Re: [PATCH RFC 22/38] proc: warn about entries left in /proc/net of a dying namespace

[Jan Kara]

On Mon 02-11-26 15:21:37, Christian Brauner wrote:
> proc_net_ns_exit() runs after all the other pernet exits and frees
> net->proc_net right after removing "stat" from it. An entry that some
> pernet exit forgot to remove is left with a freed ->parent, and so
> PDE_NET() hands seq_open_net() and single_open_net() a freed struct net
> when the entry is opened through a file descriptor that someone kept.
> 
> There is no such entry in the tree that we know of, but nothing would
> tell us about one either. So warn about it like remove_proc_entry()
> does for a directory that isn't empty.
> 
> Reported-by: Chris Mason <mason@xxxxxxxxxx>
> Fixes: e9720acd728a ("[NET]: Make /proc/net a symlink on /proc/self/net (v3)")
> Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>

OK, why not. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/proc/proc_net.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
> index dbcf87a257e1..df5484813d5d 100644
> --- a/fs/proc/proc_net.c
> +++ b/fs/proc/proc_net.c
> @@ -410,7 +410,13 @@ static __net_init int proc_net_ns_init(struct net *net)
>  
>  static __net_exit void proc_net_ns_exit(struct net *net)
>  {
> +	struct proc_dir_entry *left;
> +
>  	remove_proc_entry("stat", net->proc_net);
> +	/* Whatever is left still points at net->proc_net and so at net. */
> +	left = rb_entry_safe(rb_first(&net->proc_net->subdir),
> +			     struct proc_dir_entry, subdir_node);
> +	WARN(left, "/proc/net: leaking at least '%s'\n", left->name);
>  	pde_free(net->proc_net);
>  }
>  
> 
> -- 
> 2.53.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR