[int13] Avoid potential division by zero

Avoid using a zero sector count to guess the disk geometry, since that
would result in a division by zero when calculating the number of
cylinders.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/arch/x86/interface/pcbios/int13.c b/src/arch/x86/interface/pcbios/int13.c
index 6f16904df91d60067125fb917cb23e3348b0c4d2..8b2e134b5d47d540c64818161f41b5b47b5c75cc 100644 (file)
--- a/src/arch/x86/interface/pcbios/int13.c
+++ b/src/arch/x86/interface/pcbios/int13.c
@@ -561,6 +561,8 @@ static int int13_guess_geometry_hdd ( struct int13_drive *int13, void *scratch,
        struct master_boot_record *mbr = scratch;
        struct partition_table_entry *partition;
        unsigned int i;
+       unsigned int end_head;
+       unsigned int end_sector;
        int rc;
 
        /* Default guess is xx/255/63 */
@@ -586,10 +588,12 @@ static int int13_guess_geometry_hdd ( struct int13_drive *int13, void *scratch,
         */
        for ( i = 0 ; i < 4 ; i++ ) {
                partition = &mbr->partitions[i];
-               if ( ! partition->type )
+               end_head = PART_HEAD ( partition->chs_end );
+               end_sector = PART_SECTOR ( partition->chs_end );
+               if ( ! ( partition->type && end_head && end_sector ) )
                        continue;
-               *heads = ( PART_HEAD ( partition->chs_end ) + 1 );
-               *sectors = PART_SECTOR ( partition->chs_end );
+               *heads = ( end_head + 1 );
+               *sectors = end_sector;
                DBGC ( int13, "INT13 drive %02x guessing C/H/S xx/%d/%d based "
                       "on partition %d\n",
                       int13->drive, *heads, *sectors, ( i + 1 ) );