netdev - Re: [PATCH bpf-next] selftests/bpf: fix prog_tests/uprobe

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Date:   Thu, 21 Apr 2022 09:57:29 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Artem Savkov <asavkov@...hat.com>,
        Alan Maguire <alan.maguire@...cle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next] selftests/bpf: fix prog_tests/uprobe_autoattach
 compilation error

On Thu, Apr 21, 2022 at 9:53 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 4/21/22 3:23 PM, Artem Savkov wrote:
> > I am getting the following compilation error for prog_tests/uprobe_autoattach.c
> >
> > tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c: In function ‘test_uprobe_autoattach’:
> > ./test_progs.h:209:26: error: pointer ‘mem’ may be used after ‘free’ [-Werror=use-after-free]
> >
> > mem variable is now used in one of the asserts so it shouldn't be freed right
> > away. Move free(mem) after the assert block.
>
> Looks good, but I rephrased this a bit to avoid confusion. It's false positive given we
> only compare the addresses but don't deref mem, which the compiler might not be able to
> follow in this case.
>

Great, thanks Daniel!

> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=6a12b8e20d7e72386594a9dbe7bf2d7fae3b3aa6
>
> Thanks,
> Daniel
>
> > Fixes: 1717e248014c ("selftests/bpf: Uprobe tests should verify param/return values")
> > Signed-off-by: Artem Savkov <asavkov@...hat.com>
> > ---
> >   tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c b/tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c
> > index d6003dc8cc99..35b87c7ba5be 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c
> > @@ -34,7 +34,6 @@ void test_uprobe_autoattach(void)
> >
> >       /* trigger & validate shared library u[ret]probes attached by name */
> >       mem = malloc(malloc_sz);
> > -     free(mem);
> >
> >       ASSERT_EQ(skel->bss->uprobe_byname_parm1, trigger_val, "check_uprobe_byname_parm1");
> >       ASSERT_EQ(skel->bss->uprobe_byname_ran, 1, "check_uprobe_byname_ran");
> > @@ -44,6 +43,8 @@ void test_uprobe_autoattach(void)
> >       ASSERT_EQ(skel->bss->uprobe_byname2_ran, 3, "check_uprobe_byname2_ran");
> >       ASSERT_EQ(skel->bss->uretprobe_byname2_rc, mem, "check_uretprobe_byname2_rc");
> >       ASSERT_EQ(skel->bss->uretprobe_byname2_ran, 4, "check_uretprobe_byname2_ran");
> > +
> > +     free(mem);
> >   cleanup:
> >       test_uprobe_autoattach__destroy(skel);
> >   }
> >
>