[PATCH 4.7 092/186] nfsd: Fix race between FREE_STATEID and LOCK

From: Greg Kroah-Hartman
Date: Thu Aug 18 2016 - 10:35:38 EST


4.7-stable review patch. If anyone has any objections, please let me know.

------------------

From: Chuck Lever <chuck.lever@xxxxxxxxxx>

commit 42691398be08bd1fe99326911a0aa31f2c041d53 upstream.

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@xxxxxxxxxx>
Fix-suggested-by: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Tested-by: Alexey Kodanev <alexey.kodanev@xxxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/nfsd/nfs4state.c | 40 ++++++++++++++++++++++++++++------------
1 file changed, 28 insertions(+), 12 deletions(-)

--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4906,6 +4906,32 @@ nfsd4_test_stateid(struct svc_rqst *rqst
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)
@@ -4913,7 +4939,6 @@ nfsd4_free_stateid(struct svc_rqst *rqst
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;

@@ -4932,18 +4957,9 @@ nfsd4_free_stateid(struct svc_rqst *rqst
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);