ip[6]tables: Add locking to prevent concurrent instances
There have been numerous complaints and bug reports over the years when admins
attempt to run more than one instance of iptables simultaneously. Currently
open bug reports which are related:
325: Parallel execution of the iptables is impossible
758: Retry iptables command on transient failure
764: Doing -Z twice in parallel breaks counters
822: iptables shows negative or other bad packet/byte counts
As Patrick notes in 325: "Since this has been a problem people keep running
into, I'd suggest to simply add some locking to iptables to catch the most
common case."
I started looking into alternatives to add locking, and of course the most
common/obvious solution is to use a pidfile. But this has various downsides,
such as if the application is terminated abnormally and the pidfile isn't
cleaned up. And this also requires a writable filesystem. Using a UNIX domain
socket file (e.g. in /var/run) has similar issues.
Starting in 2.2, Linux added support for abstract sockets. These sockets
require no filesystem, and automatically disappear once the application
terminates. This is the locking solution I chose to implement in ip[6]tables.
As an added bonus, since each network namespace has its own socket pool, an
ip[6]tables instance running in one namespace will not lock out an ip[6]tables
instance running in another namespace. A filesystem approach would have
to recognize and handle multiple network namespaces.
Signed-off-by: Phil Oester <kernel@linuxace.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/iptables/ip6tables.8.in b/iptables/ip6tables.8.in
index 05e0d0f..5b2a7d7 100644
--- a/iptables/ip6tables.8.in
+++ b/iptables/ip6tables.8.in
@@ -363,6 +363,13 @@
detailed information on the rule or rules to be printed. \fB\-v\fP may be
specified multiple times to possibly emit more detailed debug statements.
.TP
+\fB\-w\fP, \fB\-\-wait\fP
+Wait for the xtables lock.
+To prevent multiple instances of the program from running concurrently,
+an attempt will be made to obtain an exclusive lock at launch. By default,
+the program will exit if the lock cannot be obtained. This option will
+make the program wait until the exclusive lock can be obtained.
+.TP
\fB\-n\fP, \fB\-\-numeric\fP
Numeric output.
IP addresses and port numbers will be printed in numeric format.
diff --git a/iptables/ip6tables.c b/iptables/ip6tables.c
index c8d34e2..eededee 100644
--- a/iptables/ip6tables.c
+++ b/iptables/ip6tables.c
@@ -102,6 +102,7 @@
{.name = "numeric", .has_arg = 0, .val = 'n'},
{.name = "out-interface", .has_arg = 1, .val = 'o'},
{.name = "verbose", .has_arg = 0, .val = 'v'},
+ {.name = "wait", .has_arg = 0, .val = 'w'},
{.name = "exact", .has_arg = 0, .val = 'x'},
{.name = "version", .has_arg = 0, .val = 'V'},
{.name = "help", .has_arg = 2, .val = 'h'},
@@ -257,6 +258,7 @@
" network interface name ([+] for wildcard)\n"
" --table -t table table to manipulate (default: `filter')\n"
" --verbose -v verbose mode\n"
+" --wait -w wait for the xtables lock\n"
" --line-numbers print line numbers when listing\n"
" --exact -x expand numbers (display exact values)\n"
/*"[!] --fragment -f match second or further fragments only\n"*/
@@ -1293,6 +1295,7 @@
struct in6_addr *smasks = NULL, *dmasks = NULL;
int verbose = 0;
+ bool wait = false;
const char *chain = NULL;
const char *shostnetworkmask = NULL, *dhostnetworkmask = NULL;
const char *policy = NULL, *newname = NULL;
@@ -1328,7 +1331,7 @@
opts = xt_params->orig_opts;
while ((cs.c = getopt_long(argc, argv,
- "-: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:46",
+ "-:A:C:D:R:I:L::S::M:F::Z::N:X::E:P:Vh::o:p:s:d:j:i:bvwnt:m:xc:g:46",
opts, NULL)) != -1) {
switch (cs.c) {
/*
@@ -1573,6 +1576,10 @@
verbose++;
break;
+ case 'w':
+ wait = true;
+ break;
+
case 'm':
command_match(&cs);
break;
@@ -1724,6 +1731,14 @@
"chain name `%s' too long (must be under %u chars)",
chain, XT_EXTENSION_MAXNAMELEN);
+ /* Attempt to acquire the xtables lock */
+ if (!xtables_lock(wait)) {
+ fprintf(stderr, "Another app is currently holding the xtables lock. "
+ "Perhaps you want to use the -w option?\n");
+ xtables_free_opts(1);
+ exit(RESOURCE_PROBLEM);
+ }
+
/* only allocate handle if we weren't called with a handle */
if (!*handle)
*handle = ip6tc_init(*table);
diff --git a/iptables/iptables.8.in b/iptables/iptables.8.in
index 0fba603..6f31003 100644
--- a/iptables/iptables.8.in
+++ b/iptables/iptables.8.in
@@ -351,6 +351,13 @@
detailed information on the rule or rules to be printed. \fB\-v\fP may be
specified multiple times to possibly emit more detailed debug statements.
.TP
+\fB\-w\fP, \fB\-\-wait\fP
+Wait for the xtables lock.
