path: root/iptables/iptables.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/iptables.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/iptables.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/iptables/iptables.c b/iptables/iptables.c
index 04be5abb..62731c5e 100644
--- a/iptables/iptables.c
+++ b/iptables/iptables.c
@@ -1766,7 +1766,7 @@ int do_command4(int argc, char *argv[], char **table,
generic_opt_check(command, cs.options);
/* Attempt to acquire the xtables lock */
- if (!restore && !xtables_lock(wait, &wait_interval)) {
+ if (!restore && xtables_lock(wait, &wait_interval) == XT_LOCK_BUSY) {
fprintf(stderr, "Another app is currently holding the xtables lock. ");
if (wait == 0)
fprintf(stderr, "Perhaps you want to use the -w option?\n");