In preparation for FORTIFY_SOURCE performing compile-time and run-time field bounds checking for memcpy(), memmove(), and memset(), avoid intentionally writing across neighboring fields.
Add a flexible array member to mark the end of struct nlmsghdr, and split the memcpy() to avoid false positive memcpy() warning:
memcpy: detected field-spanning write (size 32) of single field (size 16)
Signed-off-by: Kees Cook keescook@chromium.org --- include/uapi/linux/netlink.h | 1 + net/netlink/af_netlink.c | 4 +++- 2 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h index 4c0cde075c27..ddeaa748df5e 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 contents[]; };
/* Flags values */ diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 24b7cf447bc5..f2dd99e96822 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2447,7 +2447,9 @@ 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)); + memcpy(&errmsg->msg, nlh, sizeof(*nlh)); + if (payload > sizeof(*errmsg)) + memcpy(errmsg->msg.contents, nlh->contents, nlh->nlmsg_len - sizeof(*nlh));
if (nlk_has_extack && extack) { if (extack->_msg) {