Re: [PATCH] fix an infinite loop with a corrupted pc partition table

[Felix Zielcke <fzielcke@z-51.de>]

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Am Freitag, den 24.07.2009, 18:58 +0200 schrieb Felix Zielcke:
> 
> 
> With this [0] partition table grub-probe currently loops forever:
> 
> kern/disk.c:389: Reading `hd1'...
> partmap/pc.c:142: partition 0: flag 0x0, type 0x5, start 0x0, len
> 0x11177330
> partmap/pc.c:142: partition 1: flag 0x0, type 0x0, start 0x0, len 0x0
> partmap/pc.c:142: partition 2: flag 0x0, type 0x0, start 0x0, len 0x0
> partmap/pc.c:142: partition 3: flag 0x0, type 0x0, start 0x0, len 0x0
> kern/disk.c:389: Reading `hd1'...
> partmap/pc.c:142: partition 0: flag 0x0, type 0x5, start 0x0, len
> 0x11177330
> partmap/pc.c:142: partition 1: flag 0x0, type 0x0, start 0x0, len 0x0
> partmap/pc.c:142: partition 2: flag 0x0, type 0x0, start 0x0, len 0x0
> partmap/pc.c:142: partition 3: flag 0x0, type 0x0, start 0x0, len 0x0
> [...]
> 
> This patch fixes it, but probable there's a better fix.
> 
> 
> [0]
> http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=corrupt-table.dat;att=1;bug=519223 

Here's a new one after comments from Vladimir on IRC
loop count is increased to 100'000 and partitions with a starting sector
of 0 are ignored.

-- 
Felix Zielcke

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2009-07-24  Felix Zielcke  <fzielcke@z-51.de>

	* partmap/pc.c (pc_partition_map_iterate): Don't loop forever
	in case the partition table is corrupted.  Also ignore partitions
	with a starting sector of 0.

diff --git a/partmap/pc.c b/partmap/pc.c
index 6f68ecf..ab58b3d 100644
--- a/partmap/pc.c
+++ b/partmap/pc.c
@@ -97,6 +97,7 @@ pc_partition_map_iterate (grub_disk_t disk,
   struct grub_pc_partition_mbr mbr;
   struct grub_pc_partition_disk_label label;
   struct grub_disk raw;
+  int loop;
 
   /* Enforce raw disk access.  */
   raw = *disk;
@@ -108,11 +109,13 @@ pc_partition_map_iterate (grub_disk_t disk,
   p.data = &pcdata;
   p.partmap = &grub_pc_partition_map;
 
-  while (1)
+  loop = 0;
+  while (loop < 100000)
     {
       int i;
       struct grub_pc_partition_entry *e;
 
+      loop++;
       /* Read the MBR.  */
       if (grub_disk_read (&raw, p.offset, 0, sizeof (mbr), &mbr))
 	goto finish;
@@ -143,7 +146,7 @@ pc_partition_map_iterate (grub_disk_t disk,
 	    return grub_error (GRUB_ERR_BAD_PART_TABLE, "dummy mbr");
 
 	  /* If this partition is a normal one, call the hook.  */
-	  if (! grub_pc_partition_is_empty (e->type)
+	  if (e->start != 0 && ! grub_pc_partition_is_empty (e->type)
 	      && ! grub_pc_partition_is_extended (e->type))
 	    {
 	      pcdata.dos_part++;
@@ -206,7 +209,7 @@ pc_partition_map_iterate (grub_disk_t disk,
 	{
 	  e = mbr.entries + i;
 
-	  if (grub_pc_partition_is_extended (e->type))
+	  if (e->start != 0 && grub_pc_partition_is_extended (e->type))
 	    {
 	      p.offset = pcdata.ext_offset + grub_le_to_cpu32 (e->start);
 	      if (! pcdata.ext_offset)
@@ -221,6 +224,8 @@ pc_partition_map_iterate (grub_disk_t disk,
 	break;
     }
 
+  if (loop == 100000)
+    return grub_error (GRUB_ERR_BAD_PART_TABLE, "Corrupted partition table found.");
  finish:
   return grub_errno;
 }