linux-kernel - [PATCH net 1/2] net: Modify unix_stream_connect to not reference count the netns of kernel sockets

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Date:   Tue, 28 Sep 2021 11:14:39 +0800
From:   Wang Hai <wanghai38@...wei.com>
To:     <bfields@...ldses.org>, <davem@...emloft.net>, <kuba@...nel.org>,
        <wenbin.zeng@...il.com>, <jlayton@...nel.org>, <dsahern@...il.com>,
        <nicolas.dichtel@...nd.com>, <viro@...iv.linux.org.uk>,
        <willy@...radead.org>, <jakub.kicinski@...ronome.com>,
        <tyhicks@...onical.com>, <cong.wang@...edance.com>,
        <ast@...nel.org>, <jiang.wang@...edance.com>,
        <christian.brauner@...ntu.com>, <edumazet@...gle.com>,
        <Rao.Shoaib@...cle.com>, <kuniyu@...zon.co.jp>,
        <trond.myklebust@...merspace.com>, <anna.schumaker@...app.com>,
        <chuck.lever@...cle.com>, <neilb@...e.com>, <kolga@...app.com>,
        <timo@...henpieler.org>, <tom@...pey.com>
CC:     <linux-nfs@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH net 1/2] net: Modify unix_stream_connect to not reference count the netns of kernel sockets

When use-gss-proxy is set to 1, write_gssp() creates a rpc client in
gssp_rpc_create(), this increases netns refcount by 2, these refcounts
are supposed to be released in rpcsec_gss_exit_net(), but it will never
happen because rpcsec_gss_exit_net() is triggered only when netns
refcount gets to 0, specifically:
    refcount=0 -> cleanup_net() -> ops_exit_list -> rpcsec_gss_exit_net
It is a deadlock situation here, refcount will never get to 0 unless
rpcsec_gss_exit_net() is called. So, in this case, the netns refcount
should not be increased.

In this case, kernel_connect()->unix_stream_connect() will take a netns
refcount. According to commit 26abe14379f8 ("net: Modify sk_alloc to not
reference count the netns of kernel sockets."), kernel sockets should not
take the netns refcount, so unix_stream_connect() should not take
the netns refcount when the sock is a kernel socket either.

Signed-off-by: Wang Hai <wanghai38@...wei.com>
---
 net/unix/af_unix.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 92345c9bb60c..af6ba67779c8 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1317,7 +1317,8 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 	err = -ENOMEM;
 
 	/* create new sock for complete connection */
-	newsk = unix_create1(sock_net(sk), NULL, 0, sock->type);
+	newsk = unix_create1(sock_net(sk), NULL,
+			     !sk->sk_net_refcnt, sock->type);
 	if (newsk == NULL)
 		goto out;
 
-- 
2.17.1