[PATCH AUTOSEL 5.2 042/123] libbpf: silence GCC8 warning about string truncation

Sasha Levin
2019-08-14T02:12:32Z

From: Andrii Nakryiko <andriin@fb.com>

[ Upstream commit cb8ffde5694ae5fffb456eae932aac442aa3a207 ]

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>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 8e03b65830da0..fa948c5445ecf 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -336,7 +336,7 @@ 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) {
@@ -561,7 +561,7 @@ 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);
--
2.20.1