[PATCH next] extensions: add libxt_bpf extension

[Willem de Bruijn <willemb@google.com>]

Support filtering using Linux Socket Filters
---
 extensions/libxt_bpf.c |  225 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 225 insertions(+), 0 deletions(-)
 create mode 100644 extensions/libxt_bpf.c

diff --git a/extensions/libxt_bpf.c b/extensions/libxt_bpf.c
new file mode 100644
index 0000000..4c02402
--- /dev/null
+++ b/extensions/libxt_bpf.c
@@ -0,0 +1,225 @@
+/*
+ * Xtables BPF extension
+ *
+ * Written by Willem de Bruijn (willemb@google.com)
+ * Copyright Google, Inc. 2012
+ * Licensed under the GNU General Public License version 2 (GPLv2)
+*/
+
+#include <linux/netfilter/xt_bpf.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <xtables.h>
+
+#define BCODE_FILE_MAX_LEN_B	1024
+
+enum { O_BCODE_STDIN = 0,
+       O_BCODE_FILE};
+
+static void bpf_help(void)
+{
+	printf(
+"bpf match options:\n"
+"--bytecode-file <file>	: a bpf program as generated by\n"
+"  `tcpdump -i any -ddd <expr> > file\n"
+"--bytecode <program>	: a bpf program as generated by\n"
+"  `tcpdump -i any -ddd <expr> | tr '\\n' ','`\n");
+}
+
+static const struct xt_option_entry bpf_opts[] = {
+	{.name = "bytecode", .id = O_BCODE_STDIN, .type = XTTYPE_STRING},
+	{.name = "bytecode-file", .id = O_BCODE_FILE, .type = XTTYPE_STRING},
+	XTOPT_TABLEEND,
+};
+
+/* Q: make a generic libxtables call? */
+static void bpf_resize_match_struct(struct xt_option_call *cb, int head_len,
+				    int elem_len, int num_elem)
+{
+	const int match_len = sizeof(struct xt_entry_match);
+	struct xt_entry_match *new_match;
+	unsigned long new_match_size;
+
+	new_match_size = match_len + head_len + (elem_len * num_elem);
+	new_match = malloc(new_match_size);
+	if (!new_match) {
+		xtables_error(PARAMETER_PROBLEM,
+			      "bpf: allocation failed");
+		return;
+	}
+
+	memcpy(new_match, *cb->match, match_len + head_len);
+	new_match->u.match_size = new_match_size;
+
+	free(*cb->match);
+	*cb->match = new_match;
+	cb->data = ((void *) new_match) + match_len;
+}
+
+static void bpf_parse_string(struct xt_option_call *cb, const char *bpf_program,
+			     const char separator)
+{
+	struct xt_bpf_info *bi = (void *) cb->data;
+	const char *token;
+	char sp;
+	int i;
+
+	/* parse head: length. */
+	if (sscanf(bpf_program, "%hu%c", &bi->bpf_program_num_elem, &sp) != 2 ||
+		   sp != separator)
+		xtables_error(PARAMETER_PROBLEM,
+			      "bpf: error parsing program length");
+	if (!bi->bpf_program_num_elem)
+		xtables_error(PARAMETER_PROBLEM,
+			      "bpf: illegal zero length program");
+
+	/* adjust match struct to be able to store all instructions. */
+	bpf_resize_match_struct(cb,
+				sizeof(struct xt_bpf_info),
+				sizeof(struct sock_filter),
+				bi->bpf_program_num_elem);
+	bi = cb->data;
+
+	/* parse instructions. */
+	i = 0;
+	token = bpf_program;
+	while ((token = strchr(token, separator)) && (++token)[0]) {
+		if (i >= bi->bpf_program_num_elem) {
+			xtables_error(PARAMETER_PROBLEM,
+				      "bpf: program length: parameter");
+			return;
+		}
+		if (sscanf(token, "%hu %hhu %hhu %u,",
+			   &bi->bpf_program[i].code,
+			   &bi->bpf_program[i].jt,
+			   &bi->bpf_program[i].jf,
