linux-kernel - Re: [PATCH net 2/2] auth_gss: Fix deadlock that blocks rpcsec_gss_exit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 28 Sep 2021 09:49:52 -0400
From:   "bfields@...ldses.org" <bfields@...ldses.org>
To:     Trond Myklebust <trondmy@...merspace.com>
Cc:     "neilb@...e.com" <neilb@...e.com>,
        "timo@...henpieler.org" <timo@...henpieler.org>,
        "tyhicks@...onical.com" <tyhicks@...onical.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "wanghai38@...wei.com" <wanghai38@...wei.com>,
        "nicolas.dichtel@...nd.com" <nicolas.dichtel@...nd.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "jlayton@...nel.org" <jlayton@...nel.org>,
        "dsahern@...il.com" <dsahern@...il.com>,
        "christian.brauner@...ntu.com" <christian.brauner@...ntu.com>,
        "jiang.wang@...edance.com" <jiang.wang@...edance.com>,
        "anna.schumaker@...app.com" <anna.schumaker@...app.com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "cong.wang@...edance.com" <cong.wang@...edance.com>,
        "ast@...nel.org" <ast@...nel.org>,
        "kuniyu@...zon.co.jp" <kuniyu@...zon.co.jp>,
        "willy@...radead.org" <willy@...radead.org>,
        "wenbin.zeng@...il.com" <wenbin.zeng@...il.com>,
        "tom@...pey.com" <tom@...pey.com>,
        "chuck.lever@...cle.com" <chuck.lever@...cle.com>,
        "Rao.Shoaib@...cle.com" <Rao.Shoaib@...cle.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        "kolga@...app.com" <kolga@...app.com>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net 2/2] auth_gss: Fix deadlock that blocks
 rpcsec_gss_exit_net when use-gss-proxy==1

On Tue, Sep 28, 2021 at 01:30:17PM +0000, Trond Myklebust wrote:
> On Tue, 2021-09-28 at 11:14 +0800, Wang Hai wrote:
> > When use-gss-proxy is set to 1, write_gssp() creates a rpc client in
> > gssp_rpc_create(), this increases the 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
> > the 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, xprt will take a netns refcount which is not supposed
> > to be taken. Add a new flag to rpc_create_args called
> > RPC_CLNT_CREATE_NO_NET_REF for not increasing the netns refcount.
> > 
> > It is safe not to hold the netns refcount, because when
> > cleanup_net(), it
> > will hold the gssp_lock and then shut down the rpc client
> > synchronously.
> > 
> > 
> I don't like this solution at all. Adding this kind of flag is going to
> lead to problems down the road.
> 
> Is there any reason whatsoever why we need this RPC client to exist
> when there is no active knfsd server? IOW: Is there any reason why we
> shouldn't defer creating this RPC client for when knfsd starts up in
> this net namespace, and why we can't shut it down when knfsd shuts
> down?

The rpc create is done in the context of the process that writes to
/proc/net/rpc/use-gss-proxy to get the right namespaces.  I don't know
how hard it would be capture that information for a later create.

--b.