iptables: add -C to check for existing rules

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@wertarbyte.de>
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>

diff --git a/include/libiptc/libip6tc.h b/include/libiptc/libip6tc.h
index 33ec69d2d5909af41f2fedb6c4588789e7919611..9796574ffefed4645c9ae9045fe089cdaddb6545 100644 (file)
--- a/include/libiptc/libip6tc.h
+++ b/include/libiptc/libip6tc.h
@@ -80,6 +80,12 @@ int ip6tc_append_entry(const ip6t_chainlabel chain,
                       const struct ip6t_entry *e,
                       struct ip6tc_handle *handle);
 
+/* Check whether a matching rule exists */
+int ip6tc_check_entry(const ip6t_chainlabel chain,
+                      const struct ip6t_entry *origfw,
+                      unsigned char *matchmask,
+                      struct ip6tc_handle *handle);
+
 /* Delete the first rule in `chain' which matches `fw'. */
 int ip6tc_delete_entry(const ip6t_chainlabel chain,
                       const struct ip6t_entry *origfw,

diff --git a/include/libiptc/libiptc.h b/include/libiptc/libiptc.h
index 5d782dab98562201f66b99e4b2bffe92d1985504..4355ac9216bb2b36cfc695cda8ffd0eab7861b6c 100644 (file)
--- 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 mathching rule 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/ip6tables.8.in b/ip6tables.8.in
index 4306934397a65c381efc9f0d83689716e195be0a..7690ba14d2ec4744dc6f66157b816db620895460 100644 (file)
--- a/ip6tables.8.in
+++ b/ip6tables.8.in
@@ -27,8 +27,8 @@
 .SH NAME
 ip6tables \(em IPv6 packet filter administration
 .SH SYNOPSIS
-\fBip6tables\fP [\fB\-t\fP \fItable\fP] {\fB\-A\fP|\fB\-D\fP} \fIchain
-rule-specification\fP [\fIoptions...\fP]
+\fBip6tables\fP [\fB\-t\fP \fItable\fP] {\fB\-A\fP|\fB\-C\fP|\fB\-D\fP}
+\fIchain rule-specification\fP [\fIoptions...\fP]
 .PP
 \fBip6tables\fP [\fB\-t\fP \fItable\fP] \fB\-I\fP \fIchain\fP [\fIrulenum\fP]
 \fIrule-specification\fP [\fIoptions...\fP]
@@ -139,6 +139,12 @@ Append one or more rules to the end of the selected chain.
 When the source and/or destination names resolve to more than one
 address, a rule will be added for each possible address combination.
 .TP
+\fB\-C\fP, \fB\-\-check\fP \fIchain rule-specification\fP
+Check whether a rule matching the specification does exist in the
+selected chain. This command uses the same logic as \fB\-D\fP to
+find a matching entry, but does not alter the existing iptables
+configuration and uses its exit code to indicate success or failure.
+.TP
 \fB\-D\fP, \fB\-\-delete\fP \fIchain rule-specification\fP
 .ns
 .TP

diff --git a/ip6tables.c b/ip6tables.c
index 06f570b19202f1265899e93f64045acfb4ba46b4..96a0fdcf979da5306c55fe84f085dc25aa9d003f 100644 (file)
--- a/ip6tables.c
+++ b/ip6tables.c
@@ -82,9 +82,10 @@
 #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 NUMBER_OF_OPT  ARRAY_SIZE(optflags)
 static const char optflags[]
@@ -93,6 +94,7 @@ 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'},
 /*SET_POLICY*/{'x','x','x','x','x',' ','x','x','x','x',' '},
 /*RENAME*/    {'x','x','x','x','x',' ','x','x','x','x','x'},
-/*LIST_RULES*/{'x','x','x','x','x',' ','x','x','x','x','x'}
+/*LIST_RULES*/{'x','x','x','x','x',' ','x','x','x','x','x'},
+/*CHECK*/     {'x',' ',' ',' ',' ',' ','x',' ',' ','x','x'},
 };
 
 static const unsigned int inverse_for_options[NUMBER_OF_OPT] =
@@ -208,7 +211,7 @@ 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"
@@ -226,6 +229,7 @@ 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"
@@ -824,6 +828,36 @@ delete_entry(const ip6t_chainlabel chain,
        return ret;
 }
 
