[PATCH] appletalk: Correctly handle return value of register_snap_client

[PATCH] appletalk: Correctly handle return value of register_snap_client

[Yue Haibing]

From: YueHaibing <yuehaibing@huawei.com>

register_snap_client may return NULL, all the callers
check it, but only print a warning. This will result in
NULL pointer dereference in unregister_snap_client and other
places.

It has always been used like this since v2.6

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
---
 include/linux/atalk.h |  2 +-
 net/appletalk/aarp.c  | 10 ++++++----
 net/appletalk/ddp.c   | 20 ++++++++++++--------
 3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/include/linux/atalk.h b/include/linux/atalk.h
index 5a90f28..0e5265a 100644
--- a/include/linux/atalk.h
+++ b/include/linux/atalk.h
@@ -108,7 +108,7 @@ static __inline__ struct elapaarp *aarp_hdr(struct sk_buff *skb)
 #define AARP_RESOLVE_TIME	(10 * HZ)
 
 extern struct datalink_proto *ddp_dl, *aarp_dl;
-extern void aarp_proto_init(void);
+extern int aarp_proto_init(void);
 
 /* Inter module exports */
 
diff --git a/net/appletalk/aarp.c b/net/appletalk/aarp.c
index 49a16ce..e047853 100644
--- a/net/appletalk/aarp.c
+++ b/net/appletalk/aarp.c
@@ -879,15 +879,17 @@ static struct notifier_block aarp_notifier = {
 
 static unsigned char aarp_snap_id[] = { 0x00, 0x00, 0x00, 0x80, 0xF3 };
 
-void __init aarp_proto_init(void)
+int __init aarp_proto_init(void)
 {
 	aarp_dl = register_snap_client(aarp_snap_id, aarp_rcv);
-	if (!aarp_dl)
-		printk(KERN_CRIT "Unable to register AARP with SNAP.\n");
+	if (!aarp_dl) {
+		pr_crit("Unable to register AARP with SNAP.\n");
+		return -ENOMEM;
+	}
 	timer_setup(&aarp_timer, aarp_expire_timeout, 0);
 	aarp_timer.expires  = jiffies + sysctl_aarp_expiry_time;
 	add_timer(&aarp_timer);
-	register_netdevice_notifier(&aarp_notifier);
+	return register_netdevice_notifier(&aarp_notifier);
 }
 
 /* Remove the AARP entries associated with a device. */
diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 795fbc6..709d254 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -1904,9 +1904,6 @@ static unsigned char ddp_snap_id[] = { 0x08, 0x00, 0x07, 0x80, 0x9B };
 EXPORT_SYMBOL(atrtr_get_dev);
 EXPORT_SYMBOL(atalk_find_dev_addr);
 
-static const char atalk_err_snap[] __initconst =
-	KERN_CRIT "Unable to register DDP with SNAP.\n";
-
 /* Called by proto.c on kernel start up */
 static int __init atalk_init(void)
 {
@@ -1921,17 +1918,22 @@ static int __init atalk_init(void)
 		goto out_proto;
 
 	ddp_dl = register_snap_client(ddp_snap_id, atalk_rcv);
-	if (!ddp_dl)
-		printk(atalk_err_snap);
+	if (!ddp_dl) {
+		pr_crit("Unable to register DDP with SNAP.\n");
+		goto out_sock;
+	}
 
 	dev_add_pack(&ltalk_packet_type);
 	dev_add_pack(&ppptalk_packet_type);
 
 	rc = register_netdevice_notifier(&ddp_notifier);
 	if (rc)
-		goto out_sock;
+		goto out_snap;
+
+	rc = aarp_proto_init();
+	if (rc)
+		goto out_dev;
 
