[6.12-rc2 v2 PATCH 1/7] nfs_common: fix race in NFS calls to nfsd_file_put_local() and nfsd_serv_put()

Mike Snitzer
2024-10-03T19:35:07Z

Add nfs_to_nfsd_file_put_local() interface to fix race with nfsd
module unload. Similarly, use RCU around nfs_open_local_fh()'s error
path call to nfs_to->nfsd_serv_put(). Holding RCU ensures that NFS
will safely _call and return_ from its nfs_to calls into the NFSD
functions nfsd_file_put_local() and nfsd_serv_put().

Otherwise, if RCU isn't used then there is a narrow window when NFS's
reference for the nfsd_file and nfsd_serv are dropped and the NFSD
module could be unloaded, which could result in a crash from the
return instruction for either nfs_to->nfsd_file_put_local() or
nfs_to->nfsd_serv_put().

Reported-by: NeilBrown <neilb@suse.de>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
fs/nfs/localio.c | 6 +++---
fs/nfs_common/nfslocalio.c | 5 ++++-
fs/nfsd/filecache.c | 2 +-
fs/nfsd/localio.c | 2 +-
fs/nfsd/nfssvc.c | 4 ++--
include/linux/nfslocalio.h | 15 +++++++++++++++
6 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c
index c29cdf51c458..d124c265b8fd 100644
--- a/fs/nfs/localio.c
+++ b/fs/nfs/localio.c
@@ -341,7 +341,7 @@ nfs_local_pgio_release(struct nfs_local_kiocb *iocb)
{
struct nfs_pgio_header *hdr = iocb->hdr;

- nfs_to->nfsd_file_put_local(iocb->localio);
+ nfs_to_nfsd_file_put_local(iocb->localio);
nfs_local_iocb_free(iocb);
nfs_local_hdr_release(hdr, hdr->task.tk_ops);
}
@@ -622,7 +622,7 @@ int nfs_local_doio(struct nfs_client *clp, struct nfsd_file *localio,
}
out:
if (status != 0) {
- nfs_to->nfsd_file_put_local(localio);
+ nfs_to_nfsd_file_put_local(localio);
hdr->task.tk_status = status;
nfs_local_hdr_release(hdr, call_ops);
}
@@ -673,7 +673,7 @@ nfs_local_release_commit_data(struct nfsd_file *localio,
struct nfs_commit_data *data,
const struct rpc_call_ops *call_ops)
{
- nfs_to->nfsd_file_put_local(localio);
+ nfs_to_nfsd_file_put_local(localio);
call_ops->rpc_call_done(&data->task, data);
call_ops->rpc_release(data);
}
diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c
index 42b479b9191f..5c8ce5066c16 100644
--- a/fs/nfs_common/nfslocalio.c
+++ b/fs/nfs_common/nfslocalio.c
@@ -142,8 +142,11 @@ struct nfsd_file *nfs_open_local_fh(nfs_uuid_t *uuid,
/* We have an implied reference to net thanks to nfsd_serv_try_get */
localio = nfs_to->nfsd_open_local_fh(net, uuid->dom, rpc_clnt,
cred, nfs_fh, fmode);
- if (IS_ERR(localio))
+ if (IS_ERR(localio)) {
+ rcu_read_lock();
nfs_to->nfsd_serv_put(net);
+ rcu_read_unlock();
+ }
return localio;
}
EXPORT_SYMBOL_GPL(nfs_open_local_fh);
diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 19bb88c7eebd..53070e1de3d9 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -398,7 +398,7 @@ nfsd_file_put(struct nfsd_file *nf)
* reference to the associated nn->nfsd_serv.
*/
void
-nfsd_file_put_local(struct nfsd_file *nf)
+nfsd_file_put_local(struct nfsd_file *nf) __must_hold(rcu)
{
struct net *net = nf->nf_net;

diff --git a/fs/nfsd/localio.c b/fs/nfsd/localio.c
index 291e9c69cae4..f441cb9f74d5 100644
--- a/fs/nfsd/localio.c
+++ b/fs/nfsd/localio.c
@@ -53,7 +53,7 @@ void nfsd_localio_ops_init(void)
*
* On successful return, returned nfsd_file will have its nf_net member
* set. Caller (NFS client) is responsible for calling nfsd_serv_put and
- * nfsd_file_put (via nfs_to->nfsd_file_put_local).
+ * nfsd_file_put (via nfs_to_nfsd_file_put_local).
*/
struct nfsd_file *
nfsd_open_local_fh(struct net *net, struct auth_domain *dom,
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index e236135ddc63..47172b407be8 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -214,14 +214,14 @@ int nfsd_minorversion(struct nfsd_net *nn, u32 minorversion, enum vers_op change
return 0;
}

-bool nfsd_serv_try_get(struct net *net)
+bool nfsd_serv_try_get(struct net *net) __must_hold(rcu)
{
struct nfsd_net *nn = net_generic(net, nfsd_net_id);

return (nn && percpu_ref_tryget_live(&nn->nfsd_serv_ref));
}

-void nfsd_serv_put(struct net *net)
+void nfsd_serv_put(struct net *net) __must_hold(rcu)
{
struct nfsd_net *nn = net_generic(net, nfsd_net_id);

diff --git a/include/linux/nfslocalio.h b/include/linux/nfslocalio.h
index b353abe00357..b0dd9b1eef4f 100644
--- a/include/linux/nfslocalio.h
+++ b/include/linux/nfslocalio.h
@@ -65,10 +65,25 @@ struct nfsd_file *nfs_open_local_fh(nfs_uuid_t *,
struct rpc_clnt *, const struct cred *,
const struct nfs_fh *, const fmode_t);

+static inline void nfs_to_nfsd_file_put_local(struct nfsd_file *localio)
+{
+ /*
+ * Once reference to nfsd_serv is dropped, NFSD could be
+ * unloaded, so ensure safe return from nfsd_file_put_local()
+ * by always taking RCU.
+ */
+ rcu_read_lock();
+ nfs_to->nfsd_file_put_local(localio);
+ rcu_read_unlock();
+}
+
#else /* CONFIG_NFS_LOCALIO */
static inline void nfsd_localio_ops_init(void)
{
}
+static inline void nfs_to_nfsd_file_put_local(struct nfsd_file *localio)
+{
+}
#endif /* CONFIG_NFS_LOCALIO */

#endif /* __LINUX_NFSLOCALIO_H */
--
2.44.0