linux-kernel - [PATCH v2 0/3] auth_gss: netns refcount leaks when use-gss-proxy==1

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Message-Id: <1557470163-30071-1-git-send-email-wenbinzeng@tencent.com>
Date:   Fri, 10 May 2019 14:36:00 +0800
From:   Wenbin Zeng <wenbin.zeng@...il.com>
To:     bfields@...ldses.org, viro@...iv.linux.org.uk, davem@...emloft.net
Cc:     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,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: [PATCH v2 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.

v1->v2:
 * in nsfs_evict(), move ->evict() in front of ->put()

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