From: Liping Zhang <zlpnobody@xxxxxxxxx>
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 <zlpnobody@xxxxxxxxx>
---
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 59ee27d..7b83bbf 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, "")) {
--
2.5.5
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