zhack: Fix importing large allocation profiles on small pools (#18256)

This patch fixes a segmentation fault in zhack metaslab leak which might
be triggered by feeding zhack with a fragmentation profile that's
exported from a pool larger than the target pool.

Fixes: 8f15d2e4d5
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Paul Dagnelie <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>

Signed-off-by: Mateusz Piotrowski <[email protected]>

cmd/zhack.c

@@ -745,8 +745,11 @@ zhack_do_metaslab_leak(int argc, char **argv)
 			    &start, &size), ==, 2);
 
 			ASSERT(vd);
-			metaslab_t *cur =
-			    vd->vdev_ms[start >> vd->vdev_ms_shift];
+			size_t idx;
+			idx = start >> vd->vdev_ms_shift;
+			if (idx >= vd->vdev_ms_count)
+				continue;
+			metaslab_t *cur = vd->vdev_ms[idx];
 			if (prev != cur) {
 				if (prev) {
 					dmu_tx_commit(tx);