FAILED: patch "[PATCH] ksmbd: fix use-after-free and NULL deref in" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 2 messages Mar 29 – Mar 30

Subsystems (2)

Stable branch Kernel SMB3 server (ksmbd)

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[email protected]

author maintainer

2026-03-29 07:21 UTC #0 lore raw

The patch below does not apply to the 6.12-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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 48623ec358c1c600fa1e38368746f933e0f1a617
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026032918-refute-diameter-867a@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 48623ec358c1c600fa1e38368746f933e0f1a617 Mon Sep 17 00:00:00 2001
From: Werner Kasselman <[email protected]>
Date: Mon, 16 Mar 2026 11:38:47 +0000
Subject: [PATCH] ksmbd: fix use-after-free and NULL deref in
smb_grant_oplock()

smb_grant_oplock() has two issues in the oplock publication sequence:

1) opinfo is linked into ci->m_op_list (via opinfo_add) before add_lease_global_list() is called. If add_lease_global_list() fails (kmalloc returns NULL), the error path frees the opinfo via __free_opinfo() while it is still linked in ci->m_op_list. Concurrent m_op_list readers (opinfo_get_list, or direct iteration in smb_break_all_levII_oplock) dereference the freed node.

2) opinfo->o_fp is assigned after add_lease_global_list() publishes the opinfo on the global lease list. A concurrent find_same_lease_key() can walk the lease list and dereference opinfo->o_fp->f_ci while o_fp is still NULL.

Fix by restructuring the publication sequence to eliminate post-publish failure:

- Set opinfo->o_fp before any list publication (fixes NULL deref).
- Preallocate lease_table via alloc_lease_table() before opinfo_add() so add_lease_global_list() becomes infallible after publication.
- Keep the original m_op_list publication order (opinfo_add before lease list) so concurrent opens via same_client_has_lease() and opinfo_get_list() still see the in-flight grant.
- Use opinfo_put() instead of __free_opinfo() on err_out so that the RCU-deferred free path is used.

This also requires splitting add_lease_global_list() to take a preallocated lease_table and changing its return type from int to void, since it can no longer fail.

Fixes 1dfd062caa16 ("ksmbd: fix use-after-free by using call_rcu() for oplock_info")

Cc [email protected]

Signed-off-by Werner Kasselman <[email protected]>

Reviewed-by ChenXiaoSong <[email protected]>

Acked-by Namjae Jeon <[email protected]>

Signed-off-by Steve French <[email protected]>

fs/smb/server/oplock.c +45 ~~-27~~

index 393a4ae47cc1..9b2bb8764a80 100644
@@ -82,11 +82,19 @@ static void lease_del_list(struct oplock_info *opinfo)
 	spin_unlock(&lb->lb_lock);
 }
 
-static void lb_add(struct lease_table *lb)
+static struct lease_table *alloc_lease_table(struct oplock_info *opinfo)
 {
-	write_lock(&lease_list_lock);
-	list_add(&lb->l_entry, &lease_table_list);
-	write_unlock(&lease_list_lock);
+	struct lease_table *lb;
+
+	lb = kmalloc_obj(struct lease_table, KSMBD_DEFAULT_GFP);
+	if (!lb)
+		return NULL;
+
+	memcpy(lb->client_guid, opinfo->conn->ClientGUID,
+	       SMB2_CLIENT_GUID_SIZE);
+	INIT_LIST_HEAD(&lb->lease_list);
+	spin_lock_init(&lb->lb_lock);
+	return lb;
 }
 
 static int alloc_lease(struct oplock_info *opinfo, struct lease_ctx_info *lctx)

@@ -1042,34 +1050,27 @@ static void copy_lease(struct oplock_info *op1, struct oplock_info *op2)
 	lease2->version = lease1->version;
 }
 
-static int add_lease_global_list(struct oplock_info *opinfo)
+static void add_lease_global_list(struct oplock_info *opinfo,
+				  struct lease_table *new_lb)
 {
 	struct lease_table *lb;
 
-	read_lock(&lease_list_lock);
+	write_lock(&lease_list_lock);
 	list_for_each_entry(lb, &lease_table_list, l_entry) {
 		if (!memcmp(lb->client_guid, opinfo->conn->ClientGUID,
 			    SMB2_CLIENT_GUID_SIZE)) {
 			opinfo->o_lease->l_lb = lb;
 			lease_add_list(opinfo);
-			read_unlock(&lease_list_lock);
-			return 0;
+			write_unlock(&lease_list_lock);
+			kfree(new_lb);
+			return;
 		}
 	}
-	read_unlock(&lease_list_lock);
 
-	lb = kmalloc_obj(struct lease_table, KSMBD_DEFAULT_GFP);
-	if (!lb)
-		return -ENOMEM;
-
-	memcpy(lb->client_guid, opinfo->conn->ClientGUID,
-	       SMB2_CLIENT_GUID_SIZE);
-	INIT_LIST_HEAD(&lb->lease_list);
-	spin_lock_init(&lb->lb_lock);
-	opinfo->o_lease->l_lb = lb;
+	opinfo->o_lease->l_lb = new_lb;
 	lease_add_list(opinfo);
-	lb_add(lb);
-	return 0;
+	list_add(&new_lb->l_entry, &lease_table_list);
+	write_unlock(&lease_list_lock);
 }
 
 static void set_oplock_level(struct oplock_info *opinfo, int level,

@@ -1189,6 +1190,7 @@ int smb_grant_oplock(struct ksmbd_work *work, int req_op_level, u64 pid,
 	int err = 0;
 	struct oplock_info *opinfo = NULL, *prev_opinfo = NULL;
 	struct ksmbd_inode *ci = fp->f_ci;
+	struct lease_table *new_lb = NULL;
 	bool prev_op_has_lease;
 	__le32 prev_op_state = 0;

@@ -1291,21 +1293,37 @@ int smb_grant_oplock(struct ksmbd_work *work, int req_op_level, u64 pid,
 	set_oplock_level(opinfo, req_op_level, lctx);
 
 out:
+	/*
+	 * Set o_fp before any publication so that concurrent readers
+	 * (e.g. find_same_lease_key() on the lease list) that
+	 * dereference opinfo->o_fp don't hit a NULL pointer.
+	 *
+	 * Keep the original publication order so concurrent opens can
+	 * still observe the in-flight grant via ci->m_op_list, but make
+	 * everything after opinfo_add() no-fail by preallocating any new
+	 * lease_table first.
+	 */
+	opinfo->o_fp = fp;
+	if (opinfo->is_lease) {
+		new_lb = alloc_lease_table(opinfo);
+		if (!new_lb) {
+			err = -ENOMEM;
+			goto err_out;
+		}
+	}
+
 	opinfo_count_inc(fp);
 	opinfo_add(opinfo, fp);
 
-	if (opinfo->is_lease) {
-		err = add_lease_global_list(opinfo);
-		if (err)
-			goto err_out;
-	}
+	if (opinfo->is_lease)
+		add_lease_global_list(opinfo, new_lb);
 
 	rcu_assign_pointer(fp->f_opinfo, opinfo);
-	opinfo->o_fp = fp;
 
 	return 0;
 err_out:
-	__free_opinfo(opinfo);
+	kfree(new_lb);
+	opinfo_put(opinfo);
 	return err;
 }

Sasha Levin

maintainer

2026-03-30 23:46 UTC #1 lore raw

PATCH 1/1 ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

From: Werner Kasselman <[email protected]>

[ Upstream commit 48623ec358c1c600fa1e38368746f933e0f1a617 ]