nvme: Fix discard buffer overrun

This patch checks the discard range array bounds before setting it in
case the driver gets a badly formed request.
Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

drivers/nvme/host/core.c

@@ -518,9 +518,11 @@ static blk_status_t nvme_setup_discard(struct nvme_ns *ns, struct request *req,
 		u64 slba = nvme_block_nr(ns, bio->bi_iter.bi_sector);
 		u32 nlb = bio->bi_iter.bi_size >> ns->lba_shift;
 
+		if (n < segments) {
 			range[n].cattr = cpu_to_le32(0);
 			range[n].nlb = cpu_to_le32(nlb);
 			range[n].slba = cpu_to_le64(slba);
+		}
 		n++;
 	}