linux-kernel - [PATCH 1/1] perf bpf: Defer freeing string after possible strlen() on it

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Date:   Wed, 16 Feb 2022 16:51:17 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Wang ShaoBo <bobo.shaobowang@...wei.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Ian Rogers <irogers@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/1] perf bpf: Defer freeing string after possible strlen()
 on it

FYI: I'm carrying this on my tree:

---

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@...el.com>
Cc: Ian Rogers <irogers@...gle.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Wang ShaoBo <bobo.shaobowang@...wei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/bpf-loader.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index 7ecfaac7536a1b1b..16ec605a9fe46a64 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -1220,9 +1220,10 @@ 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;
 }
 
-- 
2.34.1