[PATCH 5.15 077/530] ksmbd: Fix user namespace mapping

[Greg Kroah-Hartman]

From: Mickaël Salaün <mic@xxxxxxxxxxx>

commit 7c88c1e0ab1704bacb751341ee6431c3be34b834 upstream.

A kernel daemon should not rely on the current thread, which is unknown
and might be malicious.  Before this security fix,
ksmbd_override_fsids() didn't correctly override FS UID/GID which means
that arbitrary user space threads could trick the kernel to impersonate
arbitrary users or groups for file system access checks, leading to
file system access bypass.

This was found while investigating truncate support for Landlock:
https://lore.kernel.org/r/CAKYAXd8fpMJ7guizOjHgxEyyjoUwPsx3jLOPZP=wPYcbhkVXqA@xxxxxxxxxxxxxx

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: Hyunchul Lee <hyc.lee@xxxxxxxxx>
Cc: Steve French <smfrench@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220929100447.108468-1-mic@xxxxxxxxxxx
Acked-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
Acked-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/ksmbd/smb_common.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/ksmbd/smb_common.c
+++ b/fs/ksmbd/smb_common.c
@@ -4,6 +4,8 @@
  *   Copyright (C) 2018 Namjae Jeon <linkinjeon@xxxxxxxxxx>
  */
 
+#include <linux/user_namespace.h>
+
 #include "smb_common.h"
 #include "server.h"
 #include "misc.h"
@@ -624,8 +626,8 @@ int ksmbd_override_fsids(struct ksmbd_wo
 	if (!cred)
 		return -ENOMEM;
 
-	cred->fsuid = make_kuid(current_user_ns(), uid);
-	cred->fsgid = make_kgid(current_user_ns(), gid);
+	cred->fsuid = make_kuid(&init_user_ns, uid);
+	cred->fsgid = make_kgid(&init_user_ns, gid);
 
 	gi = groups_alloc(0);
 	if (!gi) {