It is often useful to check whether a specific rule is already present
in a chain without actually modifying the iptables config.
Services like fail2ban usually employ techniques like grepping through
the output of "iptables -L" which is quite error prone.
This patch adds a new operation -C to the iptables command which mostly
works like -D; it can detect and indicate the existence of the specified
rule by modifying the exit code. The new operation TC_CHECK_ENTRY uses
the same code as the -D operation, whose functions got a dry-run
parameter appended.
Signed-off-by: Stefan Tomanek <stefan.tomanek@xxxxxxxxxxxxx>
---
include/libiptc/libiptc.h | 6 ++++
iptables.c | 66 ++++++++++++++++++++++++++++++++++++++++----
libiptc/libip4tc.c | 1 +
libiptc/libiptc.c | 34 ++++++++++++++++++++---
4 files changed, 97 insertions(+), 10 deletions(-)
diff --git a/include/libiptc/libiptc.h b/include/libiptc/libiptc.h
index 5d782da..21b20df 100644
--- a/include/libiptc/libiptc.h
+++ b/include/libiptc/libiptc.h
@@ -88,6 +88,12 @@ int iptc_append_entry(const ipt_chainlabel chain,
const struct ipt_entry *e,
struct iptc_handle *handle);
+/* Check whether a rule mathching `e' exists */
+int iptc_check_entry(const ipt_chainlabel chain,
+ const struct ipt_entry *origfw,
+ unsigned char *matchmask,
+ struct iptc_handle *handle);
+
/* Delete the first rule in `chain' which matches `e', subject to
matchmask (array of length == origfw) */
int iptc_delete_entry(const ipt_chainlabel chain,
diff --git a/iptables.c b/iptables.c
index a73df3e..f5d2cd5 100644
--- a/iptables.c
+++ b/iptables.c
@@ -79,9 +79,10 @@
#define CMD_RENAME_CHAIN 0x0800U
#define CMD_LIST_RULES 0x1000U
#define CMD_ZERO_NUM 0x2000U
-#define NUMBER_OF_CMD 15
+#define CMD_CHECK 0x4000U
+#define NUMBER_OF_CMD 16
static const char cmdflags[] = { 'I', 'D', 'D', 'R', 'A', 'L', 'F', 'Z',
- 'Z', 'N', 'X', 'P', 'E', 'S' };
+ 'Z', 'N', 'X', 'P', 'E', 'S', 'C' };
#define OPT_FRAGMENT 0x00800U
#define NUMBER_OF_OPT ARRAY_SIZE(optflags)
@@ -91,6 +92,7 @@ static const char optflags[]
static struct option original_opts[] = {
{.name = "append", .has_arg = 1, .val = 'A'},
{.name = "delete", .has_arg = 1, .val = 'D'},
+ {.name = "check", .has_arg = 1, .val = 'C'},
{.name = "insert", .has_arg = 1, .val = 'I'},
{.name = "replace", .has_arg = 1, .val = 'R'},
{.name = "list", .has_arg = 2, .val = 'L'},
@@ -165,7 +167,8 @@ static const char commands_v_options[NUMBER_OF_CMD][NUMBER_OF_OPT] =
/*DEL_CHAIN*/ {'x','x','x','x','x',' ','x','x','x','x','x','x'},
/*SET_POLICY*/{'x','x','x','x','x',' ','x','x','x','x',' ','x'},
/*RENAME*/ {'x','x','x','x','x',' ','x','x','x','x','x','x'},
-/*LIST_RULES*/{'x','x','x','x','x',' ','x','x','x','x','x','x'}
+/*LIST_RULES*/{'x','x','x','x','x',' ','x','x','x','x','x','x'},
+/*CHECK*/ {'x',' ',' ',' ',' ',' ','x',' ',' ','x','x',' '}
};
static const int inverse_for_options[NUMBER_OF_OPT] =
@@ -221,7 +224,7 @@ static void
