Re: [PATCH v1 04/11] perf annotate: Smatch: Fix dereferencing freed memory

From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Leo Yan <leo.yan@linaro.org>
Cc: Song Liu <songliubraving@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	linux-kernel@vger.kernel.org, Jin Yao <yao.jin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Andi Kleen <ak@linux.intel.com>,
	Eric Saint-Etienne <eric.saint.etienne@oracle.com>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	Ingo Molnar <mingo@redhat.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Alexios Zavras <alexios.zavras@intel.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Namhyung Kim <namhyung@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Thomas Richter <tmricht@linux.ibm.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	Changbin Du <changbin.du@intel.com>,
	Alexey Budankov <alexey.budankov@linux.intel.com>
Subject: Re: [PATCH v1 04/11] perf annotate: Smatch: Fix dereferencing freed memory
Date: Wed, 3 Jul 2019 15:43:46 -0300	[thread overview]
Message-ID: <20190703184346.GE10740@kernel.org> (raw)
In-Reply-To: <20190702103420.27540-5-leo.yan@linaro.org>

Em Tue, Jul 02, 2019 at 06:34:13PM +0800, Leo Yan escreveu:
> Based on the following report from Smatch, fix the potential
> dereferencing freed memory check.
> 
>   tools/perf/util/annotate.c:1125
>   disasm_line__parse() error: dereferencing freed memory 'namep'
> 
> tools/perf/util/annotate.c
> 1100 static int disasm_line__parse(char *line, const char **namep, char **rawp)
> 1101 {
> 1102         char tmp, *name = ltrim(line);
> 
> [...]
> 
> 1114         *namep = strdup(name);
> 1115
> 1116         if (*namep == NULL)
> 1117                 goto out_free_name;
> 
> [...]
> 
> 1124 out_free_name:
> 1125         free((void *)namep);
>                           ^^^^^
> 1126         *namep = NULL;
>              ^^^^^^
> 1127         return -1;
> 1128 }
> 
> If strdup() fails to allocate memory space for *namep, we don't need to
> free memory with pointer 'namep', which is resident in data structure
> disasm_line::ins::name; and *namep is NULL pointer for this failure, so
> it's pointless to assign NULL to *namep again.

Applied, with this extra comment:

Committer note:

Freeing namep, which is the address of the first entry of the 'struct
ins' that is the first member of struct disasm_line would in fact free
that disasm_line instance, if it was allocated via malloc/calloc, which,
later, would a dereference of freed memory.

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