-	aarp_proto_init();
 	rc = atalk_proc_init();
 	if (rc)
 		goto out_aarp;
@@ -1945,11 +1947,13 @@ static int __init atalk_init(void)
 	atalk_proc_exit();
 out_aarp:
 	aarp_cleanup_module();
+out_dev:
 	unregister_netdevice_notifier(&ddp_notifier);
-out_sock:
+out_snap:
 	dev_remove_pack(&ppptalk_packet_type);
 	dev_remove_pack(&ltalk_packet_type);
 	unregister_snap_client(ddp_dl);
+out_sock:
 	sock_unregister(PF_APPLETALK);
 out_proto:
 	proto_unregister(&ddp_proto);
-- 
2.7.0

Re: [PATCH] appletalk: Correctly handle return value of register_snap_client

[David Miller]

From: Yue Haibing <yuehaibing@huawei.com>
Date: Wed, 6 Mar 2019 15:27:40 +0800

> @@ -879,15 +879,17 @@ static struct notifier_block aarp_notifier = {
>  
>  static unsigned char aarp_snap_id[] = { 0x00, 0x00, 0x00, 0x80, 0xF3 };
>  
> -void __init aarp_proto_init(void)
> +int __init aarp_proto_init(void)
>  {
>  	aarp_dl = register_snap_client(aarp_snap_id, aarp_rcv);
> -	if (!aarp_dl)
> -		printk(KERN_CRIT "Unable to register AARP with SNAP.\n");
> +	if (!aarp_dl) {
> +		pr_crit("Unable to register AARP with SNAP.\n");
> +		return -ENOMEM;
> +	}
>  	timer_setup(&aarp_timer, aarp_expire_timeout, 0);
>  	aarp_timer.expires  = jiffies + sysctl_aarp_expiry_time;
>  	add_timer(&aarp_timer);
> -	register_netdevice_notifier(&aarp_notifier);
> +	return register_netdevice_notifier(&aarp_notifier);
>  }
>  

Your error paths in the caller of aarp_proto_init() do not handle the case
where aarp_dl is created by register_netdevice_notifier() fails.  You have
to unregister aarp_dl if it is non-NULL.

So your out_dev label path needs to handle aarp_dl if non-NULL.

Probably best is to jump to out_aarp: instead and make aarp_cleanup_module
able to handle partial cleanups.

Re: [PATCH] appletalk: Correctly handle return value of register_snap_client

[YueHaibing]

On 2019/3/7 2:17, David Miller wrote:
> From: Yue Haibing <yuehaibing@huawei.com>
> Date: Wed, 6 Mar 2019 15:27:40 +0800
> 
>> @@ -879,15 +879,17 @@ static struct notifier_block aarp_notifier = {
>>  
>>  static unsigned char aarp_snap_id[] = { 0x00, 0x00, 0x00, 0x80, 0xF3 };
>>  
>> -void __init aarp_proto_init(void)
>> +int __init aarp_proto_init(void)
>>  {
>>  	aarp_dl = register_snap_client(aarp_snap_id, aarp_rcv);
>> -	if (!aarp_dl)
>> -		printk(KERN_CRIT "Unable to register AARP with SNAP.\n");
>> +	if (!aarp_dl) {
>> +		pr_crit("Unable to register AARP with SNAP.\n");
>> +		return -ENOMEM;
>> +	}
>>  	timer_setup(&aarp_timer, aarp_expire_timeout, 0);
>>  	aarp_timer.expires  = jiffies + sysctl_aarp_expiry_time;
>>  	add_timer(&aarp_timer);
>> -	register_netdevice_notifier(&aarp_notifier);
>> +	return register_netdevice_notifier(&aarp_notifier);
>>  }
>>  
> 
> Your error paths in the caller of aarp_proto_init() do not handle the case
> where aarp_dl is created by register_netdevice_notifier() fails.  You have
> to unregister aarp_dl if it is non-NULL.

Thanks, will fix this.

> 
> So your out_dev label path needs to handle aarp_dl if non-NULL.
> 
> Probably best is to jump to out_aarp: instead and make aarp_cleanup_module
> able to handle partial cleanups.
> 
> .
>