exit_printhelp(const struct xtables_rule_match *matches)
{
printf("%s v%s\n\n"
-"Usage: %s -[AD] chain rule-specification [options]\n"
+"Usage: %s -[ACD] chain rule-specification [options]\n"
" %s -I chain [rulenum] rule-specification [options]\n"
" %s -R chain rulenum rule-specification [options]\n"
" %s -D chain rulenum [options]\n"
@@ -239,6 +242,7 @@ exit_printhelp(const struct xtables_rule_match *matches)
"Commands:\n"
"Either long or short options are allowed.\n"
" --append -A chain Append to chain\n"
+" --check -C chain Check for the existence of a rule\n"
" --delete -D chain Delete matching rule from chain\n"
" --delete -D chain rulenum\n"
" Delete rule rulenum (1 = first) from chain\n"
@@ -827,6 +831,42 @@ delete_entry(const ipt_chainlabel chain,
return ret;
}
+static int
+check_entry(const ipt_chainlabel chain,
+ struct ipt_entry *fw,
+ unsigned int nsaddrs,
+ const struct in_addr saddrs[],
+ const struct in_addr smasks[],
+ unsigned int ndaddrs,
+ const struct in_addr daddrs[],
+ const struct in_addr dmasks[],
+ int verbose,
+ struct iptc_handle *handle,
+ struct xtables_rule_match *matches,
+ const struct xtables_target *target)
+{
+ unsigned int i, j;
+ int ret = 1;
+ unsigned char *mask;
+
+ mask = make_delete_mask(matches, target);
+ for (i = 0; i < nsaddrs; i++) {
+ fw->ip.src.s_addr = saddrs[i].s_addr;
+ fw->ip.smsk.s_addr = smasks[i].s_addr;
+ for (j = 0; j < ndaddrs; j++) {
+ fw->ip.dst.s_addr = daddrs[j].s_addr;
+ fw->ip.dmsk.s_addr = dmasks[j].s_addr;
+ if (verbose)
+ print_firewall_line(fw, handle);
+ ret &= iptc_check_entry(chain, fw, mask, handle);
+ }
+ }
+ free(mask);
+
+ return ret;
+}
+
+
int
for_each_chain(int (*fn)(const ipt_chainlabel, int, struct iptc_handle *),
int verbose, int builtinstoo, struct iptc_handle *handle)
@@ -1423,7 +1463,7 @@ int do_command(int argc, char *argv[], char **table, struct iptc_handle **handle
opts = xt_params->orig_opts;
while ((cs.c = getopt_long(argc, argv,
- "-:A:D:R:I:L::S::M:F::Z::N:X::E:P:Vh::o:p:s:d:j:i:fbvnt:m:xc:g:",
+ "-:A:D:C:R:I:L::S::M:F::Z::N:X::E:P:Vh::o:p:s:d:j:i:fbvnt:m:xc:g:",
opts, NULL)) != -1) {
switch (cs.c) {
/*
@@ -1446,6 +1486,12 @@ int do_command(int argc, char *argv[], char **table, struct iptc_handle **handle
}
break;
+ case 'C':
+ add_command(&command, CMD_CHECK, CMD_NONE,
+ cs.invert);
+ chain = optarg;
+ break;
+
case 'R':
add_command(&command, CMD_REPLACE, CMD_NONE,
cs.invert);
@@ -1778,7 +1824,7 @@ int do_command(int argc, char *argv[], char **table, struct iptc_handle **handle
xtables_error(PARAMETER_PROBLEM,
"nothing appropriate following !");
- if (command & (CMD_REPLACE | CMD_INSERT | CMD_DELETE | CMD_APPEND)) {
+ if (command & (CMD_REPLACE | CMD_INSERT | CMD_DELETE | CMD_APPEND | CMD_CHECK)) {
if (!(cs.options & OPT_DESTINATION))
dhostnetworkmask = "0.0.0.0/0";
if (!(cs.options & OPT_SOURCE))
@@ -1824,6 +1870,7 @@ int do_command(int argc, char *argv[], char **table, struct iptc_handle **handle
