lib/ftl: check for null

Fixes #726.
This prevents a segmentation fault by checking the pointer
before accessing it.

Change-Id: I18a3776fbcd6242c6efd1b88044debaa88c7342f
Signed-off-by: Claire J. In <claire.in@circuitblvd.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/449591
Reviewed-by: wuzhouhui <wuzhouhui@kingsoft.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>

lib/ftl/ftl_io.c

@@ -256,6 +256,10 @@ ftl_io_erase_init(struct ftl_band *band, size_t lbk_cnt, spdk_ftl_fn cb)
 	};
 
 	io = ftl_io_init_internal(&opts);
+	if (!io) {
+		return NULL;
+	}
+
 	io->lbk_cnt = lbk_cnt;
 
 	return io;

lib/ftl/ftl_reloc.c

@@ -454,7 +454,13 @@ ftl_reloc_io_init(struct ftl_band_reloc *breloc, struct ftl_io *io,
 	}
 
 	io = ftl_io_init_internal(&opts);
+	if (!io) {
+		spdk_dma_free(opts.data);
+		return -1;
+	}
+
 	io->ppa = ppa;
+
 	return 0;
 }