To avoid a copy, the new code takes advantage of the fact that the netfilter
netlink queue never returns multipart messages.
This means that the buffer space following that callback data is available for
packet expansion when mangling.
nfq_cb_run() is a new nfq-specific callback runqueue for netlink messages.
The principal function of nfq_cb_run() is to pass to the called function what is
the length of free space after the packet.
As a side benefit, nfq_cb_run() also gives the called function a pointer to a
zeroised struct pkt_buff, avoiding the malloc / free that was previously needed.
nfq_cb_t is a new typedef for the function called by nfq_cb_run()
[c.f. mnl_cb_t / mnl_cb_run].
No doxygen documentation update yet -
will do once function prototypes are agreed.
In the meantime, examples/nf-queue.c is updated to demonstrate the new API.
Signed-off-by: Duncan Roe <duncan_roe@xxxxxxxxxxxxxxx>
---
v2: Pass saved vars in a struct rather than use (slower) thread-local
v3: Rebase to master commit c3bada27
examples/nf-queue.c | 22 ++++++-
include/libnetfilter_queue/Makefile.am | 1 +
include/libnetfilter_queue/callback.h | 11 ++++
include/libnetfilter_queue/pktbuff.h | 2 +
src/Makefile.am | 1 +
src/extra/callback.c | 60 +++++++++++++++++++
src/extra/pktbuff.c | 80 ++++++++++++++++++--------
7 files changed, 149 insertions(+), 28 deletions(-)
create mode 100644 include/libnetfilter_queue/callback.h
create mode 100644 src/extra/callback.c
diff --git a/examples/nf-queue.c b/examples/nf-queue.c
index 3da2c24..15c0d77 100644
--- a/examples/nf-queue.c
+++ b/examples/nf-queue.c
@@ -13,6 +13,8 @@
#include <linux/types.h>
#include <linux/netfilter/nfnetlink_queue.h>
+#include <libnetfilter_queue/pktbuff.h>
+#include <libnetfilter_queue/callback.h>
#include <libnetfilter_queue/libnetfilter_queue.h>
/* NFQA_CT requires CTA_* attributes defined in nfnetlink_conntrack.h */
@@ -46,13 +48,17 @@ nfq_send_verdict(int queue_num, uint32_t id)
}
}
-static int queue_cb(const struct nlmsghdr *nlh, void *data)
+static int queue_cb(const struct nlmsghdr *nlh, void *data,
+ struct pkt_buff *supplied_pktb, size_t supplied_extra)
{
struct nfqnl_msg_packet_hdr *ph = NULL;
struct nlattr *attr[NFQA_MAX+1] = {};
+ struct pkt_buff *pktb;
uint32_t id = 0, skbinfo;
struct nfgenmsg *nfg;
+ uint8_t *payload;
uint16_t plen;
+ int i;
if (nfq_nlmsg_parse(nlh, attr) < 0) {
perror("problems parsing");
@@ -69,7 +75,10 @@ static int queue_cb(const struct nlmsghdr *nlh, void *data)
ph = mnl_attr_get_payload(attr[NFQA_PACKET_HDR]);
plen = mnl_attr_get_payload_len(attr[NFQA_PAYLOAD]);
- /* void *payload = mnl_attr_get_payload(attr[NFQA_PAYLOAD]); */
+ payload = mnl_attr_get_payload(attr[NFQA_PAYLOAD]);
+
+ pktb = pktb_populate(supplied_pktb, AF_INET, payload, plen,
+ supplied_extra);
skbinfo = attr[NFQA_SKB_INFO] ? ntohl(mnl_attr_get_u32(attr[NFQA_SKB_INFO])) : 0;
@@ -115,6 +124,13 @@ static int queue_cb(const struct nlmsghdr *nlh, void *data)
printf(", checksum not ready");
puts(")");
+ printf("payload (len=%d) [", plen);
+
+ for (i = 0; i < pktb_len(pktb); i++)
+ printf("%02x", payload[i]);
+
+ printf("]\n");
+
nfq_send_verdict(ntohs(nfg->res_id), id);
return MNL_CB_OK;
@@ -186,7 +202,7 @@ int main(int argc, char *argv[])
exit(EXIT_FAILURE);
}
- ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);
+ ret = nfq_cb_run(buf, ret, sizeof_buf, portid, queue_cb, NULL);
if (ret < 0){
perror("mnl_cb_run");
exit(EXIT_FAILURE);
diff --git a/include/libnetfilter_queue/Makefile.am b/include/libnetfilter_queue/Makefile.am
index e436bab..ed6524b 100644
--- a/include/libnetfilter_queue/Makefile.am
+++ b/include/libnetfilter_queue/Makefile.am
@@ -5,4 +5,5 @@ pkginclude_HEADERS = libnetfilter_queue.h \
libnetfilter_queue_ipv6.h \
libnetfilter_queue_tcp.h \
libnetfilter_queue_udp.h \
+ callback.h \
pktbuff.h
diff --git a/include/libnetfilter_queue/callback.h b/include/libnetfilter_queue/callback.h
new file mode 100644
index 0000000..27bfe31
--- /dev/null
+++ b/include/libnetfilter_queue/callback.h
@@ -0,0 +1,11 @@
+#ifndef _LIBNETFILTER_QUEUE_CALLBACK_H_
+#define _LIBNETFILTER_QUEUE_CALLBACK_H_
+
+struct nlattr;
+struct pkt_buff;
+
+typedef int (*nfq_cb_t)(const struct nlmsghdr *nlh, void *data, struct pkt_buff *pktb, size_t extra);
