[PATCH 6.6 50/72] ksmbd: Fix race condition in RPC handle list access

Greg Kroah-Hartman
2026-02-04T15:21:43Z

From: Yunseong Kim <ysk@kzalloc.com>

[ Upstream commit 305853cce379407090a73b38c5de5ba748893aee ]

The 'sess->rpc_handle_list' XArray manages RPC handles within a ksmbd
session. Access to this list is intended to be protected by
'sess->rpc_lock' (an rw_semaphore). However, the locking implementation was
flawed, leading to potential race conditions.

In ksmbd_session_rpc_open(), the code incorrectly acquired only a read lock
before calling xa_store() and xa_erase(). Since these operations modify
the XArray structure, a write lock is required to ensure exclusive access
and prevent data corruption from concurrent modifications.

Furthermore, ksmbd_session_rpc_method() accessed the list using xa_load()
without holding any lock at all. This could lead to reading inconsistent
data or a potential use-after-free if an entry is concurrently removed and
the pointer is dereferenced.

Fix these issues by:
1. Using down_write() and up_write() in ksmbd_session_rpc_open()
to ensure exclusive access during XArray modification, and ensuring
the lock is correctly released on error paths.
2. Adding down_read() and up_read() in ksmbd_session_rpc_method()
to safely protect the lookup.

Fixes: a1f46c99d9ea ("ksmbd: fix use-after-free in ksmbd_session_rpc_open")
Fixes: b685757c7b08 ("ksmbd: Implements sess->rpc_handle_list as xarray")
Cc: stable@vger.kernel.org
Signed-off-by: Yunseong Kim <ysk@kzalloc.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
[ Minor conflict resolved. ]
Signed-off-by: Li hongliang <1468888505@139.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/smb/server/mgmt/user_session.c | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)

--- a/fs/smb/server/mgmt/user_session.c
+++ b/fs/smb/server/mgmt/user_session.c
@@ -104,29 +104,32 @@ int ksmbd_session_rpc_open(struct ksmbd_
if (!entry)
return -ENOMEM;

- down_read(&sess->rpc_lock);
entry->method = method;
entry->id = id = ksmbd_ipc_id_alloc();
if (id < 0)
goto free_entry;
+
+ down_write(&sess->rpc_lock);
old = xa_store(&sess->rpc_handle_list, id, entry, GFP_KERNEL);
- if (xa_is_err(old))
+ if (xa_is_err(old)) {
+ up_write(&sess->rpc_lock);
goto free_id;
+ }

resp = ksmbd_rpc_open(sess, id);
- if (!resp)
- goto erase_xa;
+ if (!resp) {
+ xa_erase(&sess->rpc_handle_list, entry->id);
+ up_write(&sess->rpc_lock);
+ goto free_id;
+ }

- up_read(&sess->rpc_lock);
+ up_write(&sess->rpc_lock);
kvfree(resp);
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;
}

@@ -144,9 +147,14 @@ void ksmbd_session_rpc_close(struct ksmb
int ksmbd_session_rpc_method(struct ksmbd_session *sess, int id)
{
struct ksmbd_session_rpc *entry;
+ int method;

+ down_read(&sess->rpc_lock);
entry = xa_load(&sess->rpc_handle_list, id);
- return entry ? entry->method : 0;
+ method = entry ? entry->method : 0;
+ up_read(&sess->rpc_lock);
+
+ return method;
}

void ksmbd_session_destroy(struct ksmbd_session *sess)