Patch "netfilter: ipt_CLUSTERIP: fix a race condition of proc file creation" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

netfilter: ipt_CLUSTERIP: fix a race condition of proc file creation

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
netfilter-ipt_clusterip-fix-a-race-condition-of-proc-file-creation.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Cong Wang <[email protected]>
Date: Wed, 7 Feb 2018 21:59:17 -0800
Subject: netfilter: ipt_CLUSTERIP: fix a race condition of proc file creation

From: Cong Wang <[email protected]>

commit b3e456fce9f51d6276e576d00271e2813c1b8b67 upstream.

There is a race condition between clusterip_config_entry_put() and clusterip_config_init(), after we release the spinlock in clusterip_config_entry_put(), a new proc file with a same IP could be created immediately since it is already removed from the configs list, therefore it triggers this warning:

------------[ cut here ]------------
proc_dir_entry 'ipt_CLUSTERIP/172.20.0.170' already registered
WARNING: CPU: 1 PID: 4152 at fs/proc/generic.c:330 proc_register+0x2a4/0x370 fs/proc/generic.c:329
Kernel panic - not syncing: panic_on_warn set ...

As a quick fix, just move the proc_remove() inside the spinlock.

---
 net/ipv4/netfilter/ipt_CLUSTERIP.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

@@ -107,12 +107,6 @@ clusterip_config_entry_put(struct net *n
 
 	local_bh_disable();
 	if (refcount_dec_and_lock(&c->entries, &cn->lock)) {
-		list_del_rcu(&c->list);
-		spin_unlock(&cn->lock);
-		local_bh_enable();
-
-		unregister_netdevice_notifier(&c->notifier);
-
 		/* In case anyone still accesses the file, the open/close
 		 * functions are also incrementing the refcount on their own,
 		 * so it's safe to remove the entry even if it's in use. */

@@ -120,6 +114,12 @@ clusterip_config_entry_put(struct net *n
 		if (cn->procdir)
 			proc_remove(c->pde);
 #endif
+		list_del_rcu(&c->list);
+		spin_unlock(&cn->lock);
+		local_bh_enable();
+
+		unregister_netdevice_notifier(&c->notifier);
+
 		return;
 	}
 	local_bh_enable();

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/netfilter-ipt_clusterip-fix-a-race-condition-of-proc-file-creation.patch