From 8c404ef02f0122ec90b48e122777ff6bfa715d7f Mon Sep 17 00:00:00 2001 From: Alexander Couzens Date: Fri, 17 May 2019 11:14:46 +0200 Subject: [PATCH] iptables.c: lock the xtables.lock When using fw3 together with other applications or scripts a race conditions might occur. When fw3 is preparing the new tables, another application can use the executable `iptables` which modifies the kernel-tables. libxtables will notify this and fails when fw3 is committing the changes resulting in a failed firewall. Now waits in a while loop until the lock is gone, activate the lock itself and applies changes. To reproduce the bug the following two scripts should run in parrallel, after a few seconds the latter stop and leaves a broken firewall: while true; do iptables -N locking; done and while [ "$(iptables -w -L OUTPUT | wc -l)" -gt 2 ]; do fw3 reload; done The following message will appear Warning: iptc_commit(): Resource temporarily unavailable and connectivity is gone. Tested in an LXC and Qemu container. Signed-off-by: Alexander Couzens [fixed waiting for unlock and commit message] Signed-off-by: Paul Spooren --- iptables.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/iptables.c b/iptables.c index a095621..559fe7d 100644 --- a/iptables.c +++ b/iptables.c @@ -55,6 +55,8 @@ #include "iptables.h" +#define XT_LOCK_NAME "/var/run/xtables.lock" +static int xt_lock_fd = -1; struct fw3_ipt_rule { struct fw3_ipt_handle *h; @@ -168,6 +170,11 @@ fw3_ipt_open(enum fw3_family family, enum fw3_table table) xtables_init(); + while (!fw3_lock_path(&xt_lock_fd, XT_LOCK_NAME)) { + warn("Currently busy xtables.lock - wait 1 second"); + sleep(1); + } + if (family == FW3_FAMILY_V6) { #ifndef DISABLE_IPV6 @@ -192,6 +199,7 @@ fw3_ipt_open(enum fw3_family family, enum fw3_table table) if (!h->handle) { free(h); + fw3_unlock_path(&xt_lock_fd, XT_LOCK_NAME); return NULL; } @@ -561,6 +569,7 @@ fw3_ipt_commit(struct fw3_ipt_handle *h) void fw3_ipt_close(struct fw3_ipt_handle *h) { + fw3_unlock_path(&xt_lock_fd, XT_LOCK_NAME); free(h); } -- 2.30.2