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[PATCH 2/9] security: Make capabilities relative to the user namespace. [message #41744 is a reply to message #41743] Thu, 17 February 2011 15:03 Go to previous messageGo to previous message
serge is currently offline  serge
Messages: 72
Registered: January 2007
Member
- Introduce ns_capable to test for a capability in a non-default
user namespace.
- Teach cap_capable to handle capabilities in a non-default
user namespace.

The motivation is to get to the unprivileged creation of new
namespaces. It looks like this gets us 90% of the way there, with
only potential uid confusion issues left.

I still need to handle getting all caps after creation but otherwise I
think I have a good starter patch that achieves all of your goals.

Changelog:
11/05/2010: [serge] add apparmor
12/14/2010: [serge] fix capabilities to created user namespaces
Without this, if user serge creates a user_ns, he won't have
capabilities to the user_ns he created. THis is because we
were first checking whether his effective caps had the caps
he needed and returning -EPERM if not, and THEN checking whether
he was the creator. Reverse those checks.
12/16/2010: [serge] security_real_capable needs ns argument in !security case
01/11/2011: [serge] add task_ns_capable helper
01/11/2011: [serge] add nsown_capable() helper per Bastian Blank suggestion
02/16/2011: [serge] fix a logic bug: the root user is always creator of
init_user_ns, but should not always have capabilities to
it! Fix the check in cap_capable().

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
---
include/linux/capability.h | 10 ++++++++--
include/linux/security.h | 25 ++++++++++++++-----------
kernel/capability.c | 32 ++++++++++++++++++++++++++++++--
security/apparmor/lsm.c | 5 +++--
security/commoncap.c | 40 +++++++++++++++++++++++++++++++++-------
security/security.c | 16 ++++++++++------
security/selinux/hooks.c | 14 +++++++++-----
7 files changed, 107 insertions(+), 35 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index fb16a36..cb3d2d9 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -544,7 +544,7 @@ extern const kernel_cap_t __cap_init_eff_set;
*
* Note that this does not set PF_SUPERPRIV on the task.
*/
-#define has_capability(t, cap) (security_real_capable((t), (cap)) == 0)
+#define has_capability(t, cap) (security_real_capable((t), &init_user_ns, (cap)) == 0)

/**
* has_capability_noaudit - Determine if a task has a superior capability available (unaudited)
@@ -558,9 +558,15 @@ extern const kernel_cap_t __cap_init_eff_set;
* Note that this does not set PF_SUPERPRIV on the task.
*/
#define has_capability_noaudit(t, cap) \
- (security_real_capable_noaudit((t), (cap)) == 0)
+ (security_real_capable_noaudit((t), &init_user_ns, (cap)) == 0)

+struct user_namespace;
+extern struct user_namespace init_user_ns;
extern int capable(int cap);
+extern int ns_capable(struct user_namespace *ns, int cap);
+extern int task_ns_capable(struct task_struct *t, int cap);
+
+#define nsown_capable(cap) (ns_capable(current_user_ns(), (cap)))

/* audit system wants to get cap info from files as well */
struct dentry;
diff --git a/include/linux/security.h b/include/linux/security.h
index b2b7f97..6bbee08 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -46,13 +46,14 @@

struct ctl_table;
struct audit_krule;
+struct user_namespace;

/*
* These functions are in security/capability.c and are used
* as the default capabilities functions
*/
extern int cap_capable(struct task_struct *tsk, const struct cred *cred,
- int cap, int audit);
+ struct user_namespace *ns, int cap, int audit);
extern int cap_settime(struct timespec *ts, struct timezone *tz);
extern int cap_ptrace_access_check(struct task_struct *child, unsigned int mode);
extern int cap_ptrace_traceme(struct task_struct *parent);
@@ -1254,6 +1255,7 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
* credentials.
* @tsk contains the task_struct for the process.
* @cred contains the credentials to use.
+ * @ns contains the user namespace we want the capability in
* @cap contains the capability <include/linux/capability.h>.
* @audit: Whether to write an audit message or not
* Return 0 if the capability is granted for @tsk.
@@ -1382,7 +1384,7 @@ struct security_operations {
const kernel_cap_t *inheritable,
const kernel_cap_t *permitted);
int (*capable) (struct task_struct *tsk, const struct cred *cred,
- int cap, int audit);
+ struct user_namespace *ns, int cap, int audit);
int (*sysctl) (struct ctl_table *table, int op);
int (*quotactl) (int cmds, int type, int id, struct super_block *sb);
int (*quota_on) (struct dentry *dentry);
@@ -1662,9 +1664,9 @@ int security_capset(struct cred *new, const struct cred *old,
const kernel_cap_t *effective,
const kernel_cap_t *inheritable,
const kernel_cap_t *permitted);
-int security_capable(const struct cred *cred, int cap);
-int security_real_capable(struct task_struct *tsk, int cap);
-int security_real_capable_noaudit(struct task_struct *tsk, int cap);
+int security_capable(struct user_namespace *ns, const struct cred *cred, int cap);
+int security_real_capable(struct task_struct *tsk, struct user_namespace *ns, int cap);
+int security_real_capable_noaudit(struct task_struct *tsk, struct user_namespace *ns, int cap);
int security_sysctl(struct ctl_table *table, int op);
int security_quotactl(int cmds, int type, int id, struct super_block *sb);
int security_quota_on(struct dentry *dentry);
@@ -1856,28 +1858,29 @@ static inline int security_capset(struct cred *new,
return cap_capset(new, old, effective, inheritable, permitted);
}