+			   &bi->bpf_program[i].k) != 4) {
+			xtables_error(PARAMETER_PROBLEM,
+				      "bpf: error at instr %d", i);
+			return;
+		}
+		i++;
+	}
+
+	if (i != bi->bpf_program_num_elem) {
+		xtables_error(PARAMETER_PROBLEM,
+			      "bpf: program length: parsing");
+		return;
+	}
+}
+
+static void bpf_parse_file(struct xt_option_call *cb, const char *filepath)
+{
+	struct stat stats;
+	char *contents;
+	int fd, len = 0, ret;
+
+	if (access(filepath, F_OK))
+		xtables_error(PARAMETER_PROBLEM, "bpf: no such file");
+	if (access(filepath, R_OK))
+		xtables_error(PARAMETER_PROBLEM, "bpf: no read permissions");
+
+	fd = open(filepath, O_RDONLY);
+	if (fd == -1)
+		xtables_error(PARAMETER_PROBLEM, "bpf: error opening file");
+	if (fstat(fd, &stats))
+		xtables_error(PARAMETER_PROBLEM, "bpf: error reading metadata");
+	if (stats.st_size >= BCODE_FILE_MAX_LEN_B)
+		xtables_error(PARAMETER_PROBLEM, "bpf: file too large");
+
+	contents = malloc(stats.st_size + 1);
+	if (!contents)
+		xtables_error(PARAMETER_PROBLEM, "bpf: allocation failed");
+	contents[stats.st_size] = 0;
+
+	while (len < stats.st_size) {
+		ret = read(fd, contents + len, stats.st_size - len);
+		if (ret == -1) {
+			if (errno == EAGAIN)
+				continue;
+			xtables_error(PARAMETER_PROBLEM, "bpf: read failed");
+		}
+		if (!ret)
+			xtables_error(PARAMETER_PROBLEM, "bpf: unexpected EOF");
+		len += ret;
+	}
+
+	bpf_parse_string(cb, contents, '\n');
+
+	free(contents);
+	close(fd);
+}
+
+static void bpf_parse(struct xt_option_call *cb)
+{
+	xtables_option_parse(cb);
+	switch (cb->entry->id) {
+	case O_BCODE_STDIN:
+		bpf_parse_string(cb, cb->arg, ',');
+		break;
+	case O_BCODE_FILE:
+		bpf_parse_file(cb, cb->arg);
+		break;
+	default:
+		xtables_error(PARAMETER_PROBLEM, "bpf: unknown option");
+	}
+}
+
+static void bpf_print_code(const void *ip, const struct xt_entry_match *match)
+{
+	const struct xt_bpf_info *info = (void *) match->data;
+	int i;
+
+	for (i = 0; i < info->bpf_program_num_elem; i++)
+		printf("%hu %hhu %hhu %u,", info->bpf_program[i].code,
+					    info->bpf_program[i].jt,
+					    info->bpf_program[i].jf,
+					    info->bpf_program[i].k);
+}
+
+static void bpf_save(const void *ip, const struct xt_entry_match *match)
+{
+	const struct xt_bpf_info *info = (void *) match->data;
+
+	printf("bpf --bytecode %hu,", info->bpf_program_num_elem);
+	bpf_print_code(ip, match);
+}
+
+static void bpf_fcheck(struct xt_fcheck_call *cb)
+{
+	if (((!!(cb->xflags & (1 << O_BCODE_STDIN))) ^
+	     (!!(cb->xflags & (1 << O_BCODE_FILE)))) == 0)
+		xtables_error(PARAMETER_PROBLEM,
+			      "bpf: pass bytecode or bytecode-file, not both");
+}
+
+static void bpf_print(const void *ip, const struct xt_entry_match *match,
+		      int numeric)
+{
+	printf("match bpf ");
+	return bpf_print_code(ip, match);
+}
+
+static struct xtables_match bpf_match = {
+	.family		= NFPROTO_UNSPEC,
+	.name		= "bpf",
+	.version	= XTABLES_VERSION,
+	.size		= XT_ALIGN(sizeof(struct xt_bpf_info)),
+	.help		= bpf_help,
+	.print		= bpf_print,
+	.save		= bpf_save,
+	.x6_parse	= bpf_parse,
+	.x6_fcheck	= bpf_fcheck,
+	.x6_options	= bpf_opts,
+};
+
+void _init(void)
+{
+	xtables_register_match(&bpf_match);
+}
-- 
1.7.7.3