From f95d7a46bc5722767c30ee223c8b67dd0f2e8793 Mon Sep 17 00:00:00 2001 From: Kevin Cernekee Date: Thu, 26 Jan 2017 14:49:44 -0800 Subject: [PATCH] netfilter: ctnetlink: Fix regression in CTA_HELP processing Prior to Linux 4.4, it was usually harmless to send a CTA_HELP attribute containing the name of the current helper. That is no longer the case: as of Linux 4.4, if ctnetlink_change_helper() returns an error from the ct->master check, processing of the request will fail, skipping the NFQA_EXP attribute (if present). This patch changes the behavior to improve compatibility with user programs that expect the kernel interface to work the way it did prior to Linux 4.4. If a user program specifies CTA_HELP but the argument matches the current conntrack helper name, ignore it instead of generating an error. Signed-off-by: Kevin Cernekee Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_netlink.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c index bf04b7e9d6f7..6806b5e73567 100644 --- a/net/netfilter/nf_conntrack_netlink.c +++ b/net/netfilter/nf_conntrack_netlink.c @@ -1478,14 +1478,23 @@ static int ctnetlink_change_helper(struct nf_conn *ct, struct nlattr *helpinfo = NULL; int err; - /* don't change helper of sibling connections */ - if (ct->master) - return -EBUSY; - err = ctnetlink_parse_help(cda[CTA_HELP], &helpname, &helpinfo); if (err < 0) return err; + /* don't change helper of sibling connections */ + if (ct->master) { + /* If we try to change the helper to the same thing twice, + * treat the second attempt as a no-op instead of returning + * an error. + */ + if (help && help->helper && + !strcmp(help->helper->name, helpname)) + return 0; + else + return -EBUSY; + } + if (!strcmp(helpname, "")) { if (help && help->helper) { /* we had a helper before ... */