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Revert "NFSD: Defer sub-object cleanup in export put callbacks"

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commit 516403d4d85607fdef3ca41d4a56b54e5566fa9a upstream.

This reverts commit 48db892356.

Commit 48db892356 ("NFSD: Defer sub-object cleanup in export
put callbacks") moved path_put() and auth_domain_put() out of
svc_export_put() and expkey_put() and behind queue_rcu_work() to
close a claimed use-after-free in e_show() and c_show() against
ex_path and ex_client->name. Discussion in [1] shows neither
the diagnosis nor the remedy survives review.

The downstream teardown of both sub-objects is already RCU-deferred.
auth_domain_put() reaches svcauth_unix_domain_release(), which frees
the unix_domain and its ->name through call_rcu(). path_put()
reaches dentry_free(), which frees the dentry through call_rcu(),
and prepend_path() is already structured to tolerate concurrent
dentry teardown. A reader in cache_seq_start_rcu() therefore
observes both sub-objects through the next grace period regardless
of whether svc_export_put() runs synchronously, so the synchronous
form was never unsafe.

The crash signature in the report cited by commit 48db892356
("NFSD: Defer sub-object cleanup in export put callbacks") has a
different root cause: a /proc/net/rpc cache file held open across
network-namespace exit lets cache_destroy_net() free cd->hash_table
while a reader is still walking it. The correct fix pins cd->net for
the open fd's lifetime and does not require any deferral inside
svc_export_put().

Meanwhile, deferring path_put() out of svc_export_put() reintroduces
the regression that commit 69d803c40e ("nfsd: Revert "nfsd:
release svc_expkey/svc_export with rcu_work"") repaired: after
"exportfs -r" drops the last cache reference, the mount reference
held through ex_path lingers in the workqueue, so a subsequent
umount fails with EBUSY.

Restore the synchronous path_put() and auth_domain_put() in
svc_export_put() and expkey_put() and the call_rcu()/kfree_rcu()
free of the containing structures. The unrelated fix for
ex_uuid/ex_stats from commit 2530766492 ("nfsd: fix UAF when
access ex_uuid or ex_stats") is preserved.

Link: https://lore.kernel.org/all/10019b42-4589-4f9f-8d5b-d8197db1ce3c@huawei.com/ [1]
Fixes: 48db892356 ("NFSD: Defer sub-object cleanup in export put callbacks")
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Alexandr Alexandrov <alexandr.alexandrov@oracle.com>
Signed-off-by: Yang Erkun <yangerkun@huawei.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Yang Erkun 2026-05-13 10:42:52 +08:00 • committed by Greg Kroah-Hartman
commit 613257f919
3 changed files with 12 additions and 66 deletions
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67
fs/nfsd/export.c
View file

