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nfs_common: fix race in NFS calls to nfsd_file_put_local() and nfsd_serv_put()

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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>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
This commit is contained in:
Mike Snitzer 2024-10-03 15:34:58 -04:00 committed by Anna Schumaker
parent a848c29e34
commit 65f2a5c366
6 changed files with 26 additions and 8 deletions
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6
fs/nfs/localio.c
View file

@ -340,7 +340,7 @@ 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);
}
@ -621,7 +621,7 @@ 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);
}
@ -672,7 +672,7 @@ 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);
}

5
fs/nfs_common/nfslocalio.c
View file

@ -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);

2
fs/nfsd/filecache.c
View file

@ -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;

2
fs/nfsd/localio.c
View file

@ -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,

4
fs/nfsd/nfssvc.c
View file

@ -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);

15
include/linux/nfslocalio.h
View file

@ -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 */