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Message-Id: <20170921215654.11280-1-mahesh@bandewar.net>
Date: Thu, 21 Sep 2017 14:56:54 -0700
From: Mahesh Bandewar <mahesh@...dewar.net>
To: LKML <linux-kernel@...r.kernel.org>,
Netdev <netdev@...r.kernel.org>
Cc: Kees Cook <keescook@...omium.org>, Serge Hallyn <serge@...lyn.com>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Eric Dumazet <edumazet@...gle.com>,
David Miller <davem@...emloft.net>,
Mahesh Bandewar <mahesh@...dewar.net>,
Mahesh Bandewar <maheshb@...gle.com>
Subject: [RFC PATCH 2/2] userns: control capabilities of some user namespaces
From: Mahesh Bandewar <maheshb@...gle.com>
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.
Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
---
include/linux/capability.h | 1 +
include/linux/user_namespace.h | 20 ++++++++++++++++++++
kernel/capability.c | 5 +++++
kernel/user_namespace.c | 3 +++
security/commoncap.c | 8 ++++++++
5 files changed, 37 insertions(+)
diff --git a/include/linux/capability.h b/include/linux/capability.h
index 6c0b9677c03f..b8c6cac18658 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -250,6 +250,7 @@ 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);
+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 c18e01252346..e890fe81b47e 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -22,6 +22,7 @@ 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
@@ -102,6 +103,16 @@ static inline void put_user_ns(struct user_namespace *ns)
__put_user_ns(ns);
}
+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;
@@ -160,6 +171,15 @@ 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 62dbe3350c1b..40a38cc4ff43 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -510,6 +510,11 @@ 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 c490f1e4313b..f393ea5108f0 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -53,6 +53,9 @@ static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns)
cred->cap_effective = CAP_FULL_SET;
cred->cap_ambient = CAP_EMPTY_SET;
cred->cap_bset = CAP_FULL_SET;
+ if (!ns_capable(user_ns->parent, CAP_SYS_ADMIN) ||
+ is_user_ns_controlled(user_ns->parent))
+ mark_user_ns_controlled(user_ns);
#ifdef CONFIG_KEYS
key_put(cred->request_key_auth);
cred->request_key_auth = NULL;
diff --git a/security/commoncap.c b/security/commoncap.c
index 6bf72b175b49..26f41602da10 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.
--
2.14.1.821.g8fa685d3b7-goog
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