nfsd: Fix race between FREE_STATEID and LOCK

When running LTP's nfslock01 test, the Linux client can send a LOCK
and a FREE_STATEID request at the same time. The outcome is:

Frame 324    R OPEN stateid [2,O]

Frame 115004 C LOCK lockowner_is_new stateid [2,O] offset 672000 len 64
Frame 115008 R LOCK stateid [1,L]
Frame 115012 C WRITE stateid [0,L] offset 672000 len 64
Frame 115016 R WRITE NFS4_OK
Frame 115019 C LOCKU stateid [1,L] offset 672000 len 64
Frame 115022 R LOCKU NFS4_OK
Frame 115025 C FREE_STATEID stateid [2,L]
Frame 115026 C LOCK lockowner_is_new stateid [2,O] offset 672128 len 64
Frame 115029 R FREE_STATEID NFS4_OK
Frame 115030 R LOCK stateid [3,L]
Frame 115034 C WRITE stateid [0,L] offset 672128 len 64
Frame 115038 R WRITE NFS4ERR_BAD_STATEID

In other words, the server returns stateid L in a successful LOCK
reply, but it has already released it. Subsequent uses of stateid L
fail.

To address this, protect the generation check in nfsd4_free_stateid
with the st_mutex. This should guarantee that only one of two
outcomes occurs: either LOCK returns a fresh valid stateid, or
FREE_STATEID returns NFS4ERR_LOCKS_HELD.

Reported-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Fix-suggested-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 28 insertions, 12 deletions

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 8410ca275db1..0edc1822f144 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4903,6 +4903,32 @@ nfsd4_test_stateid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
         return nfs_ok;
 }
 
+static __be32
+nfsd4_free_lock_stateid(stateid_t *stateid, struct nfs4_stid *s)
+{
+        struct nfs4_ol_stateid *stp = openlockstateid(s);
+        __be32 ret;
+
+        mutex_lock(&stp->st_mutex);
+
+        ret = check_stateid_generation(stateid, &s->sc_stateid, 1);
+        if (ret)
+                goto out;
+
+        ret = nfserr_locks_held;
+        if (check_for_locks(stp->st_stid.sc_file,
+                            lockowner(stp->st_stateowner)))
+                goto out;
+
+        release_lock_stateid(stp);
+        ret = nfs_ok;
+
+out:
+        mutex_unlock(&stp->st_mutex);
+        nfs4_put_stid(s);
+        return ret;
+}
+
 __be32
 nfsd4_free_stateid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
                    struct nfsd4_free_stateid *free_stateid)
@@ -4910,7 +4936,6 @@ nfsd4_free_stateid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
         stateid_t *stateid = &free_stateid->fr_stateid;
         struct nfs4_stid *s;
         struct nfs4_delegation *dp;
-        struct nfs4_ol_stateid *stp;
         struct nfs4_client *cl = cstate->session->se_client;
         __be32 ret = nfserr_bad_stateid;
 
@@ -4929,18 +4954,9 @@ nfsd4_free_stateid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
                 ret = nfserr_locks_held;
                 break;
         case NFS4_LOCK_STID:
-                ret = check_stateid_generation(stateid, &s->sc_stateid, 1);
-                if (ret)
-                        break;
-                stp = openlockstateid(s);
-                ret = nfserr_locks_held;
-                if (check_for_locks(stp->st_stid.sc_file,
-                                    lockowner(stp->st_stateowner)))
-                        break;
-                WARN_ON(!unhash_lock_stateid(stp));
+                atomic_inc(&s->sc_count);
                 spin_unlock(&cl->cl_lock);
-                nfs4_put_stid(s);
-                ret = nfs_ok;
+                ret = nfsd4_free_lock_stateid(stateid, s);
                 goto out;
         case NFS4_REVOKED_DELEG_STID:
                 dp = delegstateid(s);