linux-kernel - Re: [PATCH v1 1/3] perf disasm: Fix capstone memory leak

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Message-ID: <ZvOmXH7gKzGKSh7y@google.com>
Date: Tue, 24 Sep 2024 22:57:48 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: 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>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Kajol Jain <kjain@...ux.ibm.com>,
	Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
	"Steinar H. Gunderson" <sesse@...gle.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Yang Jihong <yangjihong@...edance.com>, leo.yan@....com
Subject: Re: [PATCH v1 1/3] perf disasm: Fix capstone memory leak

On Tue, Sep 24, 2024 at 12:51:20PM -0700, Ian Rogers wrote:
> On Tue, Sep 24, 2024 at 11:38 AM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > On Mon, Sep 23, 2024 at 05:37:18PM -0700, Ian Rogers wrote:
> > > The insn argument passed to cs_disasm needs freeing. To support
> > > accurately having count, add an additional free_count variable.
> > >
> > > Fixes: c5d60de1813a ("perf annotate: Add support to use libcapstone in powerpc")
> > > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > > ---
> > >  tools/perf/util/disasm.c | 11 +++++++----
> > >  1 file changed, 7 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
> > > index f05ba7739c1e..2c8063660f2e 100644
> > > --- a/tools/perf/util/disasm.c
> > > +++ b/tools/perf/util/disasm.c
> > > @@ -1627,12 +1627,12 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
> > >       u64 start = map__rip_2objdump(map, sym->start);
> > >       u64 len;
> > >       u64 offset;
> > > -     int i, count;
> > > +     int i, count, free_count;
> > >       bool is_64bit = false;
> > >       bool needs_cs_close = false;
> > >       u8 *buf = NULL;
> > >       csh handle;
> > > -     cs_insn *insn;
> > > +     cs_insn *insn = NULL;
> > >       char disasm_buf[512];
> > >       struct disasm_line *dl;
> > >
> > > @@ -1664,7 +1664,7 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
> > >
> > >       needs_cs_close = true;
> > >
> > > -     count = cs_disasm(handle, buf, len, start, len, &insn);
> > > +     free_count = count = cs_disasm(handle, buf, len, start, len, &insn);
> > >       for (i = 0, offset = 0; i < count; i++) {
> > >               int printed;
> > >
> > > @@ -1702,8 +1702,11 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
> > >       }
> > >
> > >  out:
> > > -     if (needs_cs_close)
> > > +     if (needs_cs_close) {
> > >               cs_close(&handle);
> > > +             if (free_count > 0)
> > > +                     cs_free(insn, free_count);
> >
> > It seems cs_free() can handle NULL insn and 0 free_count (like regular free)
> > so we can call it unconditionally.
> 
> No, on error from cs_disasm free_count gets assigned -1 and my
> experience was things crashing.
 
Ok then, I thought it returns 0 on error.

Thanks,
Namhyung

> >
> > > +     }
> > >       free(buf);
> > >       return count < 0 ? count : 0;
> > >
> > > --
> > > 2.46.0.792.g87dc391469-goog
> > >