+static int
+check_entry(const ip6t_chainlabel chain, struct ip6t_entry *fw,
+           unsigned int nsaddrs, const struct in6_addr *saddrs,
+           const struct in6_addr *smasks, unsigned int ndaddrs,
+           const struct in6_addr *daddrs, const struct in6_addr *dmasks,
+           bool verbose, struct ip6tc_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->ipv6.src = saddrs[i];
+               fw->ipv6.smsk = smasks[i];
+               for (j = 0; j < ndaddrs; j++) {
+                       fw->ipv6.dst = daddrs[j];
+                       fw->ipv6.dmsk = dmasks[j];
+                       if (verbose)
+                               print_firewall_line(fw, handle);
+                       ret &= ip6tc_check_entry(chain, fw, mask, handle);
+               }
+       }
+
+       free(mask);
+       return ret;
+}
+
 int
 for_each_chain(int (*fn)(const ip6t_chainlabel, int, struct ip6tc_handle *),
               int verbose, int builtinstoo, struct ip6tc_handle *handle)
@@ -1393,7 +1427,7 @@ int do_command6(int argc, char *argv[], char **table, struct ip6tc_handle **hand
 
        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:bvnt:m:xc:g:",
+          "-:A:C:D:R:I:L::S::M:F::Z::N:X::E:P:Vh::o:p:s:d:j:i:bvnt:m:xc:g:",
                                           opts, NULL)) != -1) {
                switch (cs.c) {
                        /*
@@ -1405,6 +1439,12 @@ int do_command6(int argc, char *argv[], char **table, struct ip6tc_handle **hand
                        chain = optarg;
                        break;
 
+               case 'C':
+                       add_command(&command, CMD_CHECK, CMD_NONE,
+                                   cs.invert);
+                       chain = optarg;
+                       break;
+
                case 'D':
                        add_command(&command, CMD_DELETE, CMD_NONE,
                                    cs.invert);
@@ -1742,7 +1782,7 @@ int do_command6(int argc, char *argv[], char **table, struct ip6tc_handle **hand
                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";
                if (!(cs.options & OPT_SOURCE))
@@ -1788,6 +1828,7 @@ int do_command6(int argc, char *argv[], char **table, struct ip6tc_handle **hand
 
        if (command == CMD_APPEND
            || command == CMD_DELETE
+           || command == CMD_CHECK
            || command == CMD_INSERT
            || command == CMD_REPLACE) {
                if (strcmp(chain, "PREROUTING") == 0
@@ -1876,6 +1917,13 @@ int do_command6(int argc, char *argv[], char **table, struct ip6tc_handle **hand
        case CMD_DELETE_NUM:
                ret = ip6tc_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/iptables.8.in b/iptables.8.in
index f36d220ecf659b80c16ea0c6881c20e1bf8c87ba..4b97bc3dba432581661a3dbed91db8ae96ed2e1f 100644 (file)
--- a/iptables.8.in
+++ b/iptables.8.in
@@ -25,7 +25,8 @@
 .SH NAME
 iptables \(em administration tool for IPv4 packet filtering and NAT
 .SH SYNOPSIS
-\fBiptables\fP [\fB\-t\fP \fItable\fP] {\fB\-A\fP|\fB\-D\fP} \fIchain\fP \fIrule-specification\fP
+\fBiptables\fP [\fB\-t\fP \fItable\fP] {\fB\-A\fP|\fB\-C\fP|\fB\-D\fP}
+\fIchain\fP \fIrule-specification\fP
 .PP
 \fBiptables\fP [\fB\-t\fP \fItable\fP] \fB\-I\fP \fIchain\fP [\fIrulenum\fP] \fIrule-specification\fP
 .PP
@@ -144,6 +145,12 @@ Append one or more rules to the end of the selected chain.
 When the source and/or destination names resolve to more than one
 address, a rule will be added for each possible address combination.
 .TP
+\fB\-C\fP, \fB\-\-check\fP \fIchain rule-specification\fP
+Check whether a rule matching the specification does exist in the
+selected chain. This command uses the same logic as \fB\-D\fP to
+find a matching entry, but does not alter the existing iptables
+configuration and uses its exit code to indicate success or failure.
+.TP
 \fB\-D\fP, \fB\-\-delete\fP \fIchain rule-specification\fP
 .ns
 .TP

