linux-kernel - Re: [PATCH v1 05/11] perf trace: Smatch: Fix potential NULL pointer dereference

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Date:   Wed, 3 Jul 2019 15:46:06 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Andi Kleen <ak@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Davidlohr Bueso <dave@...olabs.net>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Changbin Du <changbin.du@...el.com>,
        Eric Saint-Etienne <eric.saint.etienne@...cle.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1 05/11] perf trace: Smatch: Fix potential NULL pointer
 dereference

Em Tue, Jul 02, 2019 at 06:34:14PM +0800, Leo Yan escreveu:
> Based on the following report from Smatch, fix the potential
> NULL pointer dereference check.
> 
>   tools/perf/builtin-trace.c:1044
>   thread_trace__new() error: we previously assumed 'ttrace' could be
>   null (see line 1041).
> 
> tools/perf/builtin-trace.c
> 1037 static struct thread_trace *thread_trace__new(void)
> 1038 {
> 1039         struct thread_trace *ttrace =  zalloc(sizeof(struct thread_trace));
> 1040
> 1041         if (ttrace)
> 1042                 ttrace->files.max = -1;
> 1043
> 1044         ttrace->syscall_stats = intlist__new(NULL);
>              ^^^^^^^^
> 1045
> 1046         return ttrace;
> 1047 }
> 
> This patch directly returns NULL when fail to allocate memory for
> ttrace; this can avoid potential NULL pointer dereference.

I did it slightly different, to avoid having two return lines, and that
is what most other constructors (foo__new()) do in tools/perf/, kept
your changeset comment and patch authorship, thanks.

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index d0eb7224dd36..e3fc9062f136 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1038,10 +1038,10 @@ static struct thread_trace *thread_trace__new(void)
 {
 	struct thread_trace *ttrace =  zalloc(sizeof(struct thread_trace));
 
-	if (ttrace)
+	if (ttrace) {
 		ttrace->files.max = -1;
-
-	ttrace->syscall_stats = intlist__new(NULL);
+		ttrace->syscall_stats = intlist__new(NULL);
+	}
 
 	return ttrace;
 }