netdev - Re: [PATCH bpf] tools: bpftool: close prog FD before exit on showing a single program

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Message-ID: <CAEf4BzYL-pJ79nKywsAH1b2S-EP_4SUZY5jS2wzYJ32pywsyrw@mail.gmail.com>
Date:   Thu, 15 Aug 2019 11:05:16 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Quentin Monnet <quentin.monnet@...ronome.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com
Subject: Re: [PATCH bpf] tools: bpftool: close prog FD before exit on showing
 a single program

On Thu, Aug 15, 2019 at 10:30 AM Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
> On Thu, 15 Aug 2019 10:09:38 -0700, Andrii Nakryiko wrote:
> > On Thu, Aug 15, 2019 at 7:24 AM Quentin Monnet wrote:
> > > When showing metadata about a single program by invoking
> > > "bpftool prog show PROG", the file descriptor referring to the program
> > > is not closed before returning from the function. Let's close it.
> > >
> > > Fixes: 71bb428fe2c1 ("tools: bpf: add bpftool")
> > > Signed-off-by: Quentin Monnet <quentin.monnet@...ronome.com>
> > > Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> > > ---
> > >  tools/bpf/bpftool/prog.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> > > index 66f04a4846a5..43fdbbfe41bb 100644
> > > --- a/tools/bpf/bpftool/prog.c
> > > +++ b/tools/bpf/bpftool/prog.c
> > > @@ -363,7 +363,9 @@ static int do_show(int argc, char **argv)
> > >                 if (fd < 0)
> > >                         return -1;
> > >
> > > -               return show_prog(fd);
> > > +               err = show_prog(fd);
> > > +               close(fd);
> > > +               return err;
> >
> > There is a similar problem few lines above for special case of argc ==
> > 2, which you didn't fix.
>
> This is the special argc == 2 case.

Yep, you are right, the other one already does this.

>
> > Would it be better to make show_prog(fd) close provided fd instead or
> > is it used in some other context where FD should live longer (I
> > haven't checked, sorry)?
>
> I think it used to close that's how the bug crept in. Other than the bug
> it's fine the way it is.

So are you saying that show_prog() should or should not close FD?