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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 >
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