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NFSD: Guard admin state-revocation walks with NFSD_NET_UP

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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 <xiaowu.417@qq.com>
Fixes: 1ac3629bf0 ("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>
This commit is contained in:
Chuck Lever 2026-06-21 12:25:51 -04:00
parent 4ae3a720f9
commit 2f3e6638ae
3 changed files with 12 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
fs/nfsd/nfs4proc.c
View File

@ -1588,10 +1588,9 @@ 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)
{

14
fs/nfsd/nfs4state.c
View File

@ -1946,10 +1946,9 @@ 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)
{
@ -2024,10 +2023,9 @@ 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)
{

6
fs/nfsd/nfsctl.c
View File

@ -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 {
@ -2424,7 +2424,7 @@ 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 {
@ -2471,7 +2471,7 @@ 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