netdev - [PATCH v2 bpf-next] libbpf: fix GCC8 warning for strncpy

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Date:   Tue, 2 Jul 2019 08:16:20 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <andrii.nakryiko@...il.com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <ast@...com>, <daniel@...earbox.net>,
        <andriin@...com>, <magnus.karlsson@...el.com>
Subject: [PATCH v2 bpf-next] 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.

Cc: Magnus Karlsson <magnus.karlsson@...el.com>
Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/lib/bpf/xsk.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index bf15a80a37c2..b33740221b7e 100644
--- 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;
-- 
2.17.1