edac_mc: fix messy kfree calls in the error path

coccinelle warns about:

+ drivers/edac/edac_mc.c:429:9-23: ERROR: reference preceded by free on line 429

421 if (mci->csrows) {
> 422 for (chn = 0; chn < tot_channels; chn++) {
423 csr = mci->csrows[chn];
424 if (csr) {
> 425 for (chn = 0; chn < tot_channels; chn++)
426 kfree(csr->channels[chn]);
427 kfree(csr);
428 }
> 429 kfree(mci->csrows[i]);
430 }
431 kfree(mci->csrows);
432 }

and that code block seem to mess things up in several ways (double free, memory
leak, out-of-bound reads etc.):

L422: The iterator "chn" and bound "tot_channels" are totally wrong. Should be
"row" and "tot_csrows" respectively. Which means either memory leak, or
out-of-bound reads (which if does not trigger an immediate page fault
error, will further lead to kfree() on random addresses).

L425: The inner loop is reusing the same iterator "chn" as the outer loop,
which could lead to premature end of the outer loop, and hence memory leak.

L429: The array index 'i' in mci->csrows[i] is a temporary value used in
previous loops, and won't change at all in the current loop. Which
means either out-of-bound read and possibly kfree(random number), or the
same mci->csrows[i] get freed once and again, and possibly double free
for the kfree(csr) in L427.

L426/L427: a kfree(csr->channels) is needed in between to avoid leaking the memory.

The buggy code was introduced by commit de3910eb ("edac: change the mem
allocation scheme to make Documentation/kobject.txt happy") in the 3.6-rc1
merge window. Fix it by freeing up resources in this order:

free csrows[i]->channels[j]
free csrows[i]->channels
free csrows[i]
free csrows

CC: Mauro Carvalho Chehab <[e-mail]>
CC: Shaun Ruffell <[e-mail]>
Signed-off-by: Fengguang Wu <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/edac/edac_mc.c

···
 		kfree(mci->dimms);
 	}
 	if (mci->csrows) {
-		for (chn = 0; chn < tot_channels; chn++) {
-			csr = mci->csrows[chn];
+		for (row = 0; row < tot_csrows; row++) {
+			csr = mci->csrows[row];
 			if (csr) {
-				for (chn = 0; chn < tot_channels; chn++)
-					kfree(csr->channels[chn]);
+				if (csr->channels) {
+					for (chn = 0; chn < tot_channels; chn++)
+						kfree(csr->channels[chn]);
+					kfree(csr->channels);
+				}
 				kfree(csr);
 			}
-			kfree(mci->csrows[i]);
 		}
 		kfree(mci->csrows);
 	}