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

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Message-ID: <CAP-5=fXhc-nwVp=HKmycmryYSY6sBrDKGnQ+Ogt+86sHfsT82Q@mail.gmail.com>
Date:   Tue, 28 Mar 2023 22:35:07 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Adrian Hunter <adrian.hunter@...el.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>,
        Namhyung Kim <namhyung@...nel.org>,
        Leo Yan <leo.yan@...aro.org>, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf symbol: Avoid use after free

On Tue, Mar 28, 2023 at 9:52 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> On 29/03/23 02:44, Ian Rogers wrote:
> > 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.
>
> Looks the same as:
>
> https://lore.kernel.org/linux-perf-users/20230316194156.8320-2-adrian.hunter@intel.com/

Sorry for missing that. In the case it returns false, this avoids an
unnecessary snprintf.

Thanks,
Ian

> >
> > 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,
>