Skip to contentSkip to conversation

FAILED: patch "[PATCH] NFSD: Prevent client use-after-free during blocked-lock" failed to apply to 6.18-stable tree

PATCH New [email protected] 2 participants 5 messages Sep 3 – Sep 7

Subsystems (2)
Stable branch NFS server
lore
Share & tools
lore

[email protected]

author maintainer
#0 lore raw

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 9026932ac8be4d0ae01db47f23619a98cc57b671
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090331-qualm-umbilical-2cdb@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9026932ac8be4d0ae01db47f23619a98cc57b671 Mon Sep 17 00:00:00 2001
From: Chuck Lever <[email protected]>
Date: Thu, 9 Jul 2026 13:40:30 -0400
Subject: [PATCH] NFSD: Prevent client use-after-free during blocked-lock
reaping

A bare lock owner -- its only remaining reference a blocked lock on nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but no reference keeping the client alive. When the per-net laundromat reaps such a lock, freeing the nbl drops the owner reference held through flc_owner, and the final nfs4_put_stateowner() takes the client's cl_lock. Because the laundromat detaches the nbl first, __destroy_client() no longer finds it, so a concurrent force_expire_client() can free the client before nfs4_put_stateowner() runs, dereferencing cl_lock in freed memory.

Pin the client with cl_rpc_users before dropping nn->blocked_locks_lock, and skip clients already expiring, whose blocked locks __destroy_client() frees while holding an owner reference. Take nn->client_lock outside nn->blocked_locks_lock. Every other site holds nn->blocked_locks_lock as a leaf, acquiring no further lock, so placing nn->client_lock outside it cannot form a lock-order cycle.

Fixes 7919d0a27f1e ("nfsd: add a LRU list for blocked locks")
Cc [email protected]
Reviewed-by Jeff Layton <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Chuck Lever <[email protected]>
fs/nfsd/nfs4state.c +20 -3
index 142ba7d80539..4acd02f1642c 100644
@@ -357,6 +357,16 @@ free_blocked_lock(struct nfsd4_blocked_lock *nbl)
 	kref_put(&nbl->nbl_kref, free_nbl);
 }
 
+/* A blocked lock's flc_owner is its nfs4_lockowner. */
+static struct nfs4_client *
+nbl_client(struct nfsd4_blocked_lock *nbl)
+{
+	struct nfs4_lockowner *lo;
+
+	lo = (struct nfs4_lockowner *)nbl->nbl_lock.c.flc_owner;
+	return lo->lo_owner.so_client;
+}
+
 static void
 remove_blocked_locks(struct nfs4_lockowner *lo)
 {

@@ -7591,22 +7601,29 @@ nfs4_laundromat(struct nfsd_net *nn)
 	 * indefinitely once the lock does become free.
 	 */
 	BUG_ON(!list_empty(&reaplist));
+	spin_lock(&nn->client_lock);
 	spin_lock(&nn->blocked_locks_lock);
-	while (!list_empty(&nn->blocked_locks_lru)) {
-		nbl = list_first_entry(&nn->blocked_locks_lru,
-					struct nfsd4_blocked_lock, nbl_lru);
+	list_for_each_safe(pos, next, &nn->blocked_locks_lru) {
+		nbl = list_entry(pos, struct nfsd4_blocked_lock, nbl_lru);
 		if (!state_expired(&lt, nbl->nbl_time))
 			break;
+		clp = nbl_client(nbl);
+		if (is_client_expired(clp))
+			continue;
+		atomic_inc(&clp->cl_rpc_users);
 		list_move(&nbl->nbl_lru, &reaplist);
 		list_del_init(&nbl->nbl_list);
 	}
 	spin_unlock(&nn->blocked_locks_lock);
+	spin_unlock(&nn->client_lock);
 
 	while (!list_empty(&reaplist)) {
 		nbl = list_first_entry(&reaplist,
 					struct nfsd4_blocked_lock, nbl_lru);
+		clp = nbl_client(nbl);
 		list_del_init(&nbl->nbl_lru);
 		free_blocked_lock(nbl);
+		put_client_no_renew(clp);
 	}
 #ifdef CONFIG_NFSD_V4_2_INTER_SSC
 	/* service the server-to-server copy delayed unmount list */
maintainer
#1 lore raw

