Re: [bpf-next v3 02/12] selftests/bpf: Avoid a clobbering of errno

From: Krzesimir Nowak <krzesimir@kinvolk.io>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: "open list" <linux-kernel@vger.kernel.org>,
	"Alban Crequy" <alban@kinvolk.io>,
	"Iago López Galeiras" <iago@kinvolk.io>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <jakub.kicinski@netronome.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Stanislav Fomichev" <sdf@google.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	xdp-newbies@vger.kernel.org
Subject: Re: [bpf-next v3 02/12] selftests/bpf: Avoid a clobbering of errno
Date: Fri, 12 Jul 2019 19:31:25 +0200	[thread overview]
Message-ID: <CAGGp+cGgwO2YEtERi7aVz7+iex3x+MzT9+2Lst1JteS9DLAc=w@mail.gmail.com> (raw)
In-Reply-To: <CAEf4Bzb-KW+p1zFcz39OSUuH0=DLFRNLa3NYT4V_-zz0Q_TJ5g@mail.gmail.com>

On Fri, Jul 12, 2019 at 2:59 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Thu, Jul 11, 2019 at 5:04 AM Krzesimir Nowak <krzesimir@kinvolk.io> wrote:
> >
> > On Thu, Jul 11, 2019 at 1:52 AM Andrii Nakryiko
> > <andrii.nakryiko@gmail.com> wrote:
> > >
> > > On Mon, Jul 8, 2019 at 3:42 PM Krzesimir Nowak <krzesimir@kinvolk.io> wrote:
> > > >
> > > > Save errno right after bpf_prog_test_run returns, so we later check
> > > > the error code actually set by bpf_prog_test_run, not by some libcap
> > > > function.
> > > >
> > > > Changes since v1:
> > > > - Fix the "Fixes:" tag to mention actual commit that introduced the
> > > >   bug
> > > >
> > > > Changes since v2:
> > > > - Move the declaration so it fits the reverse christmas tree style.
> > > >
> > > > Cc: Daniel Borkmann <daniel@iogearbox.net>
> > > > Fixes: 832c6f2c29ec ("bpf: test make sure to run unpriv test cases in test_verifier")
> > > > Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
> > > > ---
> > > >  tools/testing/selftests/bpf/test_verifier.c | 4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > > > index b8d065623ead..3fe126e0083b 100644
> > > > --- a/tools/testing/selftests/bpf/test_verifier.c
> > > > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > > > @@ -823,16 +823,18 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
> > > >         __u8 tmp[TEST_DATA_LEN << 2];
> > > >         __u32 size_tmp = sizeof(tmp);
> > > >         uint32_t retval;
> > > > +       int saved_errno;
> > > >         int err;
> > > >
> > > >         if (unpriv)
> > > >                 set_admin(true);
> > > >         err = bpf_prog_test_run(fd_prog, 1, data, size_data,
> > > >                                 tmp, &size_tmp, &retval, NULL);
> > >
> > > Given err is either 0 or -1, how about instead making err useful right
> > > here without extra variable?
> > >
> > > if (bpf_prog_test_run(...))
> > >         err = errno;
> >
> > I change it later to bpf_prog_test_run_xattr, which can also return
> > -EINVAL and then errno is not set. But this one probably should not be
>
> This is wrong. bpf_prog_test_run/bpf_prog_test_run_xattr should either
> always return -1 and set errno to actual error (like syscalls do), or
> always use return code with proper error. Give they are pretending to
> be just pure syscall, it's probably better to set errno to EINVAL and
> return -1 on invalid input args?

Yeah, this is inconsistent at best. But seems to be kind of expected?
See tools/testing/selftests/bpf/prog_tests/prog_run_xattr.c.

>
> > triggered by the test code. So not sure, probably would be better to
> > keep it as is for consistency?
> >
> > >
> > > > +       saved_errno = errno;
> > > >         if (unpriv)
> > > >                 set_admin(false);
> > > >         if (err) {
> > > > -               switch (errno) {
> > > > +               switch (saved_errno) {
> > > >                 case 524/*ENOTSUPP*/:
> > >
> > > ENOTSUPP is defined in include/linux/errno.h, is there any problem
> > > with using this in selftests?
> >
> > I just used whatever there was earlier. Seems like <linux/errno.h> is
> > not copied to tools include directory.
>
> Ok, let's leave it as is, thanks!
>
> >
> > >
> > > >                         printf("Did not run the program (not supported) ");
> > > >                         return 0;
> > > > --
> > > > 2.20.1
> > > >
> >
> >
> >
> > --
> > Kinvolk GmbH | Adalbertstr.6a, 10999 Berlin | tel: +491755589364
> > Geschäftsführer/Directors: Alban Crequy, Chris Kühl, Iago López Galeiras
> > Registergericht/Court of registration: Amtsgericht Charlottenburg
> > Registernummer/Registration number: HRB 171414 B
> > Ust-ID-Nummer/VAT ID number: DE302207000

-- 
Kinvolk GmbH | Adalbertstr.6a, 10999 Berlin | tel: +491755589364
Geschäftsführer/Directors: Alban Crequy, Chris Kühl, Iago López Galeiras
Registergericht/Court of registration: Amtsgericht Charlottenburg
Registernummer/Registration number: HRB 171414 B
Ust-ID-Nummer/VAT ID number: DE302207000