Re: [net/netlink] Question about potential memleak in netlink_proto_init()

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Chenyuan Yang <chenyuan0y@gmail.com>
Date: Thu, 14 Mar 2024 19:47:18 -0500
> Dear Netlink Developers,
> 
> We are curious whether the function `netlink_proto_init()` might have a memory leak.
> 
> The function is https://elixir.bootlin.com/linux/v6.8/source/net/netlink/af_netlink.c#L2908
> and the relevant code is
> ```
> static int __init netlink_proto_init(void)
> {
> 	int i;
>   ...
> 
> 	for (i = 0; i < MAX_LINKS; i++) {
> 		if (rhashtable_init(&nl_table[i].hash,
> 				    &netlink_rhashtable_params) < 0) {
> 			while (--i > 0)
> 				rhashtable_destroy(&nl_table[i].hash);
> 			kfree(nl_table);
> 			goto panic;

If rhashtable_init() fails, the kernel panic occurs, so there's
no real memleak issue.


> 		}
> 	}
>   ...
> }
> ```
> 
> In the for loop, when `rhashtable_init()` fails, the function will free
> the allocated memory for `nl_table[i].hash` by checking `while (--i > 0)`.
> However, the first element (`i=1`) of `nl_table` is not freed since `i` is
> decremented before the check.
> 
> Based on our understanding, a possible fix would be
> ```
> -      while (--i > 0)
> +      while (--i >= 0)
> ```

Change itself looks good, no need for cleanup in the first place though.