Re: [PATCH 1/3] sunrpc: check that domain table is empty at module unload.

[Chuck Lever <chuck.lever@oracle.com>]

Hi Neil!

Thanks for the patches. Seems to me like a good fix overall.

Judging by the syzbot e-mail, you might be posting a refresh of this
patch series, so I proffer a few minor review comments below.


> On May 20, 2020, at 11:21 PM, NeilBrown <neilb@suse.de> wrote:
> 
> The domain table should be empty at module unload.  If it isn't there is
> a bug somewhere.  So check and report.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206651
> Cc: stable@vger.kernel.org
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
> net/sunrpc/sunrpc.h      |    1 +
> net/sunrpc/sunrpc_syms.c |    2 ++
> net/sunrpc/svcauth.c     |   18 ++++++++++++++++++
> 3 files changed, 21 insertions(+)
> 
> diff --git a/net/sunrpc/sunrpc.h b/net/sunrpc/sunrpc.h
> index 47a756503d11..f6fe2e6cd65a 100644
> --- a/net/sunrpc/sunrpc.h
> +++ b/net/sunrpc/sunrpc.h
> @@ -52,4 +52,5 @@ static inline int sock_is_loopback(struct sock *sk)
> 
> int rpc_clients_notifier_register(void);
> void rpc_clients_notifier_unregister(void);
> +void auth_domain_cleanup(void);
> #endif /* _NET_SUNRPC_SUNRPC_H */
> diff --git a/net/sunrpc/sunrpc_syms.c b/net/sunrpc/sunrpc_syms.c
> index f9edaa9174a4..236fadc4a439 100644
> --- a/net/sunrpc/sunrpc_syms.c
> +++ b/net/sunrpc/sunrpc_syms.c
> @@ -23,6 +23,7 @@
> #include <linux/sunrpc/rpc_pipe_fs.h>
> #include <linux/sunrpc/xprtsock.h>
> 
> +#include "sunrpc.h"
> #include "netns.h"
> 
> unsigned int sunrpc_net_id;
> @@ -131,6 +132,7 @@ cleanup_sunrpc(void)
> 	unregister_rpc_pipefs();
> 	rpc_destroy_mempool();
> 	unregister_pernet_subsys(&sunrpc_net_ops);
> +	auth_domain_cleanup();
> #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
> 	rpc_unregister_sysctl();
> #endif
> diff --git a/net/sunrpc/svcauth.c b/net/sunrpc/svcauth.c
> index 552617e3467b..477890e8b9d8 100644
> --- a/net/sunrpc/svcauth.c
> +++ b/net/sunrpc/svcauth.c
> @@ -205,3 +205,21 @@ struct auth_domain *auth_domain_find(char *name)
> 	return NULL;
> }
> EXPORT_SYMBOL_GPL(auth_domain_find);
> +
> +void auth_domain_cleanup(void)
> +{
> +	/* There should be no auth_domains left at module unload */

Since this is a globally-visible function, could you move this comment
into a Doxy documenting comment before the function? It should make clear
that the purpose of this function is only for debugging.


> +	int h;
> +	bool found = false;
> +
> +	for (h = 0; h < DN_HASHMAX; h++) {
> +		struct auth_domain *hp;
> +
> +		hlist_for_each_entry(hp, auth_domain_table+h, hash) {
> +			found = true;
> +			printk(KERN_WARNING "sunrpc: domain %s still present at module unload.\n",
> +			       hp->name);

Nit: Documentation/process/coding-style.rst recommends using the pr_warn()
macro here (and equivalents in other patches)... And note that "svc:" is
the conventional prefix for server-side warnings.

I'm wondering... is it safe to release an auth_domain here if one is found,
so that it is not actually orphaned? The warning is information for
developers; there's nothing, say, an administrator can do about this
situation.


> +		}
> +	}
> +	WARN(found, "sunrpc: auth_domain_table not clean -> memory leak\n");

Not sure a stack trace in addition to the above warning messages adds
relevant information. Can you provide a little justification for that?

Thanks!


> +}
> 
> 

--
Chuck Lever