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Sender: Anna Schumaker <schumakeranna@gmail.com>
From:   schumaker.anna@gmail.com
To:     Trond.Myklebust@hammerspace.com, linux-nfs@vger.kernel.org
Cc:     Anna.Schumaker@Netapp.com
Subject: [PATCH] NFS: Fix use-after-free in nfs4_init_client()
Date:   Wed,  2 Jun 2021 14:27:43 -0400
Message-Id: <20210602182743.531623-1-Anna.Schumaker@Netapp.com>
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From: Anna Schumaker <Anna.Schumaker@Netapp.com>

KASAN reports a use-after-free when attempting to mount two different
exports through two different NICs that belong to the same server.

Olga was able to hit this with kernels starting somewhere between 5.7
and 5.10, but I traced the patch that introduced the clear_bit() call to
4.13. So something must have changed in the refcounting of the clp
pointer to make this call to nfs_put_client() the very last one.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
---
 fs/nfs/nfs4client.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 889a9f4c0310..42719384e25f 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -435,8 +435,8 @@ struct nfs_client *nfs4_init_client(struct nfs_client *clp,
 		 */
 		nfs_mark_client_ready(clp, -EPERM);
 	}
-	nfs_put_client(clp);
 	clear_bit(NFS_CS_TSM_POSSIBLE, &clp->cl_flags);
+	nfs_put_client(clp);
 	return old;
 
 error:
-- 
2.29.2