perf bpf: Defer freeing string after possible strlen() on it

commit 31ded1535e3182778a1d0e5c32711f55da3bc512 upstream.

This was detected by the gcc in Fedora Rawhide's gcc:

  50    11.01 fedora:rawhide                : FAIL gcc version 12.0.1 20220205 (Red Hat 12.0.1-0) (GCC)
        inlined from 'bpf__config_obj' at util/bpf-loader.c:1242:9:
    util/bpf-loader.c:1225:34: error: pointer 'map_opt' may be used after 'free' [-Werror=use-after-free]
     1225 |                 *key_scan_pos += strlen(map_opt);
          |                                  ^~~~~~~~~~~~~~~
    util/bpf-loader.c:1223:9: note: call to 'free' here
     1223 |         free(map_name);
          |         ^~~~~~~~~~~~~~
    cc1: all warnings being treated as errors

So do the calculations on the pointer before freeing it.

Fixes: 04f9bf2bac72480c ("perf bpf-loader: Add missing '*' for key_scan_pos")
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang ShaoBo <bobo.shaobowang@huawei.com>
Link: https://lore.kernel.org/lkml/Yg1VtQxKrPpS3uNA@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index fbb3c40..71710a1 100644 (file)
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -1214,9 +1214,10 @@ bpf__obj_config_map(struct bpf_object *obj,
        pr_debug("ERROR: Invalid map config option '%s'\n", map_opt);
        err = -BPF_LOADER_ERRNO__OBJCONF_MAP_OPT;
 out:
-       free(map_name);
        if (!err)
                *key_scan_pos += strlen(map_opt);
+
+       free(map_name);
        return err;
 }