linux-kernel - Re: [PATCH net] ipv6: addrlabel: fix possible memory leak in ip6addrlbl_net

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Date:   Mon, 23 Nov 2020 17:22:07 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Wang Hai <wanghai38@...wei.com>
Cc:     <davem@...emloft.net>, <kuznet@....inr.ac.ru>,
        <yoshfuji@...ux-ipv6.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] ipv6: addrlabel: fix possible memory leak in
 ip6addrlbl_net_init

On Sun, 22 Nov 2020 10:34:56 +0800 Wang Hai wrote:
> kmemleak report a memory leak as follows:
> 
> unreferenced object 0xffff8880059c6a00 (size 64):
>   comm "ip", pid 23696, jiffies 4296590183 (age 1755.384s)
>   hex dump (first 32 bytes):
>     20 01 00 10 00 00 00 00 00 00 00 00 00 00 00 00   ...............
>     1c 00 00 00 00 00 00 00 00 00 00 00 07 00 00 00  ................
>   backtrace:
>     [<00000000aa4e7a87>] ip6addrlbl_add+0x90/0xbb0
>     [<0000000070b8d7f1>] ip6addrlbl_net_init+0x109/0x170
>     [<000000006a9ca9d4>] ops_init+0xa8/0x3c0
>     [<000000002da57bf2>] setup_net+0x2de/0x7e0
>     [<000000004e52d573>] copy_net_ns+0x27d/0x530
>     [<00000000b07ae2b4>] create_new_namespaces+0x382/0xa30
>     [<000000003b76d36f>] unshare_nsproxy_namespaces+0xa1/0x1d0
>     [<0000000030653721>] ksys_unshare+0x3a4/0x780
>     [<0000000007e82e40>] __x64_sys_unshare+0x2d/0x40
>     [<0000000031a10c08>] do_syscall_64+0x33/0x40
>     [<0000000099df30e7>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> We should free all rules when we catch an error in ip6addrlbl_net_init().
> otherwise a memory leak will occur.
> 
> Fixes: 2a8cc6c89039 ("[IPV6] ADDRCONF: Support RFC3484 configurable address selection policy table.")
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Wang Hai <wanghai38@...wei.com>

We can simplify this function.

> diff --git a/net/ipv6/addrlabel.c b/net/ipv6/addrlabel.c
> index 642fc6ac13d2..637e323a0224 100644
> --- a/net/ipv6/addrlabel.c
> +++ b/net/ipv6/addrlabel.c
> @@ -306,6 +306,8 @@ static int ip6addrlbl_del(struct net *net,
>  /* add default label */
>  static int __net_init ip6addrlbl_net_init(struct net *net)
>  {
> +	struct ip6addrlbl_entry *p = NULL;
> +	struct hlist_node *n;
>  	int err = 0;

err does not need init

>  	int i;
>  
> @@ -320,9 +322,17 @@ static int __net_init ip6addrlbl_net_init(struct net *net)

instead of the temporary ret variable we can assign directly to err

>  					 ip6addrlbl_init_table[i].prefixlen,
>  					 0,
>  					 ip6addrlbl_init_table[i].label, 0);
> -		/* XXX: should we free all rules when we catch an error? */
> -		if (ret && (!err || err != -ENOMEM))
> +		if (ret && (!err || err != -ENOMEM)) {

this will become if (err)

>  			err = ret;
> +			goto err_ip6addrlbl_add;
> +		}
> +	}
> +	return err;

return 0;

> +err_ip6addrlbl_add:
> +	hlist_for_each_entry_safe(p, n, &net->ipv6.ip6addrlbl_table.head, list) {
> +		hlist_del_rcu(&p->list);
> +		kfree_rcu(p, rcu);
>  	}
>  	return err;
>  }