From 3173d5b8c89e67fa3176292ff9af06f09f365348 Mon Sep 17 00:00:00 2001 From: Liping Zhang Date: Sat, 1 Apr 2017 20:55:44 +0800 Subject: [PATCH] netfilter: ctnetlink: make it safer when checking the ct helper name One CPU is doing ctnetlink_change_helper(), while another CPU is doing unhelp() at the same time. So even if help->helper is not NULL at first, the later statement strcmp(help->helper->name, ...) may still access the NULL pointer. So we must use rcu_read_lock and rcu_dereference to avoid such _bad_ thing happen. Fixes: f95d7a46bc57 ("netfilter: ctnetlink: Fix regression in CTA_HELP processing") Signed-off-by: Liping Zhang Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_netlink.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c index 06d28ac663df..f9c643bc1a8e 100644 --- a/net/netfilter/nf_conntrack_netlink.c +++ b/net/netfilter/nf_conntrack_netlink.c @@ -1488,11 +1488,16 @@ static int ctnetlink_change_helper(struct nf_conn *ct, * 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; + err = -EBUSY; + if (help) { + rcu_read_lock(); + helper = rcu_dereference(help->helper); + if (helper && !strcmp(helper->name, helpname)) + err = 0; + rcu_read_unlock(); + } + + return err; } if (!strcmp(helpname, "")) {