PATCH 1/4 NFSD: Prevent client use-after-free during delegation revoke

From: Chuck Lever <[email protected]>

[ Upstream commit 4683ca76b3b7e5808338491c6eb3c20e6b4894d5 ]

A delegation stateid holds only a bare pointer to its owning nfs4_client and does not keep it alive. The client survives its stateids only because __destroy_client() drains cl_delegations and cl_revoked before free_client() runs.

nfs4_laundromat() breaks that invariant: it unhashes an expired delegation from cl_delegations, drops deleg_lock, then revoke_delegation() relinks it onto cl_revoked under cl_lock. In that window the delegation is on neither list, so client_has_state() can report no remaining state.

Every teardown path first requires cl_rpc_users to be zero, but the laundromat holds no such reference. A client whose recalled delegation has just timed out can therefore reach free_client() while revoke_delegation() is still about to dereference cl_lock, a use-after-free.

Pin the client with cl_rpc_users across the revoke so teardown blocks until it completes, then reap the delegation from cl_revoked. A client already expiring reaps its own, so skip it and leave the delegation on del_recall_lru.

Fixes 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED")
Cc [email protected]
Reviewed-by NeilBrown <[email protected]>
Reviewed-by Jeff Layton <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Chuck Lever <[email protected]>

[ sashal: Reduced backport -- upstream 4683ca76b3b7e touches 2 file(s), this
backport carries 1. Not backported here:
fs/nfsd/netns.h
This note is generated from the file lists only; see the resolution record for the reasoning. ]

Stable-dep-of: 9026932ac8be ("NFSD: Prevent client use-after-free during blocked-lock reaping")

Signed-off-by Sasha Levin <[email protected]>
---
 fs/nfsd/nfs4state.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
fs/nfsd/nfs4state.c +23 -0
index 48715a55df8fa..b24fc96b72fa0 100644
@@ -7052,6 +7052,7 @@ nfs4_laundromat(struct nfsd_net *nn)
 		.new_timeo = nn->nfsd4_lease
 	};
 	struct nfs4_cpntf_state *cps;
+	struct nfs4_client *clp;
 	copy_stateid_t *cps_t;
 	int i;
 

@@ -7080,6 +7081,18 @@ nfs4_laundromat(struct nfsd_net *nn)
 		dp = list_entry (pos, struct nfs4_delegation, dl_recall_lru);
 		if (!state_expired(&lt, dp->dl_time))
 			break;
+		clp = dp->dl_stid.sc_client;
+		spin_lock(&nn->client_lock);
+		if (is_client_expired(clp)) {
+			spin_unlock(&nn->client_lock);
+			continue;
+		}
+		/*
+		 * Pin without reviving: get_client_locked() would
+		 * flip a courtesy client back to NFSD4_ACTIVE.
+		 */
+		atomic_inc(&clp->cl_rpc_users);
+		spin_unlock(&nn->client_lock);
 		refcount_inc(&dp->dl_stid.sc_count);
 		unhash_delegation_locked(dp, SC_STATUS_REVOKED);
 		list_add(&dp->dl_recall_lru, &reaplist);

@@ -7088,8 +7101,18 @@ nfs4_laundromat(struct nfsd_net *nn)
 	while (!list_empty(&reaplist)) {
 		dp = list_first_entry(&reaplist, struct nfs4_delegation,
 					dl_recall_lru);
+		clp = dp->dl_stid.sc_client;
 		list_del_init(&dp->dl_recall_lru);
 		revoke_delegation(dp);
+		/*
+		 * Unpin without renewing: put_client_renew() would
+		 * renew the reaped client's lease.
+		 */
+		if (atomic_dec_and_lock(&clp->cl_rpc_users, &nn->client_lock)) {
+			if (is_client_expired(clp))
+				wake_up_all(&expiry_wq);
+			spin_unlock(&nn->client_lock);
+		}
 	}
 
 	spin_lock(&nn->client_lock);
Signature · 1 line
2.53.0
maintainer
#2 lore raw

PATCH 2/4 NFSD: Prevent client use-after-free during admin state revocation

From: Chuck Lever <[email protected]>

[ Upstream commit e270e5a0778e5bff852c8862ce9576ce70359393 ]

A stateid holds only a bare pointer to its nfs4_client; a stateid reference does not pin it. The client survives only because __destroy_client() drains its stateids before free_client() runs.

nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(), which dereferences the client to revoke a stateid and read clp->cl_minorversion. A teardown racing the dropped lock can free the client first.

Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero. force_expire_client() ignores it: once its wait for cl_rpc_users to reach zero has passed, a later pin goes unnoticed.

Under client_lock, skip a client whose cl_time is already zero -- force_expire_client() clears it there before waiting -- otherwise pin cl_rpc_users before dropping the lock. The walk then either sees the expiry and skips, or pins in time for that wait to cover the revoke.

Fixes 1c13bf9f2e3c ("nfsd: allow lock state ids to be revoked and then freed")
Cc [email protected]
Reviewed-by NeilBrown <[email protected]>
Reviewed-by Jeff Layton <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Chuck Lever <[email protected]>

Stable-dep-of: 9026932ac8be ("NFSD: Prevent client use-after-free during blocked-lock reaping")

Signed-off-by Sasha Levin <[email protected]>
---
 fs/nfsd/nfs4state.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)
fs/nfsd/nfs4state.c +20 -2
index b24fc96b72fa0..3a0b91d1c9cc3 100644
@@ -1842,13 +1842,23 @@ void nfsd4_revoke_states(struct nfsd_net *nn, struct super_block *sb)
 		struct nfs4_client *clp;
 	retry:
 		list_for_each_entry(clp, head, cl_idhash) {
-			struct nfs4_stid *stid = find_one_sb_stid(clp, sb,
-								  sc_types);
+			struct nfs4_stid *stid;
+
+			/*
+			 * force_expire_client() ignores cl_rpc_users once
+			 * its wait_event() has passed, so pinning cannot
+			 * keep an already-expiring client alive; the
+			 * expiry path revokes its states instead.
+			 */
+			if (is_client_expired(clp))
+				continue;
+			stid = find_one_sb_stid(clp, sb, sc_types);
 			if (stid) {
 				struct nfs4_ol_stateid *stp;
 				struct nfs4_delegation *dp;
 				struct nfs4_layout_stateid *ls;
 
+				atomic_inc(&clp->cl_rpc_users);
 				spin_unlock(&nn->client_lock);
 				switch (stid->sc_type) {
 				case SC_TYPE_OPEN:

@@ -1932,6 +1942,9 @@ void nfsd4_revoke_states(struct nfsd_net *nn, struct super_block *sb)
 					 */
 					nn->nfs40_last_revoke =
 						ktime_get_boottime_seconds();
+				if (atomic_dec_and_test(&clp->cl_rpc_users) &&
+				    is_client_expired(clp))
+					wake_up_all(&expiry_wq);
 				goto retry;
 			}
 		}

@@ -3218,6 +3231,11 @@ static void force_expire_client(struct nfs4_client *clp)
 
 	trace_nfsd_clid_admin_expired(&clp->cl_clientid);
 
+	/*
+	 * cl_time is cleared under client_lock before the wait so a
+	 * revocation walk pinning cl_rpc_users under it either skips
+	 * this client or is seen by this wait_event().
+	 */
 	spin_lock(&nn->client_lock);
 	clp->cl_time = 0;
 	spin_unlock(&nn->client_lock);
Signature · 1 line
2.53.0
maintainer
#3 lore raw

PATCH 3/4 NFSD: Consolidate the revocation-path client unpin

In reply to Sasha Levin

From: Chuck Lever <[email protected]>

[ Upstream commit 3308cf3f11ed23c79f9f3f90b34bbbad3e3a6ea9 ]

The client use-after-free fixes in the state-revocation paths left four open-coded copies of one idiom: drop a cl_rpc_users pin without renewing the client's lease, waking force_expire_client() when the last pin drops on a client it is tearing down. The accompanying "do not renew" rationale was documented at only one of the four sites.

put_client_renew_locked() and put_client_renew() already carry the same pin-drop logic, but they renew a non-expired client's lease and so would resurrect the client whose state is being revoked. Factor the common pin-drop into __put_client_locked(), parameterized by whether to renew. The renew helpers pass true; the new put_client_no_renew_locked() and put_client_no_renew() pass false and carry the revocation paths, which must not revive the client they are tearing down. No change in behavior.

