crush: ensure bucket id is valid before indexing buckets array

BugLink: https://bugs.launchpad.net/bugs/1728739

We were indexing the buckets array without verifying the index was
within the [0,max_buckets) range.  This could happen because
a multistep rule does not have enough buckets and has CRUSH_ITEM_NONE
for an intermediate result, which would feed in CRUSH_ITEM_NONE and
make us crash.

Reflects ceph.git commit 976a24a326da8931e689ee22fce35feab5b67b76.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>
(cherry picked from commit f224a691)
Signed-off-by: Billy Olsen <billy.olsen@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

net/ceph/crush/mapper.c

@@ -888,6 +888,7 @@ int crush_do_rule(const struct crush_map *map,
 			osize = 0;
 
 			for (i = 0; i < wsize; i++) {
+				int bno;
 				/*
 				 * see CRUSH_N, CRUSH_N_MINUS macros.
 				 * basically, numrep <= 0 means relative to
@@ -900,6 +901,13 @@ int crush_do_rule(const struct crush_map *map,
 						continue;
 				}
 				j = 0;
+				/* make sure bucket id is valid */
+				bno = -1 - w[i];
+				if (bno < 0 || bno >= map->max_buckets) {
+					/* w[i] is probably CRUSH_ITEM_NONE */
+					dprintk("  bad w[i] %d\n", w[i]);
+					continue;
+				}
 				if (firstn) {
 					int recurse_tries;
 					if (choose_leaf_tries)
@@ -911,7 +919,7 @@ int crush_do_rule(const struct crush_map *map,
 						recurse_tries = choose_tries;
 					osize += crush_choose_firstn(
 						map,
-						map->buckets[-1-w[i]],
+						map->buckets[bno],
 						weight, weight_max,
 						x, numrep,
 						curstep->arg2,
@@ -930,7 +938,7 @@ int crush_do_rule(const struct crush_map *map,
 						    numrep : (result_max-osize));
 					crush_choose_indep(
 						map,
-						map->buckets[-1-w[i]],
+						map->buckets[bno],
 						weight, weight_max,
 						x, out_size, numrep,
 						curstep->arg2,