libbpf: fix GCC8 warning for strncpy

GCC8 started emitting warning about using strncpy with number of bytes
exactly equal destination size, which is generally unsafe, as can lead
to non-zero terminated string being copied. Use IFNAMSIZ - 1 as number
of bytes to ensure name is always zero-terminated.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Cc: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index bf15a80..b337402 100644 (file)
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -327,7 +327,8 @@ 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);
+       strncpy(ifr.ifr_name, xsk->ifname, IFNAMSIZ - 1);
+       ifr.ifr_name[IFNAMSIZ - 1] = '\0';
        err = ioctl(fd, SIOCETHTOOL, &ifr);
        if (err && errno != EOPNOTSUPP) {
                ret = -errno;