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 5da0da5..e2ae82e 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 9ebdf32..d73091f 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));
        }