netlink: remove the flex array from struct nlmsghdr

I've added a flex array to struct nlmsghdr in
commit 738136a0e375 ("netlink: split up copies in the ack construction")
to allow accessing the data easily. It leads to warnings with clang,
if user space wraps this structure into another struct and the flex
array is not at the end of the container.

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/all/20221114023927.GA685@u2004-local/
Link: https://lore.kernel.org/r/20221118033903.1651026-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index 5da0da59bf010099e7714447738e68d9650a1565..e2ae82e3f9f7187d12ad6d78b6875cfccce878cd 100644 (file)
--- a/include/uapi/linux/netlink.h
+++ b/include/uapi/linux/netlink.h
@@ -48,7 +48,6 @@ struct sockaddr_nl {
  * @nlmsg_flags: Additional flags
  * @nlmsg_seq:   Sequence number
  * @nlmsg_pid:   Sending process port ID
- * @nlmsg_data:  Message payload
  */
 struct nlmsghdr {
        __u32           nlmsg_len;
@@ -56,7 +55,6 @@ struct nlmsghdr {
        __u16           nlmsg_flags;
        __u32           nlmsg_seq;
        __u32           nlmsg_pid;
-       __u8            nlmsg_data[];
 };
 
 /* Flags values */

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 9ebdf3262015cb0c4b5bc0298ff24ed1ef9ac11c..d73091f6bb0f349858d800b8489ae6912c3a885a 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2514,7 +2514,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
                if (!nlmsg_append(skb, nlmsg_len(nlh)))
                        goto err_bad_put;
 
-               memcpy(errmsg->msg.nlmsg_data, nlh->nlmsg_data,
+               memcpy(nlmsg_data(&errmsg->msg), nlmsg_data(nlh),
                       nlmsg_len(nlh));
        }