[PATCH] netlink: decode NLMSG_DONE message

[Dmitry V. Levin]

On Fri, May 05, 2017 at 06:21:17PM +0800, JingPiao Chen wrote:
> * netlink.c (decode_payload): Decode NLMSG_DONE message.
> * tests/netlink_protocol.c: Add check for decoding
> of NLMSG_DONE message.
> ---
>  netlink.c                |  5 +++++
>  tests/netlink_protocol.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/netlink.c b/netlink.c
> index 16550d6..d00ff42 100644
> --- a/netlink.c
> +++ b/netlink.c
> @@ -113,6 +113,11 @@ decode_payload(struct tcb *const tcp,
>  {
>  	if (nlmsghdr->nlmsg_type == NLMSG_ERROR && len >= sizeof(int)) {
>  		decode_nlmsgerr(tcp, addr, len);
> +	} else if (nlmsghdr->nlmsg_type == NLMSG_DONE && len >= sizeof(int)) {
> +		int total_len;
> +
> +		if (!umove_or_printaddr(tcp, addr, &total_len))
> +			tprintf("%d", total_len);
>  	} else {
>  		printstrn(tcp, addr, len);
>  	}

Unlike NLMSG_ERROR, there are no universal NLMSG_DONE messages.  While
many NLMSG_DONE messages indeed have payload containing just one integer,
there are exceptions.  For example,

net/netfilter/nfnetlink_log.c:__nfulnl_send() sends struct nfgenmsg,
drivers/connector/connector.c:cn_netlink_send_mult() sends struct cn_msg,
drivers/scsi/scsi_transport_iscsi.c:iscsi_if_send_reply() sends struct iscsi_uevent,
kernel/auditfilter.c:audit_list_rules() sends struct audit_rule_data,
kernel/audit.c:audit_get_feature() sends struct audit_features,
kernel/audit.c:audit_receive_msg() sends struct audit_status, audit_sig_info,
audit_tty_status, and so on.

I suggest implementing a default decoder of NLMSG_DONE messages that
would print the integer in case of len == sizeof(int) and fall back
to  printstrn for other lengths.

When protocol specific netlink decoders are added, they could either
decode NLMSG_DONE themselves (and return true) or just return false to
fall back to default decoder.


-- 
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