nfsd: return correct openowner when there is a race to put one in the hash

[ Upstream commit c5952338bfc234e54deda45b7228f610a545e28a ]

alloc_init_open_stateowner can return an already freed entry if there is
a race to put openowners in the hashtable.

In commit 7ffb588086e9, we changed it so that we allocate and initialize
an openowner, and then check to see if a matching one got stuffed into
the hashtable in the meantime. If it did, then we free the one we just
allocated and take a reference on the one already there. There is a bug
here though. The code will then return the pointer to the one that was
allocated (and has now been freed).

This wasn't evident before as this race almost never occurred. The Linux
kernel client used to serialize requests for a single openowner.  That
has changed now with v4.0 kernels, and this race can now easily occur.

Fixes: 7ffb588086e9
Cc: <stable@vger.kernel.org> # v3.17+
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Reported-by: Christoph Hellwig <hch@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 5c9c13ee72f99e4a27d0456ea60e3d8fd1ea48c4..4296acd25f7269e4c8d4b600a9d27a58e1f23555 100644 (file)
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -3226,7 +3226,7 @@ alloc_init_open_stateowner(unsigned int strhashval, struct nfsd4_open *open,
        } else
                nfs4_free_openowner(&oo->oo_owner);
        spin_unlock(&clp->cl_lock);
-       return oo;
+       return ret;
 }
 
 static void init_open_stateid(struct nfs4_ol_stateid *stp, struct nfs4_file *fp, struct nfsd4_open *open) {