Subject: WARNING: proc registration bug in clusterip_tg_check

From: syzbot <[email-masked]>
Date: Wed, 07 Feb 2018 03:24:01 -0800

Hello,

syzbot tried to test the proposed patch but build/boot failed:

kernel build failed: failed to run /usr/bin/make [make bzImage -j 32  
CC=/syzkaller/gcc/bin/gcc]: exit status 2
scripts/kconfig/conf  --silentoldconfig Kconfig
   CHK     include/config/kernel.release
   CHK     include/generated/uapi/linux/version.h
   CHK     include/generated/utsrelease.h
   CHK     scripts/mod/devicetable-offsets.h
   CHK     include/generated/bounds.h
   CHK     include/generated/timeconst.h
   CHK     include/generated/asm-offsets.h
   CALL    scripts/checksyscalls.sh
   CHK     include/generated/compile.h
   CC      net/ipv4/netfilter/ipt_CLUSTERIP.o
   CC      net/ipv4/netfilter/ipt_MASQUERADE.o
   CC      net/ipv4/netfilter/ipt_REJECT.o
   CC      net/ipv4/netfilter/ipt_SYNPROXY.o
   CC      net/ipv4/netfilter/arp_tables.o
   CC      net/ipv4/netfilter/arpt_mangle.o
   CC      net/ipv4/netfilter/arptable_filter.o
   CC      net/ipv4/netfilter/nf_dup_ipv4.o
net/ipv4/netfilter/ipt_CLUSTERIP.c: In function ‘clusterip_config_init’:
net/ipv4/netfilter/ipt_CLUSTERIP.c:253:22: error: expected ‘;’ before ‘:’  
token
    goto err_remove_pte:
                       ^
scripts/Makefile.build:316: recipe for  
target 'net/ipv4/netfilter/ipt_CLUSTERIP.o' failed
make[3]: *** [net/ipv4/netfilter/ipt_CLUSTERIP.o] Error 1
make[3]: *** Waiting for unfinished jobs....
scripts/Makefile.build:575: recipe for target 'net/ipv4/netfilter' failed
make[2]: *** [net/ipv4/netfilter] Error 2
scripts/Makefile.build:575: recipe for target 'net/ipv4' failed
make[1]: *** [net/ipv4] Error 2
Makefile:1020: recipe for target 'net' failed
make: *** [net] Error 2

Tested on net commit
176bfb406d735655f9a69d868a7af0c3da959d51 (Tue Feb 6 16:48:40 2018 +0000)
Merge branch 'be2net-patch-set'

compiler: gcc (GCC) 7.1.1 20170620
Patch is attached.

--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -230,17 +230,6 @@ clusterip_config_init(struct net *net, const struct ipt_clusterip_tgt_info *i,
 	refcount_set(&c->refcount, 1);
 	refcount_set(&c->entries, 1);
 
-	spin_lock_bh(&cn->lock);
-	if (__clusterip_config_find(net, ip)) {
-		spin_unlock_bh(&cn->lock);
-		kfree(c);
-
-		return ERR_PTR(-EBUSY);
-	}
-
-	list_add_rcu(&c->list, &cn->configs);
-	spin_unlock_bh(&cn->lock);
-
 #ifdef CONFIG_PROC_FS
 	{
 		char buffer[16];
@@ -257,20 +246,31 @@ clusterip_config_init(struct net *net, const struct ipt_clusterip_tgt_info *i,
 	}
 #endif
 
+	spin_lock_bh(&cn->lock);
+	if (__clusterip_config_find(net, ip)) {
+		spin_unlock_bh(&cn->lock);
+		err = -EBUSY;
+		goto err_remove_pte:
+	}
+
+	list_add_rcu(&c->list, &cn->configs);
+	spin_unlock_bh(&cn->lock);
+
 	c->notifier.notifier_call = clusterip_netdev_event;
 	err = register_netdevice_notifier(&c->notifier);
 	if (!err)
 		return c;
 
+	spin_lock_bh(&cn->lock);
+	list_del_rcu(&c->list);
+	spin_unlock_bh(&cn->lock);
+
+err_remove_pte:
 #ifdef CONFIG_PROC_FS
 	proc_remove(c->pde);
 err:
 #endif
-	spin_lock_bh(&cn->lock);
-	list_del_rcu(&c->list);
-	spin_unlock_bh(&cn->lock);
 	kfree(c);
-
 	return ERR_PTR(err);
 }