if (command == CMD_APPEND
|| command == CMD_DELETE
+ || command == CMD_CHECK
|| command == CMD_INSERT
|| command == CMD_REPLACE) {
if (strcmp(chain, "PREROUTING") == 0
@@ -1914,6 +1961,13 @@ int do_command(int argc, char *argv[], char **table, struct iptc_handle **handle
case CMD_DELETE_NUM:
ret = iptc_delete_num_entry(chain, rulenum - 1, *handle);
break;
+ case CMD_CHECK:
+ ret = check_entry(chain, e,
+ nsaddrs, saddrs, smasks,
+ ndaddrs, daddrs, dmasks,
+ cs.options&OPT_VERBOSE,
+ *handle, cs.matches, cs.target);
+ break;
case CMD_REPLACE:
ret = replace_entry(chain, e, rulenum - 1,
saddrs, smasks, daddrs, dmasks,
diff --git a/libiptc/libip4tc.c b/libiptc/libip4tc.c
index c1d78e2..e2d2a5e 100644
--- a/libiptc/libip4tc.c
+++ b/libiptc/libip4tc.c
@@ -76,6 +76,7 @@ typedef unsigned int socklen_t;
#define TC_INSERT_ENTRY iptc_insert_entry
#define TC_REPLACE_ENTRY iptc_replace_entry
#define TC_APPEND_ENTRY iptc_append_entry
+#define TC_CHECK_ENTRY iptc_check_entry
#define TC_DELETE_ENTRY iptc_delete_entry
#define TC_DELETE_NUM_ENTRY iptc_delete_num_entry
#define TC_FLUSH_ENTRIES iptc_flush_entries
diff --git a/libiptc/libiptc.c b/libiptc/libiptc.c
index 7a9c742..2803fa0 100644
--- a/libiptc/libiptc.c
+++ b/libiptc/libiptc.c
@@ -1956,12 +1956,14 @@ is_same(const STRUCT_ENTRY *a,
const STRUCT_ENTRY *b,
unsigned char *matchmask);
-/* Delete the first rule in `chain' which matches `fw'. */
-int
-TC_DELETE_ENTRY(const IPT_CHAINLABEL chain,
+
+/* find the first rule in `chain' which matches `fw' and remove it unless dry_run is set */
+static int
+delete_entry(const IPT_CHAINLABEL chain,
const STRUCT_ENTRY *origfw,
unsigned char *matchmask,
- struct xtc_handle *handle)
+ struct xtc_handle *handle,
+ int dry_run)
{
struct chain_head *c;
struct rule_head *r, *i;
@@ -2004,6 +2006,10 @@ TC_DELETE_ENTRY(const IPT_CHAINLABEL chain,
if (!target_same(r, i, mask))
continue;
+
+ /* if we are just doing a dry run, we simply skip the rest */
+ if (dry_run)
+ return 1;
/* If we are about to delete the rule that is the
* current iterator, move rule iterator back. next
@@ -2027,6 +2033,26 @@ TC_DELETE_ENTRY(const IPT_CHAINLABEL chain,
return 0;
}
+/* check whether a specified rule is present */
+int
+TC_CHECK_ENTRY(const IPT_CHAINLABEL chain,
+ const STRUCT_ENTRY *origfw,
+ unsigned char *matchmask,
+ struct xtc_handle *handle)
+{
+ /* do a dry-run delete to find out whether a matching rule exists */
+ return delete_entry(chain, origfw, matchmask, handle, 1);
+}
+
+/* Delete the first rule in `chain' which matches `fw'. */
+int
+TC_DELETE_ENTRY(const IPT_CHAINLABEL chain,
+ const STRUCT_ENTRY *origfw,
+ unsigned char *matchmask,
+ struct xtc_handle *handle)
+{
+ return delete_entry(chain, origfw, matchmask, handle, 0);
+}
/* Delete the rule in position `rulenum' in `chain'. */
int
--
1.7.2.3
--
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