[PATCH 7.2.y 4/4] NFSD: Guard admin state-revocation walks with NFSD_NET_UP
From: Sasha Levin <sashal@kernel.org>
Date: 2026-09-06 13:28:50
Subsystem:
filesystems (vfs and infrastructure), kernel nfsd, sunrpc, and lockd servers, the rest · Maintainers:
Alexander Viro, Christian Brauner, Chuck Lever, Jeff Layton, Linus Torvalds
From: Chuck Lever <cel@kernel.org>
[ Upstream commit 2f3e6638aebc0ab8afb8b4e9816ea9a1cad85378 ]
Writing to /proc/fs/nfsd/unlock_filesystem, or sending the
NFSD_CMD_UNLOCK_FILESYSTEM or NFSD_CMD_UNLOCK_EXPORT netlink command,
walks the NFSv4 client hash tables to revoke open state and cancel
async COPY operations. All three handlers gate that walk on
nn->nfsd_serv, but a listener added via portlist or netlink
listener_set sets nn->nfsd_serv before any nfsd thread starts.
nfsd_startup_net() has not yet allocated nn->conf_id_hashtbl, so the
walkers dereference a NULL table. A local administrator with
CAP_SYS_ADMIN can crash the kernel this way without ever starting the
server.
nn->nfsd_serv is set when the service is created, which precedes
table allocation. NFSD_NET_UP instead brackets the window where the
tables are live: set at the end of nfsd_startup_net() and cleared in
nfsd_shutdown_net() after they are freed, both under nfsd_mutex.
Gating the three unlock paths on NFSD_NET_UP fixes the startup-time
NULL dereference while preserving the earlier post-shutdown
use-after-free fix.
Reported-by: XIAO WU <redacted>
Fixes: 1ac3629bf012 ("nfsd: prepare for supporting admin-revocation of state")
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260621162551.2469460-1-cel@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfsd/nfs4proc.c | 7 +++----
fs/nfsd/nfs4state.c | 14 ++++++--------
fs/nfsd/nfsctl.c | 6 +++---
3 files changed, 12 insertions(+), 15 deletions(-)
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 10e76bafabf29..290d0a5305c13 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c@@ -1563,10 +1563,9 @@ static bool nfsd4_copy_on_sb(const struct nfsd4_copy *copy, * @net: net namespace containing the copy operations * @sb: targeted superblock * - * Context: Caller must hold nfsd_mutex with nn->nfsd_serv confirmed - * non-NULL. nfs4_state_destroy_net() frees conf_id_hashtbl - * at server shutdown without clearing the pointer, so a - * walk without these guarantees iterates freed slab memory. + * Context: Caller must hold nfsd_mutex with NFSD_NET_UP set. Outside + * that window nn->conf_id_hashtbl is unallocated or freed, + * so the walk would dereference a NULL or dangling pointer. */ void nfsd4_cancel_copy_by_sb(struct net *net, struct super_block *sb) {
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index efa234eb6a605..0ca816553a62b 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c@@ -1876,10 +1876,9 @@ static void revoke_one_stid(struct nfsd_net *nn, struct nfs4_client *clp, * The clients which own the states will subsequently be notified that the * states have been "admin-revoked". * - * Context: Caller must hold nfsd_mutex with nn->nfsd_serv confirmed - * non-NULL. nfs4_state_destroy_net() frees conf_id_hashtbl - * at server shutdown without clearing the pointer, so a - * walk without these guarantees iterates freed slab memory. + * Context: Caller must hold nfsd_mutex with NFSD_NET_UP set. Outside + * that window nn->conf_id_hashtbl is unallocated or freed, + * so the walk would dereference a NULL or dangling pointer. */ void nfsd4_revoke_states(struct nfsd_net *nn, struct super_block *sb) {
@@ -1954,10 +1953,9 @@ static struct nfs4_stid *find_one_export_stid(struct nfs4_client *clp, * Userspace (exportfs -u) sends this after removing the last client * for a path, enabling the underlying filesystem to be unmounted. * - * Context: Caller must hold nfsd_mutex with nn->nfsd_serv confirmed - * non-NULL. nfs4_state_destroy_net() frees conf_id_hashtbl - * at server shutdown without clearing the pointer, so a - * walk without these guarantees iterates freed slab memory. + * Context: Caller must hold nfsd_mutex with NFSD_NET_UP set. Outside + * that window nn->conf_id_hashtbl is unallocated or freed, + * so the walk would dereference a NULL or dangling pointer. */ void nfsd4_revoke_export_states(struct nfsd_net *nn, const struct path *path) {
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 32106d223a23c..02abd499a4e9f 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c@@ -299,7 +299,7 @@ static ssize_t write_unlock_fs(struct file *file, char *buf, size_t size) error = nlmsvc_unlock_all_by_sb(path.dentry->d_sb); mutex_lock(&nfsd_mutex); nn = net_generic(netns(file), nfsd_net_id); - if (nn->nfsd_serv) { + if (test_bit(NFSD_NET_UP, &nn->flags)) { nfsd4_cancel_copy_by_sb(netns(file), path.dentry->d_sb); nfsd4_revoke_states(nn, path.dentry->d_sb); } else {
@@ -2344,7 +2344,7 @@ int nfsd_nl_unlock_filesystem_doit(struct sk_buff *skb, error = nlmsvc_unlock_all_by_sb(path.dentry->d_sb); mutex_lock(&nfsd_mutex); - if (nn->nfsd_serv) { + if (test_bit(NFSD_NET_UP, &nn->flags)) { nfsd4_cancel_copy_by_sb(net, path.dentry->d_sb); nfsd4_revoke_states(nn, path.dentry->d_sb); } else {
@@ -2391,7 +2391,7 @@ int nfsd_nl_unlock_export_doit(struct sk_buff *skb, struct genl_info *info) return error; mutex_lock(&nfsd_mutex); - if (nn->nfsd_serv) { + if (test_bit(NFSD_NET_UP, &nn->flags)) { nfsd_file_close_export(net, &path); nfsd4_revoke_export_states(nn, &path); } else
--
2.53.0