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From:   Ian Rogers <irogers@google.com>
Date:   Wed, 8 Jul 2020 17:54:47 -0700
Message-ID: <CAP-5=fVx1YqNOja4GCAVApQ05BW5Z6CWbAENU3kVCzxJOyKySA@mail.gmail.com>
Subject: Re: [PATCH v2] Fix annotate.c use of uninitialized value error
To:     Jiri Olsa <jolsa@redhat.com>
Cc:     Numfor Mbiziwo-Tiapo <nums@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Song Liu <songliubraving@fb.com>, mbd@fb.com,
        LKML <linux-kernel@vger.kernel.org>,
        Stephane Eranian <eranian@google.com>
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On Fri, Oct 25, 2019 at 3:11 PM Ian Rogers <irogers@google.com> wrote:
>
> It looks like this wasn't merged to tip. Does anything need addressing
> to get it merged?
>
> Thanks,
> Ian
>
> On Wed, Aug 7, 2019 at 4:32 AM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > On Mon, Jul 29, 2019 at 01:57:50PM -0700, Numfor Mbiziwo-Tiapo wrote:
> > > Our local MSAN (Memory Sanitizer) build of perf throws a warning
> > > that comes from the "dso__disassemble_filename" function in
> > > "tools/perf/util/annotate.c" when running perf record.
> > >
> > > The warning stems from the call to readlink, in which "build_id_path"
> > > was being read into "linkname". Since readlink does not null terminate,
> > > an uninitialized memory access would later occur when "linkname" is
> > > passed into the strstr function. This is simply fixed by null-terminating
> > > "linkname" after the call to readlink.
> > >
> > > To reproduce this warning, build perf by running:
> > > make -C tools/perf CLANG=1 CC=clang EXTRA_CFLAGS="-fsanitize=memory\
> > >  -fsanitize-memory-track-origins"
> > >
> > > (Additionally, llvm might have to be installed and clang might have to
> > > be specified as the compiler - export CC=/usr/bin/clang)
> > >
> > > then running:
> > > tools/perf/perf record -o - ls / | tools/perf/perf --no-pager annotate\
> > >  -i - --stdio
> > >
> > > Please see the cover letter for why false positive warnings may be
> > > generated.
> > >
> > > Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
> >
> > Acked-by: Jiri Olsa <jolsa@kernel.org>

Acked-by: Ian Rogers <irogers@google.com>

Arnaldo, I think this got overlooked. Thanks,

Ian

> > thanks,
> > jirka
> >
> > > ---
> > >  tools/perf/util/annotate.c | 15 +++++++++++----
> > >  1 file changed, 11 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
> > > index 70de8f6b3aee..e1b075b52dce 100644
> > > --- a/tools/perf/util/annotate.c
> > > +++ b/tools/perf/util/annotate.c
> > > @@ -1627,6 +1627,7 @@ static int dso__disassemble_filename(struct dso *dso, char *filename, size_t fil
> > >       char *build_id_filename;
> > >       char *build_id_path = NULL;
> > >       char *pos;
> > > +     int len;
> > >
> > >       if (dso->symtab_type == DSO_BINARY_TYPE__KALLSYMS &&
> > >           !dso__is_kcore(dso))
> > > @@ -1655,10 +1656,16 @@ static int dso__disassemble_filename(struct dso *dso, char *filename, size_t fil
> > >       if (pos && strlen(pos) < SBUILD_ID_SIZE - 2)
> > >               dirname(build_id_path);
> > >
> > > -     if (dso__is_kcore(dso) ||
> > > -         readlink(build_id_path, linkname, sizeof(linkname)) < 0 ||
> > > -         strstr(linkname, DSO__NAME_KALLSYMS) ||
> > > -         access(filename, R_OK)) {
> > > +     if (dso__is_kcore(dso))
> > > +             goto fallback;
> > > +
> > > +     len = readlink(build_id_path, linkname, sizeof(linkname) - 1);
> > > +     if (len < 0)
> > > +             goto fallback;
> > > +
> > > +     linkname[len] = '\0';
> > > +     if (strstr(linkname, DSO__NAME_KALLSYMS) ||
> > > +             access(filename, R_OK)) {
> > >  fallback:
> > >               /*
> > >                * If we don't have build-ids or the build-id file isn't in the
> > > --
> > > 2.22.0.709.g102302147b-goog
> > >