path: root/iptables/xshared.h
diff options
authorLorenzo Colitti <>2017-03-16 16:55:02 +0900
committerPablo Neira Ayuso <>2017-03-21 14:54:03 +0100
commit999eaa241212d3952ddff39a99d0d55a74e3639e (patch)
treed68411f36cc17dd8fe2672f1ece0184a4e58f9e6 /iptables/xshared.h
parent6e2e169eb66b63d2991e1c7ada931e3cdb0ced32 (diff)
iptables-restore: support acquiring the lock.
Currently, ip[6]tables-restore does not perform any locking, so it is not safe to use concurrently with ip[6]tables. This patch makes ip[6]tables-restore wait for the lock if -w was specified. Arguments to -w and -W are supported in the same was as they are in ip[6]tables. The lock is not acquired on startup. Instead, it is acquired when a new table handle is created (on encountering '*') and released when the table is committed (COMMIT). This makes it possible to keep long-running iptables-restore processes in the background (for example, reading commands from a pipe opened by a system management daemon) and simultaneously run iptables commands. If -w is not specified, then the command proceeds without taking the lock. Tested as follows: 1. Run iptables-restore -w, and check that iptables commands work with or without -w. 2. Type "*filter" into the iptables-restore input. Verify that a) ip[6]tables commands without -w fail with "another app is currently holding the xtables lock...". b) ip[6]tables commands with "-w 2" fail after 2 seconds. c) ip[6]tables commands with "-w" hang until "COMMIT" is typed into the iptables-restore window. 3. With the lock held by an ip6tables-restore process: strace -e flock /tmp/iptables/sbin/iptables-restore -w 1 -W 100000 shows 11 calls to flock and fails. 4. Run an iptables-restore with -w and one without -w, and check: a) Type "*filter" in the first and then the second, and the second exits with an error. b) Type "*filter" in the second and "*filter" "-S" "COMMIT" into the first. The rules are listed only when the first copy sees "COMMIT". Signed-off-by: Narayan Kamath <> Signed-off-by: Lorenzo Colitti <> Signed-off-by: Pablo Neira Ayuso <>
Diffstat (limited to 'iptables/xshared.h')
1 files changed, 22 insertions, 1 deletions
diff --git a/iptables/xshared.h b/iptables/xshared.h
index d8a697ae..539e6c24 100644
--- a/iptables/xshared.h
+++ b/iptables/xshared.h
@@ -86,7 +86,28 @@ extern struct xtables_match *load_proto(struct iptables_command_state *);
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 *);
-bool xtables_lock(int wait, struct timeval *wait_interval);
+ * Values for the iptables lock.
+ *
+ * A value >= 0 indicates the lock filedescriptor. Other values are:
+ *
+ * XT_LOCK_UNSUPPORTED : The system does not support locking, execution will
+ * proceed lockless.
+ *
+ * XT_LOCK_BUSY : The lock was held by another process. xtables_lock only
+ * returns this value when |wait| == false. If |wait| == true, xtables_lock
+ * will not return unless the lock has been acquired.
+ *
+ * XT_LOCK_NOT_ACQUIRED : We have not yet attempted to acquire the lock.
+ */
+enum {
+ XT_LOCK_BUSY = -1,
+extern int xtables_lock(int wait, struct timeval *tv);
+extern void xtables_unlock(int lock);
int parse_wait_time(int argc, char *argv[]);
void parse_wait_interval(int argc, char *argv[], struct timeval *wait_interval);