Reviewed-by NeilBrown <[email protected]>
Reviewed-by Jeff Layton <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Chuck Lever <[email protected]>

Stable-dep-of: 9026932ac8be ("NFSD: Prevent client use-after-free during blocked-lock reaping")

Signed-off-by Sasha Levin <[email protected]>
---
 fs/nfsd/nfs4state.c | 65 ++++++++++++++++++++++++++++-----------------
 1 file changed, 40 insertions(+), 25 deletions(-)
fs/nfsd/nfs4state.c +40 -25
index 3a0b91d1c9cc3..ba42acf88afec 100644
@@ -207,18 +207,28 @@ renew_client_locked(struct nfs4_client *clp)
 	clp->cl_state = NFSD4_ACTIVE;
 }
 
+/*
+ * Finish a cl_rpc_users unpin with the client_lock held. A
+ * revocation walk clears @renew so the client whose state it is
+ * revoking is not revived; every other caller renews the lease of
+ * a still-active client.
+ */
+static void __put_client_locked(struct nfs4_client *clp, bool renew)
+{
+	if (is_client_expired(clp))
+		wake_up_all(&expiry_wq);
+	else if (renew)
+		renew_client_locked(clp);
+}
+
 static void put_client_renew_locked(struct nfs4_client *clp)
 {
 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
 
 	lockdep_assert_held(&nn->client_lock);
 
-	if (!atomic_dec_and_test(&clp->cl_rpc_users))
-		return;
-	if (!is_client_expired(clp))
-		renew_client_locked(clp);
-	else
-		wake_up_all(&expiry_wq);
+	if (atomic_dec_and_test(&clp->cl_rpc_users))
+		__put_client_locked(clp, true);
 }
 
 static void put_client_renew(struct nfs4_client *clp)

@@ -227,10 +237,27 @@ static void put_client_renew(struct nfs4_client *clp)
 
 	if (!atomic_dec_and_lock(&clp->cl_rpc_users, &nn->client_lock))
 		return;
-	if (!is_client_expired(clp))
-		renew_client_locked(clp);
-	else
-		wake_up_all(&expiry_wq);
+	__put_client_locked(clp, true);
+	spin_unlock(&nn->client_lock);
+}
+
+static void put_client_no_renew_locked(struct nfs4_client *clp)
+{
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+
+	lockdep_assert_held(&nn->client_lock);
+
+	if (atomic_dec_and_test(&clp->cl_rpc_users))
+		__put_client_locked(clp, false);
+}
+
+static void put_client_no_renew(struct nfs4_client *clp)
+{
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+
+	if (!atomic_dec_and_lock(&clp->cl_rpc_users, &nn->client_lock))
+		return;
+	__put_client_locked(clp, false);
 	spin_unlock(&nn->client_lock);
 }
 

@@ -1942,9 +1969,7 @@ void nfsd4_revoke_states(struct nfsd_net *nn, struct super_block *sb)
 					 */
 					nn->nfs40_last_revoke =
 						ktime_get_boottime_seconds();
-				if (atomic_dec_and_test(&clp->cl_rpc_users) &&
-				    is_client_expired(clp))
-					wake_up_all(&expiry_wq);
+				put_client_no_renew_locked(clp);
 				goto retry;
 			}
 		}

@@ -7047,9 +7072,7 @@ static void nfs40_clean_admin_revoked(struct nfsd_net *nn,
 				nfsd4_drop_revoked_stid(stid);
 				nfs4_put_stid(stid);
 				spin_lock(&nn->client_lock);
-				if (atomic_dec_and_test(&clp->cl_rpc_users) &&
-				    is_client_expired(clp))
-					wake_up_all(&expiry_wq);
+				put_client_no_renew_locked(clp);
 				goto retry;
 			}
 		spin_unlock(&clp->cl_lock);

