linux-kernel - [PATCH 0/3] auth_gss: netns refcount leaks when use-gss-proxy==1

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Date:   Wed,  1 May 2019 14:42:22 +0800
From:   Wenbin Zeng <wenbin.zeng@...il.com>
To:     viro@...iv.linux.org.uk, davem@...emloft.net, bfields@...ldses.org,
        jlayton@...nel.org, trond.myklebust@...merspace.com,
        anna.schumaker@...app.com, wenbinzeng@...cent.com,
        dsahern@...il.com, nicolas.dichtel@...nd.com, willy@...radead.org,
        edumazet@...gle.com, jakub.kicinski@...ronome.com,
        tyhicks@...onical.com, chuck.lever@...cle.com, neilb@...e.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: [PATCH 0/3] auth_gss: netns refcount leaks when use-gss-proxy==1

This patch series fixes an auth_gss bug that results in netns refcount leaks when use-gss-proxy is set to 1.

The problem was found in privileged docker containers with gssproxy service enabled and /proc/net/rpc/use-gss-proxy set to 1, the corresponding struct net->count ends up at 2 after container gets killed, the consequence is that the struct net cannot be freed.

It turns out that write_gssp() called gssp_rpc_create() to create a rpc client, this increases net->count by 2; rpcsec_gss_exit_net() is supposed to decrease net->count but it never gets called because its call-path is:
	net->count==0 -> cleanup_net -> ops_exit_list -> rpcsec_gss_exit_net
Before rpcsec_gss_exit_net() gets called, net->count cannot reach 0, this is a deadlock situation.

To fix the problem, we must break the deadlock, rpcsec_gss_exit_net() should move out of the put() path and find another chance to get called, I think nsfs_evict() is a good place to go, when netns inode gets evicted we call rpcsec_gss_exit_net() to free the rpc client, this requires a new callback i.e. evict to be added in struct proc_ns_operations, and add netns_evict() as one of netns_operations as well.

Wenbin Zeng (3):
  nsfs: add evict callback into struct proc_ns_operations
  netns: add netns_evict into netns_operations
  auth_gss: fix deadlock that blocks rpcsec_gss_exit_net when
    use-gss-proxy==1

 fs/nsfs.c                      |  2 ++
 include/linux/proc_ns.h        |  1 +
 include/net/net_namespace.h    |  1 +
 net/core/net_namespace.c       | 12 ++++++++++++
 net/sunrpc/auth_gss/auth_gss.c |  9 ++++++---
 5 files changed, 22 insertions(+), 3 deletions(-)

-- 
1.8.3.1