Hi Lorenzo, On Thu, Mar 16, 2017 at 04:55:02PM +0900, Lorenzo Colitti wrote: > 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". My concern with this is that one iptables-restore instance may postpone any other iptables call indefinitely, by simply typing "*filter" with no COMMIT ever. The other instance can simply kill this process, as they would be both running with CAP_NET_ADMIN though. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