@@ -7122,15 +7145,7 @@ nfs4_laundromat(struct nfsd_net *nn)
 		clp = dp->dl_stid.sc_client;
 		list_del_init(&dp->dl_recall_lru);
 		revoke_delegation(dp);
-		/*
-		 * Unpin without renewing: put_client_renew() would
-		 * renew the reaped client's lease.
-		 */
-		if (atomic_dec_and_lock(&clp->cl_rpc_users, &nn->client_lock)) {
-			if (is_client_expired(clp))
-				wake_up_all(&expiry_wq);
-			spin_unlock(&nn->client_lock);
-		}
+		put_client_no_renew(clp);
 	}
 
 	spin_lock(&nn->client_lock);
Signature · 1 line
2.53.0
maintainer
#4 lore raw

PATCH 4/4 NFSD: Prevent client use-after-free during blocked-lock reaping

In reply to Sasha Levin

From: Chuck Lever <[email protected]>

[ Upstream commit 9026932ac8be4d0ae01db47f23619a98cc57b671 ]

A bare lock owner -- its only remaining reference a blocked lock on nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but no reference keeping the client alive. When the per-net laundromat reaps such a lock, freeing the nbl drops the owner reference held through flc_owner, and the final nfs4_put_stateowner() takes the client's cl_lock. Because the laundromat detaches the nbl first, __destroy_client() no longer finds it, so a concurrent force_expire_client() can free the client before nfs4_put_stateowner() runs, dereferencing cl_lock in freed memory.

Pin the client with cl_rpc_users before dropping nn->blocked_locks_lock, and skip clients already expiring, whose blocked locks __destroy_client() frees while holding an owner reference. Take nn->client_lock outside nn->blocked_locks_lock. Every other site holds nn->blocked_locks_lock as a leaf, acquiring no further lock, so placing nn->client_lock outside it cannot form a lock-order cycle.

Fixes 7919d0a27f1e ("nfsd: add a LRU list for blocked locks")
Cc [email protected]
Reviewed-by Jeff Layton <[email protected]>
Link https://patch.msgid.link/[email protected] open here
Signed-off-by Chuck Lever <[email protected]>
Signed-off-by Sasha Levin <[email protected]>
---
 fs/nfsd/nfs4state.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)
fs/nfsd/nfs4state.c +20 -3
index ba42acf88afec..8d1f877f05d6e 100644
@@ -358,6 +358,16 @@ free_blocked_lock(struct nfsd4_blocked_lock *nbl)
 	kref_put(&nbl->nbl_kref, free_nbl);
 }
 
+/* A blocked lock's flc_owner is its nfs4_lockowner. */
+static struct nfs4_client *
+nbl_client(struct nfsd4_blocked_lock *nbl)
+{
+	struct nfs4_lockowner *lo;
+
+	lo = (struct nfs4_lockowner *)nbl->nbl_lock.c.flc_owner;
+	return lo->lo_owner.so_client;
+}
+
 static void
 remove_blocked_locks(struct nfs4_lockowner *lo)
 {

@@ -7175,22 +7185,29 @@ nfs4_laundromat(struct nfsd_net *nn)
 	 * indefinitely once the lock does become free.
 	 */
 	BUG_ON(!list_empty(&reaplist));
+	spin_lock(&nn->client_lock);
 	spin_lock(&nn->blocked_locks_lock);
-	while (!list_empty(&nn->blocked_locks_lru)) {
-		nbl = list_first_entry(&nn->blocked_locks_lru,
-					struct nfsd4_blocked_lock, nbl_lru);
+	list_for_each_safe(pos, next, &nn->blocked_locks_lru) {
+		nbl = list_entry(pos, struct nfsd4_blocked_lock, nbl_lru);
 		if (!state_expired(&lt, nbl->nbl_time))
 			break;
+		clp = nbl_client(nbl);
+		if (is_client_expired(clp))
+			continue;
+		atomic_inc(&clp->cl_rpc_users);
 		list_move(&nbl->nbl_lru, &reaplist);
 		list_del_init(&nbl->nbl_list);
 	}
 	spin_unlock(&nn->blocked_locks_lock);
+	spin_unlock(&nn->client_lock);
 
 	while (!list_empty(&reaplist)) {
 		nbl = list_first_entry(&reaplist,
 					struct nfsd4_blocked_lock, nbl_lru);
+		clp = nbl_client(nbl);
 		list_del_init(&nbl->nbl_lru);
 		free_blocked_lock(nbl);
+		put_client_no_renew(clp);
 	}
 #ifdef CONFIG_NFSD_V4_2_INTER_SSC
 	/* service the server-to-server copy delayed unmount list */
Signature · 1 line
2.53.0