Fix for buffer overflow in ldm_frag_add not sufficient

As Ben Hutchings discovered [1], the patch for CVE-2011-1017 (buffer
overflow in ldm_frag_add) is not sufficient.  The original patch in
commit c340b1d6 ("fs/partitions/ldm.c: fix oops caused by corrupted
partition table") does not consider that, for subsequent fragments,
previously allocated memory is used.

[1] http://lkml.org/lkml/2011/5/6/407Reported-by: NBen Hutchings <ben@decadent.org.uk>
Signed-off-by: NTimo Warns <warns@pre-sense.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/partitions/ldm.c

@@ -1335,6 +1335,11 @@ static bool ldm_frag_add (const u8 *data, int size, struct list_head *frags)
 
 	list_add_tail (&f->list, frags);
 found:
+	if (rec >= f->num) {
+		ldm_error("REC value (%d) exceeds NUM value (%d)", rec, f->num);
+		return false;
+	}
+
 	if (f->map & (1 << rec)) {
 		ldm_error ("Duplicate VBLK, part %d.", rec);
 		f->map &= 0x7F;			/* Mark the group as broken */