linux-kernel - [PATCH 6.6.y] ksmbd: fix use-after-free in ksmbd_session_rpc

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Message-Id: <20260127083149.3344689-1-1468888505@139.com>
Date: Tue, 27 Jan 2026 16:31:49 +0800
From: Li hongliang <1468888505@....com>
To: gregkh@...uxfoundation.org,
	stable@...r.kernel.org,
	linkinjeon@...nel.org
Cc: patches@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	sfrench@...ba.org,
	senozhatsky@...omium.org,
	tom@...pey.com,
	sujana.subramaniam@....com,
	sashal@...nel.org,
	linux-cifs@...r.kernel.org,
	norbert@...ensec.com,
	stfrench@...rosoft.com
Subject: [PATCH 6.6.y] ksmbd: fix use-after-free in ksmbd_session_rpc_open

From: Namjae Jeon <linkinjeon@...nel.org>

[ Upstream commit a1f46c99d9ea411f9bf30025b912d881d36fc709 ]

A UAF issue can occur due to a race condition between
ksmbd_session_rpc_open() and __session_rpc_close().
Add rpc_lock to the session to protect it.

Cc: stable@...r.kernel.org
Reported-by: Norbert Szetei <norbert@...ensec.com>
Tested-by: Norbert Szetei <norbert@...ensec.com>
Signed-off-by: Namjae Jeon <linkinjeon@...nel.org>
Signed-off-by: Steve French <stfrench@...rosoft.com>
[ KSMBD_DEFAULT_GFP is introduced by commit 0066f623bce8 ("ksmbd: use __GFP_RETRY_MAYFAIL")
 after linux-6.13. Here we still use GFP_KERNEL. ]
Signed-off-by: Li hongliang <1468888505@....com>
---
 fs/smb/server/mgmt/user_session.c | 20 ++++++++++++++------
 fs/smb/server/mgmt/user_session.h |  1 +
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/smb/server/mgmt/user_session.c b/fs/smb/server/mgmt/user_session.c
index 0ca788009c93..450a9f8ca7c7 100644
--- a/fs/smb/server/mgmt/user_session.c
+++ b/fs/smb/server/mgmt/user_session.c
@@ -59,10 +59,12 @@ static void ksmbd_session_rpc_clear_list(struct ksmbd_session *sess)
 	struct ksmbd_session_rpc *entry;
 	long index;
 
+	down_write(&sess->rpc_lock);
 	xa_for_each(&sess->rpc_handle_list, index, entry) {
 		xa_erase(&sess->rpc_handle_list, index);
 		__session_rpc_close(sess, entry);
 	}
+	up_write(&sess->rpc_lock);
 
 	xa_destroy(&sess->rpc_handle_list);
 }
@@ -92,7 +94,7 @@ int ksmbd_session_rpc_open(struct ksmbd_session *sess, char *rpc_name)
 {
 	struct ksmbd_session_rpc *entry, *old;
 	struct ksmbd_rpc_command *resp;
-	int method;
+	int method, id;
 
 	method = __rpc_method(rpc_name);
 	if (!method)
@@ -102,26 +104,29 @@ int ksmbd_session_rpc_open(struct ksmbd_session *sess, char *rpc_name)
 	if (!entry)
 		return -ENOMEM;
 
+	down_read(&sess->rpc_lock);
 	entry->method = method;
-	entry->id = ksmbd_ipc_id_alloc();
-	if (entry->id < 0)
+	entry->id = id = ksmbd_ipc_id_alloc();
+	if (id < 0)
 		goto free_entry;
-	old = xa_store(&sess->rpc_handle_list, entry->id, entry, GFP_KERNEL);
+	old = xa_store(&sess->rpc_handle_list, id, entry, GFP_KERNEL);
 	if (xa_is_err(old))
 		goto free_id;
 
-	resp = ksmbd_rpc_open(sess, entry->id);
+	resp = ksmbd_rpc_open(sess, id);
 	if (!resp)
 		goto erase_xa;
 
+	up_read(&sess->rpc_lock);
 	kvfree(resp);
-	return entry->id;
+	return id;
 erase_xa:
 	xa_erase(&sess->rpc_handle_list, entry->id);
 free_id:
 	ksmbd_rpc_id_free(entry->id);
 free_entry:
 	kfree(entry);
+	up_read(&sess->rpc_lock);
 	return -EINVAL;
 }
 
@@ -129,9 +134,11 @@ void ksmbd_session_rpc_close(struct ksmbd_session *sess, int id)
 {
 	struct ksmbd_session_rpc *entry;
 
+	down_write(&sess->rpc_lock);
 	entry = xa_erase(&sess->rpc_handle_list, id);
 	if (entry)
 		__session_rpc_close(sess, entry);
+	up_write(&sess->rpc_lock);
 }
 
 int ksmbd_session_rpc_method(struct ksmbd_session *sess, int id)
@@ -438,6 +445,7 @@ static struct ksmbd_session *__session_create(int protocol)
 	sess->sequence_number = 1;
 	rwlock_init(&sess->tree_conns_lock);
 	atomic_set(&sess->refcnt, 2);
+	init_rwsem(&sess->rpc_lock);
 
 	ret = __init_smb2_session(sess);
 	if (ret)
diff --git a/fs/smb/server/mgmt/user_session.h b/fs/smb/server/mgmt/user_session.h
index f21348381d59..c5749d6ec715 100644
--- a/fs/smb/server/mgmt/user_session.h
+++ b/fs/smb/server/mgmt/user_session.h
@@ -63,6 +63,7 @@ struct ksmbd_session {
 	rwlock_t			tree_conns_lock;
 
 	atomic_t			refcnt;
+	struct rw_semaphore		rpc_lock;
 };
 
 static inline int test_session_flag(struct ksmbd_session *sess, int bit)
-- 
2.34.1