linux-kernel - Re: [PATCH bpf-next] libbpf: poison strlcpy()

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Date:   Wed, 8 Mar 2023 16:32:52 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Boris Burkov <boris@....io>
Cc:     Rong Tao <rtoax@...mail.com>, andrii@...nel.org, rongtao@...tc.cn,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>,
        "open list:BPF [LIBRARY] (libbpf)" <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] libbpf: poison strlcpy()

On Wed, Mar 8, 2023 at 4:30 PM Boris Burkov <boris@....io> wrote:
>
> On Thu, Jan 05, 2023 at 10:47:15AM -0800, sdf@...gle.com wrote:
> > On 01/05, Rong Tao wrote:
> > > From: Rong Tao <rongtao@...tc.cn>
> >
> > > Since commit 9fc205b413b3("libbpf: Add sane strncpy alternative and use
> > > it internally") introduce libbpf_strlcpy(), thus add strlcpy() to a poison
> > > list to prevent accidental use of it.
> >
> > > Signed-off-by: Rong Tao <rongtao@...tc.cn>
> >
> > Acked-by: Stanislav Fomichev <sdf@...gle.com>
> >
> > > ---
> > >   tools/lib/bpf/libbpf_internal.h | 4 ++--
> > >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > > diff --git a/tools/lib/bpf/libbpf_internal.h
> > > b/tools/lib/bpf/libbpf_internal.h
> > > index 377642ff51fc..2d26ded383ca 100644
> > > --- a/tools/lib/bpf/libbpf_internal.h
> > > +++ b/tools/lib/bpf/libbpf_internal.h
> > > @@ -20,8 +20,8 @@
> > >   /* make sure libbpf doesn't use kernel-only integer typedefs */
> > >   #pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64
> >
> > > -/* prevent accidental re-addition of reallocarray() */
> > > -#pragma GCC poison reallocarray
> > > +/* prevent accidental re-addition of reallocarray()/strlcpy() */
> > > +#pragma GCC poison reallocarray strlcpy
>
> On my musl system, I believe this broke compilation, as string.h defines
> strlcpy, and is included after this poisoning when compiling strset.c
>
> FWIW, I could work around it by adding
> #include <string.h>
> above
> #include <libbpf_internal.h>
> in strset.c, since the poison doesn't apply to symbols that existed
> before it ran, but this feels like a kludge, and not in the spirit of
> the original poisoning patch..
>
> I'm curious what the proper workaround should be for a libc that defines
> strlcpy.

Let's move this discussion into [0]? There is a similar issue for
uclibc it seems.

0: https://lore.kernel.org/bpf/CAKH8qBshq-J2H+Bo1xA=FzAJ6x_mo5yfW6oYjQ_u1QwLJ5CDog@mail.gmail.com/T/#t

> Thanks,
> Boris
>
> >
> > >   #include "libbpf.h"
> > >   #include "btf.h"
> > > --
> > > 2.39.0
> >