 2K sectors and
32 sectors per cluster were rejected because while this adds up to 64K
clusters (i.e. the upper limit), the calculation wrongly came to 256K.

This bug tends to affect 5.5G ipods when formatted using dosfstools.

Change-Id: Ia3f1e1303b2af953f497ccdbf23cd49c3d72e46a

1 files changed, 9 insertions, 4 deletions

diff --git a/firmware/drivers/fat.c b/firmware/drivers/fat.c
index 0b8451a5c6..fb75355898 100644
--- a/firmware/drivers/fat.c
+++ b/firmware/drivers/fat.c
@@ -624,13 +624,18 @@ static int bpb_is_sane(IF_MV_NONVOID(struct bpb* fat_bpb))
                 fat_bpb->bpb_bytspersec);
         return -1;
     }
-    if((long)fat_bpb->bpb_secperclus * (long)fat_bpb->bpb_bytspersec
-                                                                   > 128L*1024L)
+    if((long)fat_bpb->bpb_secperclus * SECTOR_SIZE > 128L*1024L)
     {
+        /* We don't multiply by bpb_bytspersec here, because
+         * back in fat_mount_internal() bpb_secperclus has been
+         * "normalised" to 512 byte clusters, by multiplying with
+         * secmult. */
         DEBUGF( "bpb_is_sane() - Error: cluster size is larger than 128K "
                 "(%d * %d = %d)\n",
-                fat_bpb->bpb_bytspersec, fat_bpb->bpb_secperclus,
-                fat_bpb->bpb_bytspersec * fat_bpb->bpb_secperclus);
+                fat_bpb->bpb_bytspersec,
+                fat_bpb->bpb_secperclus / (fat_bpb->bpb_bytspersec / SECTOR_SIZE),
+                fat_bpb->bpb_bytspersec * fat_bpb->bpb_secperclus /
+                (fat_bpb->bpb_bytspersec / SECTOR_SIZE));
         return -2;
     }
     if(fat_bpb->bpb_numfats != 2)