netdev - Re: [PATCH bpf-next] libbpf: silence GCC8 warning about string truncation

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Date:   Wed, 24 Jul 2019 15:27:38 +0200
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        kernel-team@...com, Magnus Karlsson <magnus.karlsson@...el.com>
Subject: Re: [PATCH bpf-next] libbpf: silence GCC8 warning about string truncation

On Wed, Jul 24, 2019 at 4:33 AM Andrii Nakryiko <andriin@...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@...el.com>

> Cc: Magnus Karlsson <magnus.karlsson@...el.com>
> Signed-off-by: Andrii Nakryiko <andriin@...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
>