On Wed, Nov 15, 2023 at 10:30:11PM +1100, Duncan Roe wrote:
> Enable mnl programs to check whether a config request was accepted.
> (nfnl programs do this already).
>
> v3: force on NLM_F_REQUEST
>
> v2: take flags as an arg (Pablo request)
> Signed-off-by: Duncan Roe <duncan_roe@xxxxxxxxxxxxxxx>
> ---
> .../libnetfilter_queue/libnetfilter_queue.h | 1 +
> src/nlmsg.c | 55 ++++++++++++++++++-
> 2 files changed, 55 insertions(+), 1 deletion(-)
>
> diff --git a/include/libnetfilter_queue/libnetfilter_queue.h b/include/libnetfilter_queue/libnetfilter_queue.h
> index 3d8e444..f254984 100644
> --- a/include/libnetfilter_queue/libnetfilter_queue.h
> +++ b/include/libnetfilter_queue/libnetfilter_queue.h
> @@ -151,6 +151,7 @@ void nfq_nlmsg_verdict_put_pkt(struct nlmsghdr *nlh, const void *pkt, uint32_t p
>
> int nfq_nlmsg_parse(const struct nlmsghdr *nlh, struct nlattr **attr);
> struct nlmsghdr *nfq_nlmsg_put(char *buf, int type, uint32_t queue_num);
> +struct nlmsghdr *nfq_nlmsg_put2(char *buf, int type, uint32_t queue_num, uint16_t flags);
>
> #ifdef __cplusplus
> } /* extern "C" */
> diff --git a/src/nlmsg.c b/src/nlmsg.c
> index 5400dd7..999ccfe 100644
> --- a/src/nlmsg.c
> +++ b/src/nlmsg.c
> @@ -309,10 +309,63 @@ int nfq_nlmsg_parse(const struct nlmsghdr *nlh, struct nlattr **attr)
> */
> EXPORT_SYMBOL
> struct nlmsghdr *nfq_nlmsg_put(char *buf, int type, uint32_t queue_num)
> +{
> + return nfq_nlmsg_put2(buf, type, queue_num, 0);
> +}
> +
> +/**
> + * nfq_nlmsg_put2 - Convert memory buffer into a Netlink buffer with
> + * user-specified flags
This is setting up a netlink header in the memory buffer.
> + * \param *buf Pointer to memory buffer
> + * \param type Either NFQNL_MSG_CONFIG or NFQNL_MSG_VERDICT
> + * \param queue_num Queue number
> + * \param flags additional (to NLM_F_REQUEST) flags to put in message header,
> + * commonly NLM_F_ACK
remove NLM_F_REQUEST here.
> + * \returns Pointer to netlink message
Pointer to netlink header
> + *
> + * Use NLM_F_ACK before performing an action that might fail, e.g.
Failures are always reported.
if you set NLM_F_ACK, then you always get an acknowledgment from the
kernel, either 0 to report success or negative to report failure.
if you do not set NLM_F_ACK, then only failures are reported by the
kernel.
> + * attempt to configure NFQA_CFG_F_SECCTX on a system not runnine SELinux.
> + * \n
> + * NLM_F_ACK instructs the kernel to send a message in response
> + * to a successful command.
As I said above, this is not accurate.
> + * The kernel always sends a message in response to a failed command.
> + * \n
> + * This code snippet demonstrates reading these responses:
> + * \verbatim
> + nlh = nfq_nlmsg_put2(nltxbuf, NFQNL_MSG_CONFIG, queue_num, NLM_F_ACK);
> + mnl_attr_put_u32(nlh, NFQA_CFG_FLAGS, NFQA_CFG_F_SECCTX);
> + mnl_attr_put_u32(nlh, NFQA_CFG_MASK, NFQA_CFG_F_SECCTX);
> +
> + if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
> + perror("mnl_socket_send");
> + exit(EXIT_FAILURE);
> + }
> +
> + ret = mnl_socket_recvfrom(nl, nlrxbuf, sizeof nlrxbuf);
> + if (ret == -1) {
> + perror("mnl_socket_recvfrom");
> + exit(EXIT_FAILURE);
> + }
> +
> + ret = mnl_cb_run(nlrxbuf, ret, 0, portid, NULL, NULL);
> + if (ret == -1)
> + perror("configure NFQA_CFG_F_SECCTX");
> +\endverbatim
> + *
> + * \note
> + * The program above can continue after the error because NFQA_CFG_F_SECCTX
> + * was the only item in the preceding **mnl_socket_sendto**.
> + * If there had been other items, they would not have been actioned and it would
> + * not now be safe to proceed.
> + */
> +
> +EXPORT_SYMBOL
> +struct nlmsghdr *nfq_nlmsg_put2(char *buf, int type, uint32_t queue_num,
> + uint16_t flags)
> {
> struct nlmsghdr *nlh = mnl_nlmsg_put_header(buf);
> nlh->nlmsg_type = (NFNL_SUBSYS_QUEUE << 8) | type;
> - nlh->nlmsg_flags = NLM_F_REQUEST;
> + nlh->nlmsg_flags = NLM_F_REQUEST | flags;
>
> struct nfgenmsg *nfg = mnl_nlmsg_put_extra_header(nlh, sizeof(*nfg));
> nfg->nfgen_family = AF_UNSPEC;
> --
> 2.35.8
>
