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From: Magnus Karlsson <magnus.karlsson@gmail.com>
To: Andrii Nakryiko <andriin@fb.com>
Cc: bpf <bpf@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	kernel-team@fb.com, Magnus Karlsson <magnus.karlsson@intel.com>
Subject: Re: [PATCH bpf-next] libbpf: silence GCC8 warning about string truncation
Date: Wed, 24 Jul 2019 15:27:38 +0200	[thread overview]
Message-ID: <CAJ8uoz17j9hzDFaYXRmLc0ziC5mwRCAYvvjmCkfUKHbMtcAwcQ@mail.gmail.com> (raw)
In-Reply-To: <20190723220127.1815913-1-andriin@fb.com>

On Wed, Jul 24, 2019 at 4:33 AM Andrii Nakryiko <andriin@fb.com> wrote:
>
> Despite a proper NULL-termination after strncpy(..., ..., IFNAMSIZ - 1),
> GCC8 still complains about *expected* string truncation:
>
>   xsk.c:330:2: error: 'strncpy' output may be truncated copying 15 bytes
>   from a string of length 15 [-Werror=stringop-truncation]
>     strncpy(ifr.ifr_name, xsk->ifname, IFNAMSIZ - 1);
>
> This patch gets rid of the issue altogether by using memcpy instead.
> There is no performance regression, as strncpy will still copy and fill
> all of the bytes anyway.

Let us make GCC8 happy then :-). Thanks Andrii.

Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> ---
>  tools/lib/bpf/xsk.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> index 5007b5d4fd2c..65f5dd556f99 100644
> --- a/tools/lib/bpf/xsk.c
> +++ b/tools/lib/bpf/xsk.c
> @@ -327,7 +327,7 @@ static int xsk_get_max_queues(struct xsk_socket *xsk)
>
>         channels.cmd = ETHTOOL_GCHANNELS;
>         ifr.ifr_data = (void *)&channels;
> -       strncpy(ifr.ifr_name, xsk->ifname, IFNAMSIZ - 1);
> +       memcpy(ifr.ifr_name, xsk->ifname, IFNAMSIZ - 1);
>         ifr.ifr_name[IFNAMSIZ - 1] = '\0';
>         err = ioctl(fd, SIOCETHTOOL, &ifr);
>         if (err && errno != EOPNOTSUPP) {
> @@ -517,7 +517,7 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
>                 err = -errno;
>                 goto out_socket;
>         }
> -       strncpy(xsk->ifname, ifname, IFNAMSIZ - 1);
> +       memcpy(xsk->ifname, ifname, IFNAMSIZ - 1);
>         xsk->ifname[IFNAMSIZ - 1] = '\0';
>
>         err = xsk_set_xdp_socket_config(&xsk->config, usr_config);
> --
> 2.17.1
>

  reply	other threads:[~2019-07-24 13:27 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-23 22:01 [PATCH bpf-next] libbpf: silence GCC8 warning about string truncation Andrii Nakryiko
2019-07-24 13:27 ` Magnus Karlsson [this message]
2019-07-24 20:43 ` Song Liu

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