In preparation for run-time memcpy() bounds checking, split the nlmsg copying for error messages (which crosses a previous unspecified flexible array boundary) in half. Avoids the future run-time warning: memcpy: detected field-spanning write (size 32) of single field "&errmsg->msg" (size 16) Creates an explicit flexible array at the end of nlmsghdr for the payload, named "nlmsg_payload". There is no impact on UAPI; the sizeof(struct nlmsghdr) does not change, but now the compiler can better reason about where things are being copied. Fixed-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/lkml/d7251d92-150b-5346-6237-52afc154bb00@xxxxxxxxxxxxxxxxxx Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> Cc: Jakub Kicinski <kuba@xxxxxxxxxx> Cc: Rich Felker <dalias@xxxxxxxxxx> Cc: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: netdev@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- include/uapi/linux/netlink.h | 1 + net/netlink/af_netlink.c | 5 ++++- 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h index 855dffb4c1c3..47f9342d51bc 100644 --- a/include/uapi/linux/netlink.h +++ b/include/uapi/linux/netlink.h @@ -47,6 +47,7 @@ struct nlmsghdr { __u16 nlmsg_flags; /* Additional flags */ __u32 nlmsg_seq; /* Sequence number */ __u32 nlmsg_pid; /* Sending process port ID */ + __u8 nlmsg_payload[];/* Contents of message */ }; /* Flags values */ diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 1b5a9c2e1c29..09346aee1022 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2445,7 +2445,10 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err, NLMSG_ERROR, payload, flags); errmsg = nlmsg_data(rep); errmsg->error = err; - memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh)); + errmsg->msg = *nlh; + if (payload > sizeof(*errmsg)) + memcpy(errmsg->msg.nlmsg_payload, nlh->nlmsg_payload, + nlh->nlmsg_len - sizeof(*nlh)); if (nlk_has_extack && extack) { if (extack->_msg) { -- 2.32.0
