[PATCH] smb/server: fix use-after-free in ksmbd_conn_transport_destroy()

[ChenXiaoSong <chenxiaosong@chenxiaosong.com>]

From: ChenXiaoSong <chenxiaosong@kylinos.cn>

Reproducer (Link[1]):

  1. Build kernel with CONFIG_KASAN=y
  2. server: systemctl start ksmbd
  3. client: mount -t cifs //localhost/export /mnt
  4. client: umount /mnt
  5. server: modprobe -r ksmbd

The error message is as follows:

  ==================================================================
  BUG: KASAN: slab-use-after-free in proc_remove+0x3e/0x80
  Read of size 8 at addr ffff88810654e098 by task modprobe/785
  ...
  Call Trace:
   <TASK>
   __dump_stack+0x19/0x30
   dump_stack_lvl+0x49/0x60
   print_address_description+0x7b/0x200
   print_report+0x5b/0x70
   kasan_report+0xed/0x130
   __asan_report_load8_noabort+0x18/0x20
   proc_remove+0x3e/0x80
   ksmbd_conn_transport_destroy+0x2b/0x320 [ksmbd]
   cleanup_module+0x33/0xe00 [ksmbd]
   __se_sys_delete_module+0x276/0x400
   __x64_sys_delete_module+0x5f/0x70
   x64_sys_call+0x2675/0x3030
   do_syscall_64+0xf0/0x3b0
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
  RIP: 0033:0x7f5b56d2b02b
  ...
   </TASK>

  Allocated by task 159:
   kasan_save_track+0x2f/0x70
   kasan_save_alloc_info+0x40/0x50
   __kasan_slab_alloc+0x52/0x70
   kmem_cache_alloc_noprof+0x168/0x3e0
   __proc_create+0x20b/0x710
   proc_create_single_data+0x78/0x150
   ksmbd_proc_create+0x24/0x30 [ksmbd]
   ksmbd_conn_transport_init+0x4f/0x80 [ksmbd]
   server_ctrl_handle_work+0x64/0x2c0 [ksmbd]
   process_scheduled_works+0x788/0xec0
   worker_thread+0x894/0xc10
   kthread+0x2e5/0x3c0
   ret_from_fork+0x168/0x4f0
   ret_from_fork_asm+0x1a/0x30

  Freed by task 785:
   kasan_save_track+0x2f/0x70
   kasan_save_free_info+0x4a/0x60
   __kasan_slab_free+0x47/0x70
   kmem_cache_free+0x122/0x410
   pde_put+0xfd/0x160
   remove_proc_subtree+0x365/0x540
   proc_remove+0x6a/0x80
   ksmbd_proc_cleanup+0x1f/0x60 [ksmbd]
   cleanup_module+0x18/0xe00 [ksmbd]
   __se_sys_delete_module+0x276/0x400
   __x64_sys_delete_module+0x5f/0x70
   x64_sys_call+0x2675/0x3030
   do_syscall_64+0xf0/0x3b0
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
  ==================================================================

Reported-by: Kyenghwan Hwang <obnred@gmail.com>
Link[1]: https://lore.kernel.org/linux-cifs/8ea028f5-90f4-4d21-b1ac-a343f0f04d88@chenxiaosong.com/
Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
---
 fs/smb/server/server.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/smb/server/server.c b/fs/smb/server/server.c
index 0ccd123ba418..d619d1f22601 100644
--- a/fs/smb/server/server.c
+++ b/fs/smb/server/server.c
@@ -596,11 +596,16 @@ static int ksmbd_server_shutdown(void)
 {
 	WRITE_ONCE(server_conf.state, SERVER_STATE_SHUTTING_DOWN);
 
-	ksmbd_proc_cleanup();
 	class_unregister(&ksmbd_control_class);
 	ksmbd_workqueue_destroy();
 	ksmbd_ipc_release();
 	ksmbd_conn_transport_destroy();
+	/*
+	 * ksmbd_conn_transport_destroy() calls delete_proc_clients() and destroys
+	 * sessions. ksmbd_session_destroy() removes each session's proc entry.
+	 * Keep the procfs tree alive until these entries have been removed.
+	 */
+	ksmbd_proc_cleanup();
 	ksmbd_crypto_destroy();
 	ksmbd_free_global_file_table();
 	destroy_lease_table(NULL);
-- 
2.54.0