Re: [PATCH v2 2/3] perf trace: avoid garbage when not printing a syscall's arguments

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Fri, Nov 08, 2024 at 08:21:30AM -0800, Howard Chu wrote:
> Hello,
> 
> This patch solves the garbage output problem I got, and your test can be run.

I'm taking this as a Tested-by you, ok?

- Arnaldo
 
> Thanks,
> Howard
> 
> On Thu, Nov 7, 2024 at 3:21 PM Benjamin Peterson <benjamin@engflow.com> wrote:
> >
> > syscall__scnprintf_args may not place anything in the output buffer
> > (e.g., because the arguments are all zero). If that happened in
> > trace__fprintf_sys_enter, its fprintf would receive an unitialized
> > buffer leading to garbage output.
> >
> > Fix the problem by passing the (possibly zero) bounds of the argument
> > buffer to the output fprintf.
> >
> > Fixes: a98392bb1e169 ("perf trace: Use beautifiers on syscalls:sys_enter_ handlers")
> > Signed-off-by: Benjamin Peterson <benjamin@engflow.com>
> > ---
> >  tools/perf/builtin-trace.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> > index f6179b13b8b4..28f61d10a2f8 100644
> > --- a/tools/perf/builtin-trace.c
> > +++ b/tools/perf/builtin-trace.c
> > @@ -2702,6 +2702,7 @@ static int trace__fprintf_sys_enter(struct trace *trace, struct evsel *evsel,
> >         char msg[1024];
> >         void *args, *augmented_args = NULL;
> >         int augmented_args_size;
> > +       size_t printed = 0;
> >
> >         if (sc == NULL)
> >                 return -1;
> > @@ -2717,8 +2718,8 @@ static int trace__fprintf_sys_enter(struct trace *trace, struct evsel *evsel,
> >
> >         args = perf_evsel__sc_tp_ptr(evsel, args, sample);
> >         augmented_args = syscall__augmented_args(sc, sample, &augmented_args_size, trace->raw_augmented_syscalls_args_size);
> > -       syscall__scnprintf_args(sc, msg, sizeof(msg), args, augmented_args, augmented_args_size, trace, thread);
> > -       fprintf(trace->output, "%s", msg);
> > +       printed += syscall__scnprintf_args(sc, msg, sizeof(msg), args, augmented_args, augmented_args_size, trace, thread);
> > +       fprintf(trace->output, "%.*s", (int)printed, msg);
> >         err = 0;
> >  out_put:
> >         thread__put(thread);
> > --
> > 2.39.5
> >
> >