[PATCH v2 bpf] libbpf: silence GCC8 warning about string truncation

[PATCH v2 bpf] 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.

v1->v2:
- rebase against bpf tree.

Cc: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Song Liu <songliubraving@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 e02025bbe36d..680e63066cf3 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -326,7 +326,7 @@ static int xsk_get_max_queues(struct xsk_socket *xsk)
 		return -errno;
 
 	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) {
@@ -516,7 +516,7 @@ 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 v2 bpf] libbpf: silence GCC8 warning about string truncation

[Alexei Starovoitov]

On Wed, Jul 24, 2019 at 10:46 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.
>
> v1->v2:
> - rebase against bpf tree.
>
> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
> Acked-by: Song Liu <songliubraving@fb.com>

Applied. Thanks