[PATCH 5.10 067/121] perf bpf: Defer freeing string after possible strlen() on it

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

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@xxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/Yg1VtQxKrPpS3uNA@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 tools/perf/util/bpf-loader.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -1215,9 +1215,10 @@ bpf__obj_config_map(struct bpf_object *o
 	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;
 }