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From:   Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Date:   Wed, 3 Jul 2019 15:46:06 -0300
To:     Leo Yan <leo.yan@linaro.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Andi Kleen <ak@linux.intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Jin Yao <yao.jin@linux.intel.com>,
        Song Liu <songliubraving@fb.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Alexios Zavras <alexios.zavras@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Changbin Du <changbin.du@intel.com>,
        Eric Saint-Etienne <eric.saint.etienne@oracle.com>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Thomas Richter <tmricht@linux.ibm.com>,
        Alexey Budankov <alexey.budankov@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v1 05/11] perf trace: Smatch: Fix potential NULL pointer
 dereference
Message-ID: <20190703184606.GF10740@kernel.org>
References: <20190702103420.27540-1-leo.yan@linaro.org>
 <20190702103420.27540-6-leo.yan@linaro.org>
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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;
 }