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

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

[Andrii Nakryiko]

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.

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

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

[Magnus Karlsson]

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
>

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

[Song Liu]

On Tue, Jul 23, 2019 at 7:33 PM 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.
>
> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Song Liu <songliubraving@fb.com>