From 3885d68d8bfe0f830c4a00fef82911f8964a40b5 Mon Sep 17 00:00:00 2001 From: Duncan Roe Date: Sun, 26 Nov 2023 12:53:52 +1100 Subject: src: Add nfq_nlmsg_put2() - user specifies header flags Enable mnl programs to get an explicit acknowledgement of whether a configuration request has been accepted. (nfnl programs do this already). Signed-off-by: Duncan Roe Signed-off-by: Pablo Neira Ayuso --- include/libnetfilter_queue/libnetfilter_queue.h | 1 + src/nlmsg.c | 58 ++++++++++++++++++++++++- 2 files changed, 58 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..39fd12d 100644 --- a/src/nlmsg.c +++ b/src/nlmsg.c @@ -309,10 +309,66 @@ 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 - Set up a netlink header with user-specified flags + * in a memory buffer + * \param *buf Pointer to memory buffer + * \param type One of NFQNL_MSG_CONFIG, NFQNL_MSG_VERDICT + * or NFQNL_MSG_VERDICT_BATCH + * \param queue_num Queue number + * \param flags additional NLM_F_xxx flags to put in message header. These are + * defined in /usr/include/linux/netlink.h. nfq_nlmsg_put2() always + * sets NLM_F_REQUEST + * \returns Pointer to netlink header + * + * For most applications, the only sensible flag will be NLM_F_ACK. + * Use it to get an explicit acknowledgment from the kernel, e.g. + * attempt to configure NFQA_CFG_F_SECCTX on a kernel not supporting + * CONFIG_NETWORK_SECMARK. + * \n + * The kernel always sends a message in response to a failed command. + * NLM_F_ACK instructs the kernel to also send a message in response + * to a successful command. + * \n + * This code snippet demonstrates reading these responses: + * \verbatim + char buf[MNL_SOCKET_BUFFER_SIZE]; + + nlh = nfq_nlmsg_put2(buf, 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, buf, sizeof buf); + if (ret == -1) { + perror("mnl_socket_recvfrom"); + exit(EXIT_FAILURE); + } + + ret = mnl_cb_run(buf, ret, 0, portid, NULL, NULL); + if (ret == -1) + fprintf(stderr, "This kernel version does not allow to " + "retrieve security context.\n"); +\endverbatim + * + */ + +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; -- cgit v1.2.3