Merge pull request #751 from DKWDRV/bdm_fatFS_fix2

bdm MBR add extra checks for invalid MBR (VBR)

Author: rickgaiser

iop/fs/bdm/src/part_driver_mbr.c

@@ -9,13 +9,37 @@
 
 #include "module_debug.h"
 
+int partitions_sanity_check_mbr(struct block_device *bd, master_boot_record* pMbrBlock) {
+    //All 4 MBR partitions should be considered valid ones to be mounted, even if some are unused.
+    //At least one of them must be active.
+    int valid = 0;
+    int active = 0;
+    
+    for (int i = 0; i < 4; i++)
+    {
+        
+        if (pMbrBlock->primary_partitions[i].partition_type != 0) {
+            
+            if((pMbrBlock->primary_partitions[i].first_lba == 0) || (pMbrBlock->primary_partitions[i].first_lba >= bd->sectorCount))
+                return 0; //invalid
+            
+            active++;
+        }
+        
+        valid++; //Considered at least a valid partition.
+    }
+    
+    return (valid == 4) && (active > 0);
+}
+
 int part_connect_mbr(struct block_device *bd)
 {
     master_boot_record* pMbrBlock = NULL;
     int rval = -1;
     int ret;
     int mountCount = 0;
     int partIndex;
+    int valid_partitions;
 
     M_DEBUG("%s\n", __func__);
 
@@ -59,14 +83,29 @@ int part_connect_mbr(struct block_device *bd)
         return rval;
     }
 
-    // Loop and parse the primary partition entries in the MBR block.
+    
+    valid_partitions = partitions_sanity_check_mbr(bd, pMbrBlock);
+
+    //Most likely a VBR
+    if(valid_partitions == 0) {
+        printf("MBR disk valid_partitions=%d \n", valid_partitions);
+        FreeSysMemory(pMbrBlock);
+        return -1;
+    }
+
     printf("Found MBR disk\n");
+
+    // Loop and parse the primary partition entries in the MBR block.
     for (int i = 0; i < 4; i++)
     {
         // Check if the partition is active, checking the status bit is not reliable so check if the sector_count is greater than zero instead.
         if (pMbrBlock->primary_partitions[i].sector_count == 0)
             continue;
 
+        //Ignore partitions that are not active. 0 is empty partition_type.
+        if (pMbrBlock->primary_partitions[i].partition_type == 0)
+            continue;
+
         printf("Found partition type 0x%02x\n", pMbrBlock->primary_partitions[i].partition_type);
 
         // TODO: Filter out unsupported partition types.
@@ -96,4 +135,4 @@ int part_connect_mbr(struct block_device *bd)
 
     FreeSysMemory(pMbrBlock);
     return rval;
-}
+}