NFS: Beware when dereferencing the delegation cred
When we look up the delegation cred, we are usually doing so in
conjunction with a read of the stateid, and we want to ensure
that the look up is atomic with that read.
Fixes: 57f188e04773 ("NFSv4: nfs_update_inplace_delegation() should update delegation cred")
[sfr@canb.auug.org.au: Fixed up borken Fixes: line from Trond :-)]
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 01974f17..816e142 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -1243,8 +1243,10 @@ static int nfs_server_reap_expired_delegations(struct nfs_server *server,
inode = nfs_delegation_grab_inode(delegation);
if (inode == NULL)
goto restart_locked;
+ spin_lock(&delegation->lock);
cred = get_cred_rcu(delegation->cred);
nfs4_stateid_copy(&stateid, &delegation->stateid);
+ spin_unlock(&delegation->lock);
clear_bit(NFS_DELEGATION_TEST_EXPIRED, &delegation->flags);
rcu_read_unlock();
nfs_delegation_test_free_expired(inode, &stateid, cred);
@@ -1363,11 +1365,14 @@ bool nfs4_copy_delegation_stateid(struct inode *inode, fmode_t flags,
{
struct nfs_inode *nfsi = NFS_I(inode);
struct nfs_delegation *delegation;
- bool ret;
+ bool ret = false;
flags &= FMODE_READ|FMODE_WRITE;
rcu_read_lock();
delegation = rcu_dereference(nfsi->delegation);
+ if (!delegation)
+ goto out;
+ spin_lock(&delegation->lock);
ret = nfs4_is_valid_delegation(delegation, flags);
if (ret) {
nfs4_stateid_copy(dst, &delegation->stateid);
@@ -1375,6 +1380,8 @@ bool nfs4_copy_delegation_stateid(struct inode *inode, fmode_t flags,
if (cred)
*cred = get_cred(delegation->cred);
}
+ spin_unlock(&delegation->lock);
+out:
rcu_read_unlock();
return ret;
}
