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

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Date:   Fri, 12 Jul 2019 19:31:25 +0200
From:   Krzesimir Nowak <krzesimir@...volk.io>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        Alban Crequy <alban@...volk.io>,
        Iago López Galeiras <iago@...volk.io>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        xdp-newbies@...r.kernel.org
Subject: Re: [bpf-next v3 02/12] selftests/bpf: Avoid a clobbering of errno

On Fri, Jul 12, 2019 at 2:59 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Jul 11, 2019 at 5:04 AM Krzesimir Nowak <krzesimir@...volk.io> wrote:
> >
> > On Thu, Jul 11, 2019 at 1:52 AM Andrii Nakryiko
> > <andrii.nakryiko@...il.com> wrote:
> > >
> > > On Mon, Jul 8, 2019 at 3:42 PM Krzesimir Nowak <krzesimir@...volk.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@...earbox.net>
> > > > Fixes: 832c6f2c29ec ("bpf: test make sure to run unpriv test cases in test_verifier")
> > > > Signed-off-by: Krzesimir Nowak <krzesimir@...volk.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