linux-kernel - [PATCH] SUNRPC: fix use-after-free in rpc_free_client

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Message-ID: <87r1vuazm0.fsf@notabene.neil.brown.name>
Date:   Sat, 09 May 2020 07:25:11 +1000
From:   NeilBrown <neilb@...e.de>
To:     syzbot <syzbot+22b5ef302c7c40d94ea8@...kaller.appspotmail.com>,
        anna.schumaker@...app.com, bfields@...ldses.org,
        chuck.lever@...cle.com, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        trond.myklebust@...merspace.com
Subject: [PATCH] SUNRPC: fix use-after-free in rpc_free_client_work()


Parts of rpc_free_client() were recently moved to
a separate rpc_free_clent_work().  This introduced
a use-after-free as rpc_clnt_remove_pipedir() calls
rpc_net_ns(), and that uses clnt->cl_xprt which has already
been freed.
So move the call to xprt_put() after the call to
rpc_clnt_remove_pipedir().

Reported-by: syzbot+22b5ef302c7c40d94ea8@...kaller.appspotmail.com
Fixes: 7c4310ff5642 ("SUNRPC: defer slow parts of rpc_free_client() to a workqueue.")
Signed-off-by: NeilBrown <neilb@...e.de>
---
 net/sunrpc/clnt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 8350d3a2e9a7..8d3972ea688b 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -890,6 +890,7 @@ static void rpc_free_client_work(struct work_struct *work)
 	 */
 	rpc_clnt_debugfs_unregister(clnt);
 	rpc_clnt_remove_pipedir(clnt);
+	xprt_put(rcu_dereference_raw(clnt->cl_xprt));
 
 	kfree(clnt);
 	rpciod_down();
@@ -907,7 +908,6 @@ rpc_free_client(struct rpc_clnt *clnt)
 	rpc_unregister_client(clnt);
 	rpc_free_iostats(clnt->cl_metrics);
 	clnt->cl_metrics = NULL;
-	xprt_put(rcu_dereference_raw(clnt->cl_xprt));
 	xprt_iter_destroy(&clnt->cl_xpi);
 	put_cred(clnt->cl_cred);
 	rpc_free_clid(clnt);
-- 
2.26.2


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