ISDN: Protect ipc_head list

Make sure that the ipc_head list cannot change under us by
protecting it with a spin lock.

drivers/isdn/i4l/isdn_ppp_ccp.c

@@ -557,6 +557,7 @@ ippp_ccp_send_ccp(struct ippp_ccp *ccp, struct sk_buff *skb)
 }
 
 static LIST_HEAD(ipc_head);
+static spinlock_t ipc_head_lock;
 
 int
 ippp_ccp_set_compressor(struct ippp_ccp *ccp, int unit,
@@ -571,25 +572,28 @@ ippp_ccp_set_compressor(struct ippp_ccp *ccp, int unit,
 		printk(KERN_DEBUG "[%d] Set %scompressor type %d\n", unit,
 		       data->flags & IPPP_COMP_FLAG_XMIT ? "" : "de", num);
 
+	spin_lock(&ipc_head_lock);
 	list_for_each_entry(ipc, &ipc_head, list) {
-		if (ipc->num != num)
-			continue;
+		if (ipc->num == num &&
+		    try_module_get(ipc->owner))
+			goto found;
+	}
+	spin_unlock(&ipc_head_lock);
+	return -EINVAL;
 
-		if (!try_module_get(ipc->owner))
-			continue;
+ found:
+	spin_unlock(&ipc_head_lock);
 
 	stat = ipc->alloc(data);
 	if (!stat) {
 		printk(KERN_ERR "Can't alloc (de)compression!\n");
-			module_put(ipc->owner);
-			break;
+		goto err;
 	}
 	ret = ipc->init(stat, data, unit, 0);
 	if(!ret) {
 		printk(KERN_ERR "Can't init (de)compression!\n");
 		ipc->free(stat);
-			module_put(ipc->owner);
-			break;
+		goto err;
 	}
 	if (data->flags & IPPP_COMP_FLAG_XMIT) {
 		if (ccp->comp_stat) {
@@ -607,7 +611,9 @@ ippp_ccp_set_compressor(struct ippp_ccp *ccp, int unit,
 		ccp->decompressor = ipc;
 	}
 	return 0;
-	}
+
+ err:
+	module_put(ipc->owner);
 	return -EINVAL;
 }
 
@@ -618,25 +624,34 @@ ippp_ccp_get_compressors(unsigned long protos[8])
 	int i, j;
 
 	memset(protos, 0, sizeof(unsigned long) * 8);
+
+	spin_lock(&ipc_head_lock);
 	list_for_each_entry(ipc, &ipc_head, list) {
 		j = ipc->num / (sizeof(long)*8);
 		i = ipc->num % (sizeof(long)*8);
 		if (j < 8)
 			protos[j] |= 1 << i;
 	}
+	spin_unlock(&ipc_head_lock);
 }
 
 int
 isdn_ppp_register_compressor(struct isdn_ppp_compressor *ipc)
 {
+	spin_lock(&ipc_head_lock);
 	list_add_tail(&ipc->list, &ipc_head);
+	spin_unlock(&ipc_head_lock);
+
 	return 0;
 }
 
 int
 isdn_ppp_unregister_compressor(struct isdn_ppp_compressor *ipc)
 {
+	spin_lock(&ipc_head_lock);
 	list_del(&ipc->list);
+	spin_unlock(&ipc_head_lock);
+
 	return 0;
 }