+
+int nfq_cb_run(const void *buf, size_t buflen, size_t bufcap, unsigned int portid, nfq_cb_t cb_data, void *data);
+
+#endif
diff --git a/include/libnetfilter_queue/pktbuff.h b/include/libnetfilter_queue/pktbuff.h
index 42bc153..33829cc 100644
--- a/include/libnetfilter_queue/pktbuff.h
+++ b/include/libnetfilter_queue/pktbuff.h
@@ -6,6 +6,8 @@ struct pkt_buff;
struct pkt_buff *pktb_alloc(int family, void *data, size_t len, size_t extra);
void pktb_free(struct pkt_buff *pktb);
+struct pkt_buff *pktb_populate(struct pkt_buff *pktb, int family, void *data, size_t len, size_t extra);
+
uint8_t *pktb_data(struct pkt_buff *pktb);
uint32_t pktb_len(struct pkt_buff *pktb);
diff --git a/src/Makefile.am b/src/Makefile.am
index 079853e..376bc45 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -31,6 +31,7 @@ libnetfilter_queue_la_LDFLAGS = -Wc,-nostartfiles \
libnetfilter_queue_la_SOURCES = libnetfilter_queue.c \
nlmsg.c \
extra/checksum.c \
+ extra/callback.c \
extra/icmp.c \
extra/ipv6.c \
extra/tcp.c \
diff --git a/src/extra/callback.c b/src/extra/callback.c
new file mode 100644
index 0000000..2d67848
--- /dev/null
+++ b/src/extra/callback.c
@@ -0,0 +1,60 @@
+/*
+ * (C) 2021 by Duncan Roe <duncan_roe@xxxxxxxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <libmnl/libmnl.h>
+#include <linux/netlink.h>
+#include <libnetfilter_queue/callback.h>
+#include <libnetfilter_queue/libnetfilter_queue.h>
+#include "internal.h"
+
+/* ---------------------------------------------------------------------- */
+/* It would be less code to have local_cb() declared within nfq_cb_run(). */
+/* gcc is fine with that; unfortunately clang 8.0.1 is not. */
+/* Lexical scoping would have given access to the 3 outer stack variables */
+/* needed by local_cb(); absent that, pass them down through the data arg */
+/* ---------------------------------------------------------------------- */
+
+typedef struct qwerty
+{
+ nfq_cb_t cb_func;
+ size_t buflen;
+ size_t bufcap;
+ void *data;
+} werty;
+
+static int local_cb(const struct nlmsghdr *nlh, void *data)
+{
+ struct pkt_buff pktb_instance = { };
+ werty *w = (werty *)data;
+
+ return w->cb_func(nlh, w->data, &pktb_instance, w->bufcap - w->buflen);
+}
+
+EXPORT_SYMBOL int nfq_cb_run(const void *buf, size_t buflen, size_t bufcap,
+ unsigned int portid, nfq_cb_t cb_func, void *data)
+{
+ const struct nlmsghdr *nlh = buf;
+ werty wert;
+
+ wert.cb_func = cb_func;
+ wert.bufcap = bufcap;
+ wert.buflen = buflen;
+ wert.data = data;
+
+ /* Verify not multi-part */
+ if (nlh->nlmsg_flags & NLM_F_MULTI) {
+ errno = E2BIG;
+ return MNL_CB_ERROR;
+ }
+
+
+ return mnl_cb_run(buf, buflen, 0, portid, local_cb, &wert);
+}
diff --git a/src/extra/pktbuff.c b/src/extra/pktbuff.c
index 005172c..df23335 100644
--- a/src/extra/pktbuff.c
+++ b/src/extra/pktbuff.c
@@ -19,6 +19,8 @@
#include <netinet/tcp.h>
#include "internal.h"
+#include <libnetfilter_queue/pktbuff.h> /* I.e. local copy */
+ /* (to verify prototypes) */
/**
* \defgroup pktbuff User-space network packet buffer
@@ -67,6 +60,15 @@ static int __pktb_setup(int family, struct pkt_buff *pktb)
return 0;
}
+static void pktb_setup_metadata(struct pkt_buff *pktb, void *pkt_data,
+ size_t len, size_t extra)
+{
+ pktb->len = len;
+ pktb->data_len = len + extra;
+
+ pktb->data = pkt_data;
+}
+
/**
* pktb_alloc - allocate a new packet buffer
* \param family Indicate what family. Currently supported families are
@@ -100,10 +102,7 @@ struct pkt_buff *pktb_alloc(int family, void *data, size_t len, size_t extra)
pkt_data = (uint8_t *)pktb + sizeof(struct pkt_buff);
memcpy(pkt_data, data, len);
- pktb->len = len;
- pktb->data_len = len + extra;
-
- pktb->data = pkt_data;
+ pktb_setup_metadata(pktb, pkt_data, len, extra);
if (__pktb_setup(family, pktb) < 0) {
free(pktb);
@@ -113,6 +112,17 @@ struct pkt_buff *pktb_alloc(int family, void *data, size_t len, size_t extra)
return pktb;
}
+EXPORT_SYMBOL
+struct pkt_buff *pktb_populate(struct pkt_buff *pktb, int family, void *data,
+ size_t len, size_t extra)
+{
+ pktb_setup_metadata(pktb, data, len, extra);
+ if (__pktb_setup(family, pktb) < 0)
+ pktb = NULL;
+ return pktb;
+}
+
+
/**
* pktb_data - get pointer to network packet
* \param pktb Pointer to userspace packet buffer
