Re: [PATCH v2] nbd: Fix memory leak in nbd_add_socket

Re: [PATCH v2] nbd: Fix memory leak in nbd_add_socket

[Markus Elfring]

> If we add first socket to nbd, config->socks is malloced but
> num_connections does not update(nsock's allocation fail), the memory
> is leaked. Cause in later nbd_config_put(), will only free config->socks
> when num_connections is not 0.
>
> Let nsock's allocation first to avoid this.

I suggest to improve this change description.
Can an other wording variant be nicer?


…
> +++ b/drivers/block/nbd.c
> @@ -1037,21 +1037,22 @@  static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
>  		return -EBUSY;
>  	}
>
> +	nsock = kzalloc(sizeof(struct nbd_sock), GFP_KERNEL);

Please use the following code variant.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst?id=4333a9b0b67bb4e8bcd91bdd80da80b0ec151162#n854

+	nsock = kzalloc(sizeof(*nsock), GFP_KERNEL);


…
>  	if (!socks) {
>  		sockfd_put(sock);
> +		kfree(nsock);
>  		return -ENOMEM;
>  	}

Please take another software design possibility into account.

 	if (!socks) {
-		sockfd_put(sock);
-		return -ENOMEM;
+		kfree(nsock);
+		goto put_socket;
 	}


Regards,
Markus

Re: [PATCH v2] nbd: Fix memory leak in nbd_add_socket

[Zhengbin (OSKernel)]

On 2020/6/20 20:05, Markus Elfring wrote:
>> If we add first socket to nbd, config->socks is malloced but
>> num_connections does not update(nsock's allocation fail), the memory
>> is leaked. Cause in later nbd_config_put(), will only free config->socks
>> when num_connections is not 0.
>>
>> Let nsock's allocation first to avoid this.
> I suggest to improve this change description.
> Can an other wording variant be nicer?

em, how about this?


When adding first socket to nbd, if nsock's allocation fails, config->socks

is malloced but num_connections does not update, memory leak will 
occur(Function

nbd_config_put will only free config->socks when num_connections is not 0).

>
>
> …
>> +++ b/drivers/block/nbd.c
>> @@ -1037,21 +1037,22 @@  static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
>>   		return -EBUSY;
>>   	}
>>
>> +	nsock = kzalloc(sizeof(struct nbd_sock), GFP_KERNEL);
> Please use the following code variant.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst?idC33a9b0b67bb4e8bcd91bdd80da80b0ec151162#n854
>
> +	nsock = kzalloc(sizeof(*nsock), GFP_KERNEL);
>
>
> …
>>   	if (!socks) {
>>   		sockfd_put(sock);
>> +		kfree(nsock);
>>   		return -ENOMEM;
>>   	}
> Please take another software design possibility into account.
>
>   	if (!socks) {
> -		sockfd_put(sock);
> -		return -ENOMEM;
> +		kfree(nsock);
> +		goto put_socket;
>   	}
>
>
> Regards,
> Markus
>
> .
>

Re: [PATCH v2] nbd: Fix memory leak in nbd_add_socket

[Markus Elfring]

>> Can an other wording variant be nicer?
>
> em, how about this?
>
>
> When adding first socket to nbd,

How do you think about to replace abbreviations by terms?


> if nsock's allocation fails,

… failed,


> config->socks is malloced

The data structure member “config->socks” was reallocated.


> but num_connections does not update,

But the data structure member “config->num_connections” was not updated.


> memory leak will occur(Function
> nbd_config_put will only free config->socks when num_connections is not 0).

A memory leak will occur then because the function “nbd_config_put”
will free “config->socks” only when “num_connections” is not zero.

Would you like to add an imperative wording to the commit message?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=625d3449788f85569096780592549d0340e9c0c7#n151

Regards,
Markus