path: root/iptables/xshared.c
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.c
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.c')
1 files changed, 12 insertions, 6 deletions
diff --git a/iptables/xshared.c b/iptables/xshared.c
index 06147d18..3fbe3b1a 100644
--- a/iptables/xshared.c
+++ b/iptables/xshared.c
@@ -246,7 +246,7 @@ void xs_init_match(struct xtables_match *match)
-bool xtables_lock(int wait, struct timeval *wait_interval)
+int xtables_lock(int wait, struct timeval *wait_interval)
struct timeval time_left, wait_time;
int fd, i = 0;
@@ -256,22 +256,22 @@ bool xtables_lock(int wait, struct timeval *wait_interval)
fd = open(XT_LOCK_NAME, O_CREAT, 0600);
if (fd < 0)
- return true;
if (wait == -1) {
if (flock(fd, LOCK_EX) == 0)
- return true;
+ return fd;
fprintf(stderr, "Can't lock %s: %s\n", XT_LOCK_NAME,
- return false;
+ return XT_LOCK_BUSY;
while (1) {
if (flock(fd, LOCK_EX | LOCK_NB) == 0)
- return true;
+ return fd;
else if (timercmp(&time_left, wait_interval, <))
- return false;
+ return XT_LOCK_BUSY;
if (++i % 10 == 0) {
fprintf(stderr, "Another app is currently holding the xtables lock; "
@@ -285,6 +285,12 @@ bool xtables_lock(int wait, struct timeval *wait_interval)
+void xtables_unlock(int lock)
+ if (lock >= 0)
+ close(lock);
int parse_wait_time(int argc, char *argv[])
int wait = -1;