Re: [syzbot] linux-next test error: WARNING in set_peer

Kees Cook
2022-09-14T00:55:46Z

On Tue, Sep 13, 2022 at 12:51:42PM -0700, syzbot wrote:
> memcpy: detected field-spanning write (size 28) of single field "&endpoint.addr" at drivers/net/wireguard/netlink.c:446 (size 16)

This is one way to fix it:

diff --git a/drivers/net/wireguard/netlink.c b/drivers/net/wireguard/netlink.c
index 0c0644e762e5..dbbeba216530 100644
--- a/drivers/net/wireguard/netlink.c
+++ b/drivers/net/wireguard/netlink.c
@@ -434,16 +434,16 @@ static int set_peer(struct wg_device *wg, struct nlattr **attrs)
}

if (attrs[WGPEER_A_ENDPOINT]) {
- struct sockaddr *addr = nla_data(attrs[WGPEER_A_ENDPOINT]);
+ struct endpoint *raw = nla_data(attrs[WGPEER_A_ENDPOINT]);
size_t len = nla_len(attrs[WGPEER_A_ENDPOINT]);

if ((len == sizeof(struct sockaddr_in) &&
- addr->sa_family == AF_INET) ||
+ raw->addr.sa_family == AF_INET) ||
(len == sizeof(struct sockaddr_in6) &&
- addr->sa_family == AF_INET6)) {
+ raw->addr.sa_family == AF_INET6)) {
struct endpoint endpoint = { { { 0 } } };

- memcpy(&endpoint.addr, addr, len);
+ memcpy(&endpoint.addrs, &raw->addrs, len);
wg_socket_set_peer_endpoint(peer, &endpoint);
}
}
diff --git a/drivers/net/wireguard/peer.h b/drivers/net/wireguard/peer.h
index 76e4d3128ad4..4fbe7940828b 100644
--- a/drivers/net/wireguard/peer.h
+++ b/drivers/net/wireguard/peer.h
@@ -19,11 +19,13 @@
struct wg_device;

struct endpoint {
- union {
- struct sockaddr addr;
- struct sockaddr_in addr4;
- struct sockaddr_in6 addr6;
- };
+ struct_group(addrs,
+ union {
+ struct sockaddr addr;
+ struct sockaddr_in addr4;
+ struct sockaddr_in6 addr6;
+ };
+ );
union {
struct {
struct in_addr src4;

diffoscope shows the bounds check gets updated to the full union size:
│ - cmp $0x11,%edx
│ + cmp $0x1d,%edx

and the field name changes in the warning:
$ strings clang/drivers/net/wireguard/netlink.o.after | grep ^field
field "&endpoint.addrs" at drivers/net/wireguard/netlink.c:446

--
Kees Cook