From: Kees Cook <keescook@xxxxxxxxxxxx> commit 710d21fdff9a98d621cd4e64167f3ef8af4e2fd1 upstream. In preparation for FORTIFY_SOURCE doing bounds-check on memcpy(), switch from __nlmsg_put to nlmsg_put(), and explain the bounds check for dealing with the memcpy() across a composite flexible array struct. Avoids this future run-time warning: memcpy: detected field-spanning write (size 32) of single field "&errmsg->msg" at net/netlink/af_netlink.c:2447 (size 16) Cc: Jakub Kicinski <kuba@xxxxxxxxxx> Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> Cc: Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxx> Cc: Florian Westphal <fw@xxxxxxxxx> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> Cc: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: Paolo Abeni <pabeni@xxxxxxxxxx> Cc: syzbot <syzkaller@xxxxxxxxxxxxxxxx> Cc: netfilter-devel@xxxxxxxxxxxxxxx Cc: coreteam@xxxxxxxxxxxxx Cc: netdev@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220901071336.1418572-1-keescook@xxxxxxxxxxxx Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/netfilter/ipset/ip_set_core.c | 8 +++++--- net/netlink/af_netlink.c | 8 +++++--- 2 files changed, 10 insertions(+), 6 deletions(-) --- a/net/netfilter/ipset/ip_set_core.c +++ b/net/netfilter/ipset/ip_set_core.c @@ -1719,11 +1719,13 @@ call_ad(struct net *net, struct sock *ct skb2 = nlmsg_new(payload, GFP_KERNEL); if (!skb2) return -ENOMEM; - rep = __nlmsg_put(skb2, NETLINK_CB(skb).portid, - nlh->nlmsg_seq, NLMSG_ERROR, payload, 0); + rep = nlmsg_put(skb2, NETLINK_CB(skb).portid, + nlh->nlmsg_seq, NLMSG_ERROR, payload, 0); errmsg = nlmsg_data(rep); errmsg->error = ret; - memcpy(&errmsg->msg, nlh, nlh->nlmsg_len); + unsafe_memcpy(&errmsg->msg, nlh, nlh->nlmsg_len, + /* Bounds checked by the skb layer. */); + cmdattr = (void *)&errmsg->msg + min_len; ret = nla_parse(cda, IPSET_ATTR_CMD_MAX, cmdattr, --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2440,11 +2440,13 @@ void netlink_ack(struct sk_buff *in_skb, return; } - rep = __nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq, - NLMSG_ERROR, payload, flags); + rep = nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq, + NLMSG_ERROR, payload, flags); errmsg = nlmsg_data(rep); errmsg->error = err; - memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh)); + unsafe_memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) + ? nlh->nlmsg_len : sizeof(*nlh), + /* Bounds checked by the skb layer. */); if (nlk_has_extack && extack) { if (extack->_msg) {
