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ksmbd: Fix user namespace mapping

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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@mail.gmail.com

Fixes: e2f34481b2 ("cifsd: add server-side procedures for SMB3")
Cc: Hyunchul Lee <hyc.lee@gmail.com>
Cc: Steve French <smfrench@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220929100447.108468-1-mic@digikod.net
Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Mickaël Salaün 2022-09-29 12:04:47 +02:00 committed by Steve French
parent 5876e99611
commit 7c88c1e0ab
1 changed files with 4 additions and 2 deletions
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6
fs/ksmbd/smb_common.c
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@ -4,6 +4,8 @@
* Copyright (C) 2018 Namjae Jeon <linkinjeon@kernel.org> * Copyright (C) 2018 Namjae Jeon <linkinjeon@kernel.org>
*/ */
#include <linux/user_namespace.h>
#include "smb_common.h" #include "smb_common.h"
#include "server.h" #include "server.h"
#include "misc.h" #include "misc.h"
@ -625,8 +627,8 @@ int ksmbd_override_fsids(struct ksmbd_work *work)
if (!cred) if (!cred)
return -ENOMEM; return -ENOMEM;
cred->fsuid = make_kuid(current_user_ns(), uid); cred->fsuid = make_kuid(&init_user_ns, uid);
cred->fsgid = make_kgid(current_user_ns(), gid); cred->fsgid = make_kgid(&init_user_ns, gid);
gi = groups_alloc(0); gi = groups_alloc(0);
if (!gi) { if (!gi) {