@ -36,30 +36,19 @@
* second map contains a reference to the entry in the first map.
*/
static struct workqueue_struct *nfsd_export_wq;
#define EXPKEY_HASHBITS 8
#define EXPKEY_HASHMAX (1 << EXPKEY_HASHBITS)
#define EXPKEY_HASHMASK (EXPKEY_HASHMAX -1)
static void expkey_release(struct work_struct *work)
{
struct svc_expkey *key = container_of(to_rcu_work(work),
struct svc_expkey, ek_rwork);
if (test_bit(CACHE_VALID, &key->h.flags) &&
!test_bit(CACHE_NEGATIVE, &key->h.flags))
path_put(&key->ek_path);
auth_domain_put(key->ek_client);
kfree(key);
}
static void expkey_put(struct kref *ref)
{
struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
INIT_RCU_WORK(&key->ek_rwork, expkey_release);
queue_rcu_work(nfsd_export_wq, &key->ek_rwork);
if (test_bit(CACHE_VALID, &key->h.flags) &&
!test_bit(CACHE_NEGATIVE, &key->h.flags))
path_put(&key->ek_path);
auth_domain_put(key->ek_client);
kfree_rcu(key, ek_rcu);
}
static int expkey_upcall(struct cache_detail *cd, struct cache_head *h)
@ -364,13 +353,11 @@ static void export_stats_destroy(struct export_stats *stats)
EXP_STATS_COUNTERS_NUM);
}
static void svc_export_release(struct work_struct *work)
static void svc_export_release(struct rcu_head *rcu_head)
{
struct svc_export *exp = container_of(to_rcu_work(work),
struct svc_export, ex_rwork);
struct svc_export *exp = container_of(rcu_head, struct svc_export,
ex_rcu);
path_put(&exp->ex_path);
auth_domain_put(exp->ex_client);
nfsd4_fslocs_free(&exp->ex_fslocs);
export_stats_destroy(exp->ex_stats);
kfree(exp->ex_stats);
@ -382,8 +369,9 @@ static void svc_export_put(struct kref *ref)
{
struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
INIT_RCU_WORK(&exp->ex_rwork, svc_export_release);
queue_rcu_work(nfsd_export_wq, &exp->ex_rwork);
path_put(&exp->ex_path);
auth_domain_put(exp->ex_client);
call_rcu(&exp->ex_rcu, svc_export_release);
}
static int svc_export_upcall(struct cache_detail *cd, struct cache_head *h)
@ -1492,36 +1480,6 @@ const struct seq_operations nfs_exports_op = {
.show = e_show,
};
/**
* nfsd_export_wq_init - allocate the export release workqueue
*
* Called once at module load. The workqueue runs deferred svc_export and
* svc_expkey release work scheduled by queue_rcu_work() in the cache put
* callbacks.
*
* Return values:
* %0: workqueue allocated
* %-ENOMEM: allocation failed
*/
int nfsd_export_wq_init(void)
{
nfsd_export_wq = alloc_workqueue("nfsd_export", WQ_UNBOUND, 0);
if (!nfsd_export_wq)
return -ENOMEM;
return 0;
}
/**
* nfsd_export_wq_shutdown - drain and free the export release workqueue
*
* Called once at module unload. Per-namespace teardown in
* nfsd_export_shutdown() has already drained all deferred work.
*/
void nfsd_export_wq_shutdown(void)
{
destroy_workqueue(nfsd_export_wq);
}
/*
* Initialize the exports module.
*/
@ -1583,9 +1541,6 @@ nfsd_export_shutdown(struct net *net)
cache_unregister_net(nn->svc_expkey_cache, net);
cache_unregister_net(nn->svc_export_cache, net);
/* Drain deferred export and expkey release work. */
rcu_barrier();
flush_workqueue(nfsd_export_wq);
cache_destroy_net(nn->svc_expkey_cache, net);
cache_destroy_net(nn->svc_export_cache, net);
svcauth_unix_purge(net);

7
fs/nfsd/export.h
View file

@ -7,7 +7,6 @@
#include <linux/sunrpc/cache.h>
#include <linux/percpu_counter.h>
#include <linux/workqueue.h>
#include <uapi/linux/nfsd/export.h>
#include <linux/nfs4.h>
@ -76,7 +75,7 @@ struct svc_export {
u32 ex_layout_types;
struct nfsd4_deviceid_map *ex_devid_map;
struct cache_detail *cd;
struct rcu_work ex_rwork;
struct rcu_head ex_rcu;
unsigned long ex_xprtsec_modes;
struct export_stats *ex_stats;
};
@ -93,7 +92,7 @@ struct svc_expkey {
u32 ek_fsid[6];
struct path ek_path;
struct rcu_work ek_rwork;
struct rcu_head ek_rcu;
};
#define EX_ISSYNC(exp) (!((exp)->ex_flags & NFSEXP_ASYNC))
@ -111,8 +110,6 @@ __be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp,
/*
* Function declarations
*/
int nfsd_export_wq_init(void);
void nfsd_export_wq_shutdown(void);
int nfsd_export_init(struct net *);
void nfsd_export_shutdown(struct net *);
void nfsd_export_flush(struct net *);

8
fs/nfsd/nfsctl.c
View file

@ -2320,12 +2320,9 @@ static int __init init_nfsd(void)
if (retval)
goto out_free_pnfs;
nfsd_lockd_init(); /* lockd->nfsd callbacks */
retval = nfsd_export_wq_init();
if (retval)
goto out_free_lockd;
retval = register_pernet_subsys(&nfsd_net_ops);
if (retval < 0)
goto out_free_export_wq;
goto out_free_lockd;
retval = register_cld_notifier();
if (retval)
goto out_free_subsys;
@ -2354,8 +2351,6 @@ out_free_cld:
unregister_cld_notifier();
out_free_subsys:
unregister_pernet_subsys(&nfsd_net_ops);
out_free_export_wq:
nfsd_export_wq_shutdown();
out_free_lockd:
nfsd_lockd_shutdown();
nfsd_drc_slab_free();
@ -2376,7 +2371,6 @@ static void __exit exit_nfsd(void)
nfsd4_destroy_laundry_wq();
unregister_cld_notifier();
unregister_pernet_subsys(&nfsd_net_ops);
nfsd_export_wq_shutdown();
nfsd_drc_slab_free();
nfsd_lockd_shutdown();
nfsd4_free_slabs();