linux-kernel - [PATCH v1] perf symbol: Avoid use after free

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Message-Id: <20230328234413.1081014-1-irogers@google.com>
Date:   Tue, 28 Mar 2023 16:44:13 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Leo Yan <leo.yan@...aro.org>, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1] perf symbol: Avoid use after free

If demangling succeeds then sym_name is set to the demangled string
that is freed. Rather than test if sym_name is empty and possibly
use-after-free on the return path, expand out the alternatives.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/symbol-elf.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index c0a2de42c51b..b7e3e492bff3 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -577,15 +577,17 @@ static bool get_plt_got_name(GElf_Shdr *shdr, size_t i,
 	/* Get the associated symbol */
 	gelf_getsym(di->dynsym_data, vr->sym_idx, &sym);
 	sym_name = elf_sym__name(&sym, di->dynstr_data);
-	demangled = demangle_sym(di->dso, 0, sym_name);
-	if (demangled != NULL)
-		sym_name = demangled;
-
-	snprintf(buf, buf_sz, "%s@plt", sym_name);
-
-	free(demangled);
+	if (*sym_name == '\0')
+		return false;
 
-	return *sym_name;
+	demangled = demangle_sym(di->dso, 0, sym_name);
+	if (demangled != NULL) {
+		snprintf(buf, buf_sz, "%s@plt", demangled);
+		free(demangled);
+	} else {
+		snprintf(buf, buf_sz, "%s@plt", sym_name);
+	}
+	return true;
 }
 
 static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,
-- 
2.40.0.348.gf938b09366-goog