diff --git a/iptables.c b/iptables.c
index a73df3ea93c91cbac3124c3da0365c1ebd0cef62..cff4a7b3d41d09eb1584dde61c34fe341c215f76 100644 (file)
--- 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 +831,36 @@ 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,
+           bool 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 +1457,7 @@ 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:C:D: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) {
                        /*
@@ -1435,6 +1469,12 @@ int do_command(int argc, char *argv[], char **table, struct iptc_handle **handle
                        chain = optarg;
                        break;
 
+               case 'C':
+                       add_command(&command, CMD_CHECK, CMD_NONE,
+                                   cs.invert);
+                       chain = optarg;
+                       break;
+
                case 'D':
                        add_command(&command, CMD_DELETE, CMD_NONE,
                                    cs.invert);
@@ -1778,7 +1818,7 @@ 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 +1864,7 @@ 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 +1955,13 @@ 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 c1d78e2bb9d271e73d87e2d0d342254ca9ddb945..e2d2a5ee0eba3c39de86e0f4eb955ecc829bb09f 100644 (file)
--- 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/libip6tc.c b/libiptc/libip6tc.c
index 27fe4c4e3ddf33296d241dcb9f16abf7518c93f3..c1508cd598b75cf7fb5100c218a3b4ea67ba653a 100644 (file)
--- a/libiptc/libip6tc.c
+++ b/libiptc/libip6tc.c
@@ -71,6 +71,7 @@ typedef unsigned int socklen_t;
 #define TC_INSERT_ENTRY                ip6tc_insert_entry
 #define TC_REPLACE_ENTRY       ip6tc_replace_entry
 #define TC_APPEND_ENTRY                ip6tc_append_entry
+#define TC_CHECK_ENTRY         ip6tc_check_entry
 #define TC_DELETE_ENTRY                ip6tc_delete_entry
 #define TC_DELETE_NUM_ENTRY    ip6tc_delete_num_entry
 #define TC_FLUSH_ENTRIES       ip6tc_flush_entries

diff --git a/libiptc/libiptc.c b/libiptc/libiptc.c
index 7a9c74281a9795497941f8521b1fb52d0cb28608..d3b1c5173f6f3faceb47f45173e5b6e9b1f5ab16 100644 (file)
--- a/libiptc/libiptc.c
+++ b/libiptc/libiptc.c
@@ -31,6 +31,7 @@
  */
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <stdbool.h>
 #include <xtables.h>
 
 #include "linux_list.h"
@@ -1956,12 +1957,11 @@ 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,
-               const STRUCT_ENTRY *origfw,
-               unsigned char *matchmask,
-               struct xtc_handle *handle)
+
+/* 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,
+                       bool dry_run)
 {
        struct chain_head *c;
        struct rule_head *r, *i;
@@ -2005,6 +2005,10 @@ 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
                 * pointer will then point to real next node */
@@ -2027,6 +2031,20 @@ 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, true);
+}
+
+/* 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, false);
+}
 
 /* Delete the rule in position `rulenum' in `chain'. */
 int