Changes:
- v3
- more informative error messages and man page
- v2
- update to match latest kernel module (fixed size match struct)
- add manual page
- fix save/restore
- fix matching whole program on delete
Support filtering using Linux Socket Filters
---
extensions/libxt_bpf.c | 193 +++++++++++++++++++++++++++++++++++++++++++++++
extensions/libxt_bpf.man | 35 +++++++++
2 files changed, 228 insertions(+)
create mode 100644 extensions/libxt_bpf.c
create mode 100644 extensions/libxt_bpf.man
diff --git a/extensions/libxt_bpf.c b/extensions/libxt_bpf.c
new file mode 100644
index 0000000..15dc870
--- /dev/null
+++ b/extensions/libxt_bpf.c
@@ -0,0 +1,193 @@
+/*
+ * Xtables BPF extension
+ *
+ * Written by Willem de Bruijn (willemb@xxxxxxxxxx)
+ * Copyright Google, Inc. 2013
+ * 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,
+};
+
+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");
+ if (bi->bpf_program_num_elem > XT_BPF_MAX_NUM_INSTR)
+ xtables_error(PARAMETER_PROBLEM,
+ "bpf: number of instructions exceeds maximum");
+
+ /* 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: real program length exceeds"
+ " the encoded length parameter");
+ 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);
+ i++;
+ }
+
+ if (i != bi->bpf_program_num_elem)
+ xtables_error(PARAMETER_PROBLEM,
+ "bpf: parsed program length is less than the"
+ " encoded length parameter");
+}
+
+static void bpf_parse_file(struct xt_option_call *cb, const char *filepath)
+{
+ struct stat stats;
+ char *contents;
+ int fd, len = 0, ret;
+
+ fd = open(filepath, O_RDONLY);
+ if (fd == -1)
+ xtables_error(PARAMETER_PROBLEM, "bpf: error opening file: %s",
+ strerror(errno));
+ 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(" --bytecode \"%hu,", info->bpf_program_num_elem);
+ bpf_print_code(ip, match);
+ printf("\"");
+}
+
+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)),
+ .userspacesize = XT_ALIGN(offsetof(struct xt_bpf_info, filter)),
+ .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);
+}
diff --git a/extensions/libxt_bpf.man b/extensions/libxt_bpf.man
new file mode 100644
index 0000000..468c023
--- /dev/null
+++ b/extensions/libxt_bpf.man
@@ -0,0 +1,35 @@
+.TP
+Match using Linux Socket Filter. Expects a BPF program in decimal format for a device without link layer. This is the format generated by \fBtcpdump \-ddd \-i $DEV\fP, if $DEV is of type DLT_RAW.
+.TP
+\fB\-\-bytecode\-file\fP \fIfilename\fP
+Pass the program stored in a file.
+For example:
+.IP
+iptables \-A OUTPUT \-m bpf \-\-bytecode-file program.bpf \-j ACCEPT
+.IP
+The file format matches the output of the tcpdump command: one line
+that stores the number of instructions, followed by one line for each
+instruction. Instruction lines follow the pattern 'u16 u8 u8 u32'
+in decimal notation. Fields encode the operation, jump offset if true,
+jump offset if false and generic multiuse field 'K'. Comments are not
+supported.
+.IP
+For example, to read only packets matching 'ip proto 6', insert the
+following, without the comments or trailing whitespace:
+.br
+4 # number of instructions
+.br
+48 0 0 9 # load byte ip->proto
+.br
+21 0 1 6 # jump equal IPPROTO_TCP
+.br
+6 0 0 1 # return pass (non-zero)
+.br
+6 0 0 0 # return fail (zero)
+.TP
+\fB\-\-bytecode\fP \fIcode\fP
+Pass the program on the command line. In this case all end-lines
+must have been converted to commas (for instance using `tr '\\n' ','`).
+For example, the same program passed on the command line becomes:
+.IP
+iptables \-A OUTPUT \-m bpf \-\-bytecode '4,48 0 0 9,21 0 1 6,6 0 0 1,6 0 0 0,' \-j ACCEPT
--
1.8.1
--
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