Subject: Re: [PATCH] net: Revert "fib_trie: use seq_file_net rather than seq->private"

From: David Ahern <[email-masked]>
Date: Wed, 04 Jun 2014 16:11:46 -0600

On 6/4/14, 4:02 PM, Sasha Levin wrote:
> This reverts commit 30f38d2fdd79f13fc929489f7e6e517b4a4bfe63.
>
> fib_triestat is surrounded by a big lie: while it claims that it's a
> seq_file (fib_triestat_seq_open, fib_triestat_seq_show), it isn't:
>
> 	static const struct file_operations fib_triestat_fops = {
> 	        .owner  = THIS_MODULE,
> 	        .open   = fib_triestat_seq_open,
> 	        .read   = seq_read,
> 	        .llseek = seq_lseek,
> 	        .release = single_release_net,
> 	};
>
> Yes, fib_triestat is just a regular file.
>
> A small detail (assuming CONFIG_NET_NS=y) is that while for seq_files
> you could do seq_file_net() to get the net ptr, doing so for a regular
> file would be wrong and would dereference an invalid pointer.
>
> The fib_triestat lie claimed a victim, and trying to show the file would
> be bad for the kernel. This patch just reverts the issue and fixes
> fib_triestat, which still needs a rewrite to either be a seq_file or
> stop claiming it is.

It worked fine for me.

fib_triestat_seq_open() is a wrapper to single_open_net() which sets the 
namespace as the private element (returned by get_proc_net).

If CONFIG_NETNS is not set:
- single_open_net essentially sets file->private to init_net which is 
also what is returned by seq_file_net

If CONFIG_NETNS is set, all is fine.

What am I missing?

David