FAILED: patch "[PATCH] smb: client: fix early procfs exposure race" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 7b1afb631395c958993cda4631002258ef4151ea
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110226-gigantic-arson-32db@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 7b1afb631395c958993cda4631002258ef4151ea Mon Sep 17 00:00:00 2001
From: Fredric Cover <[email protected]>
Date: Thu, 22 Oct 2026 21:55:06 +0000
Subject: [PATCH] smb: client: fix early procfs exposure race

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.

index 576155caf888..bf199a5ca084 100644
@@ -2019,7 +2019,6 @@ init_cifs(void)
 	if (rc)
 		return rc;
 
-	cifs_proc_init();
 	INIT_LIST_HEAD(&cifs_tcp_ses_list);
 /*
  *  Initialize Global counters

@@ -2068,10 +2067,8 @@ 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)

@@ -2162,19 +2159,22 @@ 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

@@ -2210,8 +2210,6 @@ init_cifs(void)
 	destroy_workqueue(decrypt_wq);
 out_destroy_cifsiod_wq:
 	destroy_workqueue(cifsiod_wq);
-out_clean_proc:
-	cifs_proc_clean();
 	return rc;
 }
 

@@ -2221,6 +2219,7 @@ 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

@@ -2243,7 +2242,6 @@ exit_cifs(void)
 	destroy_workqueue(serverclose_wq);
 	destroy_workqueue(cfid_put_wq);
 	destroy_workqueue(cifsiod_wq);
-	cifs_proc_clean();
 }
 
 MODULE_AUTHOR("Steve French");

From: Fredric Cover <[email protected]>

[ 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.

---
 fs/smb/client/cifsfs.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

index 23ec5c3666d3d..3da0fc08ffd94 100644
@@ -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