Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751694AbeACH1G (ORCPT + 1 other); Wed, 3 Jan 2018 02:27:06 -0500 Received: from mail-io0-f194.google.com ([209.85.223.194]:43671 "EHLO mail-io0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751605AbeACH1C (ORCPT ); Wed, 3 Jan 2018 02:27:02 -0500 X-Google-Smtp-Source: ACJfBos3N3Qzvln/jhsC9V4A92mTys6nVgT5RC1M/NW6PalYvQdY6KuysqHBqE4Vo3qWFbeGiE6L3A== From: Mahesh Bandewar To: LKML , James Morris Cc: Netdev , Kernel-hardening , Linux API , Linux Security , Serge Hallyn , Michael Kerrisk , Kees Cook , "Eric W . Biederman" , Eric Dumazet , David Miller , Mahesh Bandewar , Mahesh Bandewar Subject: [PATCHv4 2/2] userns: control capabilities of some user namespaces Date: Tue, 2 Jan 2018 23:26:57 -0800 Message-Id: <20180103072657.161985-1-mahesh@bandewar.net> X-Mailer: git-send-email 2.15.1.620.gb9897f4670-goog Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: From: Mahesh Bandewar With this new notion of "controlled" user-namespaces, the controlled user-namespaces are marked at the time of their creation while the capabilities of processes that belong to them are controlled using the global mask. Init-user-ns is always uncontrolled and a process that has SYS_ADMIN that belongs to uncontrolled user-ns can create another (child) user- namespace that is uncontrolled. Any other process (that either does not have SYS_ADMIN or belongs to a controlled user-ns) can only create a user-ns that is controlled. global-capability-whitelist (controlled_userns_caps_whitelist) is used at the capability check-time and keeps the semantics for the processes that belong to uncontrolled user-ns as it is. Processes that belong to controlled user-ns however are subjected to different checks- (a) if the capability in question is controlled and process belongs to controlled user-ns, then it's always denied. (b) if the capability in question is NOT controlled then fall back to the traditional check. Acked-by: Serge Hallyn Signed-off-by: Mahesh Bandewar --- v4: Rebase v3: Rebase v2: Don't recalculate user-ns flags for every setns() call. v1: Initial submission. include/linux/capability.h | 4 ++++ include/linux/user_namespace.h | 25 +++++++++++++++++++++++++ kernel/capability.c | 5 +++++ kernel/user_namespace.c | 4 ++++ security/commoncap.c | 8 ++++++++ 5 files changed, 46 insertions(+) diff --git a/include/linux/capability.h b/include/linux/capability.h index 7d79a4689625..383f31f066f0 100644 --- a/include/linux/capability.h +++ b/include/linux/capability.h @@ -251,6 +251,10 @@ extern bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns); extern int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps); int proc_douserns_caps_whitelist(struct ctl_table *table, int write, void __user *buff, size_t *lenp, loff_t *ppos); +/* Controlled capability is capability that is missing from the capability-mask + * controlled_userns_caps_whitelist controlled via sysctl. + */ +bool is_capability_controlled(int cap); extern int cap_convert_nscap(struct dentry *dentry, void **ivalue, size_t size); diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index d6b74b91096b..a5c48684b317 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -32,6 +32,7 @@ struct uid_gid_map { /* 64 bytes -- 1 cache line */ }; #define USERNS_SETGROUPS_ALLOWED 1UL +#define USERNS_CONTROLLED 2UL #define USERNS_INIT_FLAGS USERNS_SETGROUPS_ALLOWED @@ -112,6 +113,21 @@ static inline void put_user_ns(struct user_namespace *ns) __put_user_ns(ns); } +/* Controlled user-ns is the one that is created by a process that does not + * have CAP_SYS_ADMIN (or descended from such an user-ns). + * For more details please see the sysctl description of + * controlled_userns_caps_whitelist. + */ +static inline bool is_user_ns_controlled(const struct user_namespace *ns) +{ + return ns->flags & USERNS_CONTROLLED; +} + +static inline void mark_user_ns_controlled(struct user_namespace *ns) +{ + ns->flags |= USERNS_CONTROLLED; +} + struct seq_operations; extern const struct seq_operations proc_uid_seq_operations; extern const struct seq_operations proc_gid_seq_operations; @@ -170,6 +186,15 @@ static inline struct ns_common *ns_get_owner(struct ns_common *ns) { return ERR_PTR(-EPERM); } + +static inline bool is_user_ns_controlled(const struct user_namespace *ns) +{ + return false; +} + +static inline void mark_user_ns_controlled(struct user_namespace *ns) +{ +} #endif #endif /* _LINUX_USER_H */ diff --git a/kernel/capability.c b/kernel/capability.c index 4a859b7d4902..bffe249922de 100644 --- a/kernel/capability.c +++ b/kernel/capability.c @@ -511,6 +511,11 @@ bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns) } /* Controlled-userns capabilities routines */ +bool is_capability_controlled(int cap) +{ + return !cap_raised(controlled_userns_caps_whitelist, cap); +} + #ifdef CONFIG_SYSCTL int proc_douserns_caps_whitelist(struct ctl_table *table, int write, void __user *buff, size_t *lenp, loff_t *ppos) diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 246d4d4ce5c7..ca0556d466b6 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -141,6 +141,10 @@ int create_user_ns(struct cred *new) goto fail_keyring; set_cred_user_ns(new, ns); + if (!ns_capable(parent_ns, CAP_SYS_ADMIN) || + is_user_ns_controlled(parent_ns)) + mark_user_ns_controlled(ns); + return 0; fail_keyring: #ifdef CONFIG_PERSISTENT_KEYRINGS diff --git a/security/commoncap.c b/security/commoncap.c index 4f8e09340956..5454e9c03ee8 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -73,6 +73,14 @@ int cap_capable(const struct cred *cred, struct user_namespace *targ_ns, { struct user_namespace *ns = targ_ns; + /* If the capability is controlled and user-ns that process + * belongs-to is 'controlled' then return EPERM and no need + * to check the user-ns hierarchy. + */ + if (is_user_ns_controlled(cred->user_ns) && + is_capability_controlled(cap)) + return -EPERM; + /* See if cred has the capability in the target user namespace * by examining the target user namespace and all of the target * user namespace's parents. -- 2.15.1.620.gb9897f4670-goog