[PATCH 6.18.y] smb: client: fix early procfs exposure race

[Sasha Levin <sashal@kernel.org>]

From: Fredric Cover <fredric.cover.lkernel@gmail.com>

[ Upstream commit 7b1afb631395c958993cda4631002258ef4151ea ]

Currently, init_cifs() calls cifs_proc_init() near the beginning of
the function, before INIT_LIST_HEAD, leading to a momentarily
uninitialized, but exposed, procfs. If a userspace process reads this
empty procfs, iterating over a zeroed list_head leads to a NULL
pointer dereference and a kernel oops/panic.

For example, if a delay is added between cifs_proc_init() and
INIT_LIST_HEAD, and a userspace process is polling
/proc/fs/cifs/DebugData, the following oops occurs:

BUG: kernel NULL pointer dereference, address: 0000000000000608
Oops: Oops: 0000 [#1] SMP PTI
CPU: 0 UID: 0 PID: 3477 Comm: cat Not tainted
7.3.0-02212-g4df4d2a577db-dirty #6 PREEMPT(lazy)
RIP: 0010:cifs_debug_data_proc_show+0x103/0xd80 [cifs]
Call Trace:
<TASK>
 ? seq_read_iter+0x86/0x400
 ? seq_read_iter+0x86/0x400
 seq_read_iter+0x183/0x400
 proc_reg_read_iter+0x62/0x90
 copy_splice_read+0x215/0x310
 splice_file_to_pipe+0xec/0x1c0
 do_splice+0x4b8/0x780
 __se_sys_splice+0x18f/0x250
 do_syscall_64+0x109/0x330
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>

Fix this by moving cifs_proc_init() down in init_cifs(), ensuring it runs
only after all internal lists, locks, counters, and workqueues are fully
ready, but before registering the filesystem. Update the error cleanup
ladder and exit_cifs() to maintain proper LIFO order.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Fredric Cover <fredric.cover.lkernel@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
[ sashal: Adjusted init_cifs() context because smb1_init_maperror() and smb2_init_maperror() are absent. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/client/cifsfs.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 23ec5c3666d3d..3da0fc08ffd94 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -1972,7 +1972,6 @@ static int __init
 init_cifs(void)
 {
 	int rc = 0;
-	cifs_proc_init();
 	INIT_LIST_HEAD(&cifs_tcp_ses_list);
 /*
  *  Initialize Global counters
@@ -2021,10 +2020,8 @@ init_cifs(void)
 	cifsiod_wq = alloc_workqueue("cifsiod",
 				     WQ_FREEZABLE | WQ_MEM_RECLAIM | WQ_PERCPU,
 				     0);
-	if (!cifsiod_wq) {
-		rc = -ENOMEM;
-		goto out_clean_proc;
-	}
+	if (!cifsiod_wq)
+		return -ENOMEM;
 
 	/*
 	 * Consider in future setting limit!=0 maybe to min(num_of_cores - 1, 3)
@@ -2115,19 +2112,22 @@ init_cifs(void)
 	if (rc)
 		goto out_cifs_swn_init;
 
+	cifs_proc_init();
+
 	rc = register_filesystem(&cifs_fs_type);
 	if (rc)
-		goto out_init_cifs_idmap;
+		goto out_clean_proc;
 
 	rc = register_filesystem(&smb3_fs_type);
 	if (rc) {
 		unregister_filesystem(&cifs_fs_type);
-		goto out_init_cifs_idmap;
+		goto out_clean_proc;
 	}
 
 	return 0;
 
-out_init_cifs_idmap:
+out_clean_proc:
+	cifs_proc_clean();
 	exit_cifs_idmap();
 out_cifs_swn_init:
 #ifdef CONFIG_CIFS_SWN_UPCALL
@@ -2163,8 +2163,6 @@ init_cifs(void)
 	destroy_workqueue(decrypt_wq);
 out_destroy_cifsiod_wq:
 	destroy_workqueue(cifsiod_wq);
-out_clean_proc:
-	cifs_proc_clean();
 	return rc;
 }
 
@@ -2174,6 +2172,7 @@ exit_cifs(void)
 	cifs_dbg(NOISY, "exit_smb3\n");
 	unregister_filesystem(&cifs_fs_type);
 	unregister_filesystem(&smb3_fs_type);
+	cifs_proc_clean();
 	cifs_release_automount_timer();
 	exit_cifs_idmap();
 #ifdef CONFIG_CIFS_SWN_UPCALL
@@ -2196,7 +2195,6 @@ exit_cifs(void)
 	destroy_workqueue(serverclose_wq);
 	destroy_workqueue(cfid_put_wq);
 	destroy_workqueue(cifsiod_wq);
-	cifs_proc_clean();
 }
 
 MODULE_AUTHOR("Steve French");
-- 
2.53.0