+To prevent multiple instances of the program from running concurrently,
+an attempt will be made to obtain an exclusive lock at launch. By default,
+the program will exit if the lock cannot be obtained. This option will
+make the program wait until the exclusive lock can be obtained.
+.TP
\fB\-n\fP, \fB\-\-numeric\fP
Numeric output.
IP addresses and port numbers will be printed in numeric format.
diff --git a/iptables/iptables.c b/iptables/iptables.c
index 79fa37b..f857beb 100644
--- a/iptables/iptables.c
+++ b/iptables/iptables.c
@@ -99,6 +99,7 @@
{.name = "numeric", .has_arg = 0, .val = 'n'},
{.name = "out-interface", .has_arg = 1, .val = 'o'},
{.name = "verbose", .has_arg = 0, .val = 'v'},
+ {.name = "wait", .has_arg = 0, .val = 'w'},
{.name = "exact", .has_arg = 0, .val = 'x'},
{.name = "fragments", .has_arg = 0, .val = 'f'},
{.name = "version", .has_arg = 0, .val = 'V'},
@@ -251,6 +252,7 @@
" network interface name ([+] for wildcard)\n"
" --table -t table table to manipulate (default: `filter')\n"
" --verbose -v verbose mode\n"
+" --wait -w wait for the xtables lock\n"
" --line-numbers print line numbers when listing\n"
" --exact -x expand numbers (display exact values)\n"
"[!] --fragment -f match second or further fragments only\n"
@@ -1289,6 +1291,7 @@
struct in_addr *daddrs = NULL, *dmasks = NULL;
int verbose = 0;
+ bool wait = false;
const char *chain = NULL;
const char *shostnetworkmask = NULL, *dhostnetworkmask = NULL;
const char *policy = NULL, *newname = NULL;
@@ -1324,7 +1327,7 @@
opts = xt_params->orig_opts;
while ((cs.c = getopt_long(argc, argv,
- "-: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:46",
+ "-:A:C:D:R:I:L::S::M:F::Z::N:X::E:P:Vh::o:p:s:d:j:i:fbvwnt:m:xc:g:46",
opts, NULL)) != -1) {
switch (cs.c) {
/*
@@ -1567,6 +1570,10 @@
verbose++;
break;
+ case 'w':
+ wait = true;
+ break;
+
case 'm':
command_match(&cs);
break;
@@ -1721,6 +1728,14 @@
"chain name `%s' too long (must be under %u chars)",
chain, XT_EXTENSION_MAXNAMELEN);
+ /* Attempt to acquire the xtables lock */
+ if (!xtables_lock(wait)) {
+ fprintf(stderr, "Another app is currently holding the xtables lock. "
+ "Perhaps you want to use the -w option?\n");
+ xtables_free_opts(1);
+ exit(RESOURCE_PROBLEM);
+ }
+
/* only allocate handle if we weren't called with a handle */
if (!*handle)
*handle = iptc_init(*table);
diff --git a/iptables/xshared.c b/iptables/xshared.c
index e61c28c..6c9992e 100644
--- a/iptables/xshared.c
+++ b/iptables/xshared.c
@@ -6,9 +6,15 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
#include <xtables.h>
#include "xshared.h"
+#define XT_SOCKET_NAME "xtables"
+#define XT_SOCKET_LEN 8
+
/*
* Print out any special helps. A user might like to be able to add a --help
* to the commandline, and see expected results. So we call help for all
@@ -236,3 +242,30 @@
if (match->init != NULL)
match->init(match->m);
}
+
+bool xtables_lock(bool wait)
+{
+ int i = 0, ret, xt_socket;
+ struct sockaddr_un xt_addr;
+
+ memset(&xt_addr, 0, sizeof(xt_addr));
+ xt_addr.sun_family = AF_UNIX;
+ strcpy(xt_addr.sun_path+1, XT_SOCKET_NAME);
+ xt_socket = socket(AF_UNIX, SOCK_STREAM, 0);
+ /* If we can't even create a socket, fall back to prior (lockless) behavior */
+ if (xt_socket < 0)
+ return true;
+
+ while (1) {
+ ret = bind(xt_socket, (struct sockaddr*)&xt_addr,
+ offsetof(struct sockaddr_un, sun_path)+XT_SOCKET_LEN);
+ if (ret == 0)
+ return true;
+ else if (wait == false)
+ return false;
+ if (++i % 2 == 0)
+ fprintf(stderr, "Another app is currently holding the xtables lock; "
+ "waiting for it to exit...\n");
+ sleep(1);
+ }
+}
diff --git a/iptables/xshared.h b/iptables/xshared.h
index b804aaf..1e2b9b8 100644
--- a/iptables/xshared.h
+++ b/iptables/xshared.h
@@ -2,6 +2,7 @@
#define IPTABLES_XSHARED_H 1
#include <limits.h>
+#include <stdbool.h>
#include <stdint.h>
#include <netinet/in.h>
#include <net/if.h>
@@ -83,6 +84,7 @@
extern int subcmd_main(int, char **, const struct subcommand *);
extern void xs_init_target(struct xtables_target *);
extern void xs_init_match(struct xtables_match *);
+extern bool xtables_lock(bool wait);
extern const struct xtables_afinfo *afinfo;
