[PATCH] fix read past end of array in md/linear.c

When iterating through an array, one must be careful to test one's index
variable rather than another similarly-named variable.

The loop will read off the end of conf->disks[] in the following
(pathological) case:

  % dd bs=1 seek=840716287 if=/dev/zero of=d1 count=1
  % for i in 2 3 4; do dd if=/dev/zero of=d$i bs=1k count=$(($i+150)); done
  % ./vmlinux ubd0=root ubd1=d1 ubd2=d2 ubd3=d3 ubd4=d4
  # mdadm -C /dev/md0 --level=linear --raid-devices=4 /dev/ubd[1234]

adding some printks, I saw this:

  [42949374.960000] hash_spacing = 821120
  [42949374.960000] cnt          = 4
  [42949374.960000] min_spacing  = 801
  [42949374.960000] j=0 size=820928 sz=820928
  [42949374.960000] i=0 sz=820928 hash_spacing=820928
  [42949374.960000] j=1 size=64 sz=64
  [42949374.960000] j=2 size=64 sz=128
  [42949374.960000] j=3 size=64 sz=192
  [42949374.960000] j=4 size=1515870810 sz=1515871002

Cc: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Neil Brown <neilb@cse.unsw.edu.au>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/linear.c

@@ -188,7 +188,7 @@ static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
 	for (i=0; i < cnt-1 ; i++) {
 		sector_t sz = 0;
 		int j;
-		for (j=i; i<cnt-1 && sz < min_spacing ; j++)
+		for (j = i; j < cnt - 1 && sz < min_spacing; j++)
 			sz += conf->disks[j].size;
 		if (sz >= min_spacing && sz < conf->hash_spacing)
 			conf->hash_spacing = sz;