-static inline int security_capable(const struct cred *cred, int cap)
+static inline int security_capable(struct user_namespace *ns,
+ const struct cred *cred, int cap)
{
- return cap_capable(current, cred, cap, SECURITY_CAP_AUDIT);
+ return cap_capable(current, cred, ns, cap, SECURITY_CAP_AUDIT);
}

-static inline int security_real_capable(struct task_struct *tsk, int cap)
+static inline int security_real_capable(struct task_struct *tsk, struct user_namespace *ns, int cap)
{
int ret;

rcu_read_lock();
- ret = cap_capable(tsk, __task_cred(tsk), cap, SECURITY_CAP_AUDIT);
+ ret = cap_capable(tsk, __task_cred(tsk), ns, cap, SECURITY_CAP_AUDIT);
rcu_read_unlock();
return ret;
}

static inline
-int security_real_capable_noaudit(struct task_struct *tsk, int cap)
+int security_real_capable_noaudit(struct task_struct *tsk, struct user_namespace *ns, int cap)
{
int ret;

rcu_read_lock();
- ret = cap_capable(tsk, __task_cred(tsk), cap,
+ ret = cap_capable(tsk, __task_cred(tsk), ns, cap,
SECURITY_CAP_NOAUDIT);
rcu_read_unlock();
return ret;
diff --git a/kernel/capability.c b/kernel/capability.c
index 9e9385f..916658c 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -14,6 +14,7 @@
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
#include <asm/uaccess.h>

/*
@@ -301,15 +302,42 @@ error:
*/
int capable(int cap)
{
+ return ns_capable(&init_user_ns, cap);
+}
+EXPORT_SYMBOL(capable);
+
+/**
+ * ns_capable - Determine if the current task has a superior capability in effect
+ * @ns: The usernamespace we want the capability in
+ * @cap: The capability to be tested for
+ *
+ * Return true if the current task has the given superior capability currently
+ * available for use, false if not.
+ *
+ * This sets PF_SUPERPRIV on the task if the capability is available on the
+ * assumption that it's about to be used.
+ */
+int ns_capable(struct user_namespace *ns, int cap)
+{
if (unlikely(!cap_valid(cap))) {
printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
BUG();
}

- if (security_capable(current_cred(), cap) == 0) {
+ if (security_capable(ns, current_cred(), cap) == 0) {
current->flags |= PF_SUPERPRIV;
return 1;
}
return 0;
}
-EXPORT_SYMBOL(capable);
+EXPORT_SYMBOL(ns_capable);
+
+/*
+ * does current have capability 'cap' to the user namespace of task
+ * 't'. Return true if it does, false otherwise.
+ */
+int task_ns_capable(struct task_struct *t, int cap)
+{
+ return ns_capable(task_cred_xxx(t, user)->user_ns, cap);
+}
+EXPORT_SYMBOL(task_ns_capable);
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index b7106f1..b37c2cd 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -22,6 +22,7 @@
#include <linux/ctype.h>
#include <linux/sysctl.h>
#include <linux/audit.h>
+#include <linux/user_namespace.h>
#include <net/sock.h>

#include "include/apparmor.h"
@@ -136,11 +137,11 @@ static int apparmor_capget(struct task_struct *target, kernel_cap_t *effective,
}

static int apparmor_capable(struct task_struct *task, const struct cred *cred,
- int cap, int audit)
+ struct user_namespace *ns, int cap, int audit)
{
struct aa_profile *profile;
/* cap_capable returns 0 on success, else -EPERM */
- int error = cap_capable(task, cred, cap, audit);
+ int error = cap_capable(task, cred, ns, cap, audit);
if (!error) {
profile = aa_cred_profile(cred);
if (!unconfined(profile))
diff --git a/security/commoncap.c b/security/commoncap.c
index 64c2ed9..51fa9ec 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -27,6 +27,7 @@
#include <linux/sched.h>
#include <linux/prctl.h>
#include <linux/securebits.h>
+#include <linux/user_namespace.h>

/*
* If a non-root user executes a setuid-root binary in
@@ -68,6 +69,7 @@ EXPORT_SYMBOL(cap_netlink_recv);
* cap_capable - Determine whether a task has a particular effective capability
* @tsk: The task to query
* @cred: The credentials to use
+ * @ns: The user namespace in which we need the capability
* @cap: The capability to check for
* @audit: Whether to write ...

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