android_kernel_motorola_sm6225/kernel/cred.c
Serge Hallyn 18b6e0414e User namespaces: set of cleanups (v2)
The user_ns is moved from nsproxy to user_struct, so that a struct
cred by itself is sufficient to determine access (which it otherwise
would not be).  Corresponding ecryptfs fixes (by David Howells) are
here as well.

Fix refcounting.  The following rules now apply:
        1. The task pins the user struct.
        2. The user struct pins its user namespace.
        3. The user namespace pins the struct user which created it.

User namespaces are cloned during copy_creds().  Unsharing a new user_ns
is no longer possible.  (We could re-add that, but it'll cause code
duplication and doesn't seem useful if PAM doesn't need to clone user
namespaces).

When a user namespace is created, its first user (uid 0) gets empty
keyrings and a clean group_info.

This incorporates a previous patch by David Howells.  Here
is his original patch description:

>I suggest adding the attached incremental patch.  It makes the following
>changes:
>
> (1) Provides a current_user_ns() macro to wrap accesses to current's user
>     namespace.
>
> (2) Fixes eCryptFS.
>
> (3) Renames create_new_userns() to create_user_ns() to be more consistent
>     with the other associated functions and because the 'new' in the name is
>     superfluous.
>
> (4) Moves the argument and permission checks made for CLONE_NEWUSER to the
>     beginning of do_fork() so that they're done prior to making any attempts
>     at allocation.
>
> (5) Calls create_user_ns() after prepare_creds(), and gives it the new creds
>     to fill in rather than have it return the new root user.  I don't imagine
>     the new root user being used for anything other than filling in a cred
>     struct.
>
>     This also permits me to get rid of a get_uid() and a free_uid(), as the
>     reference the creds were holding on the old user_struct can just be
>     transferred to the new namespace's creator pointer.
>
> (6) Makes create_user_ns() reset the UIDs and GIDs of the creds under
>     preparation rather than doing it in copy_creds().
>
>David

>Signed-off-by: David Howells <dhowells@redhat.com>

Changelog:
	Oct 20: integrate dhowells comments
		1. leave thread_keyring alone
		2. use current_user_ns() in set_user()

Signed-off-by: Serge Hallyn <serue@us.ibm.com>
2008-11-24 18:57:41 -05:00

588 lines
14 KiB
C

/* Task credentials management - see Documentation/credentials.txt
*
* Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#include <linux/module.h>
#include <linux/cred.h>
#include <linux/sched.h>
#include <linux/key.h>
#include <linux/keyctl.h>
#include <linux/init_task.h>
#include <linux/security.h>
#include <linux/cn_proc.h>
#include "cred-internals.h"
static struct kmem_cache *cred_jar;
/*
* The common credentials for the initial task's thread group
*/
#ifdef CONFIG_KEYS
static struct thread_group_cred init_tgcred = {
.usage = ATOMIC_INIT(2),
.tgid = 0,
.lock = SPIN_LOCK_UNLOCKED,
};
#endif
/*
* The initial credentials for the initial task
*/
struct cred init_cred = {
.usage = ATOMIC_INIT(4),
.securebits = SECUREBITS_DEFAULT,
.cap_inheritable = CAP_INIT_INH_SET,
.cap_permitted = CAP_FULL_SET,
.cap_effective = CAP_INIT_EFF_SET,
.cap_bset = CAP_INIT_BSET,
.user = INIT_USER,
.group_info = &init_groups,
#ifdef CONFIG_KEYS
.tgcred = &init_tgcred,
#endif
};
/*
* Dispose of the shared task group credentials
*/
#ifdef CONFIG_KEYS
static void release_tgcred_rcu(struct rcu_head *rcu)
{
struct thread_group_cred *tgcred =
container_of(rcu, struct thread_group_cred, rcu);
BUG_ON(atomic_read(&tgcred->usage) != 0);
key_put(tgcred->session_keyring);
key_put(tgcred->process_keyring);
kfree(tgcred);
}
#endif
/*
* Release a set of thread group credentials.
*/
static void release_tgcred(struct cred *cred)
{
#ifdef CONFIG_KEYS
struct thread_group_cred *tgcred = cred->tgcred;
if (atomic_dec_and_test(&tgcred->usage))
call_rcu(&tgcred->rcu, release_tgcred_rcu);
#endif
}
/*
* The RCU callback to actually dispose of a set of credentials
*/
static void put_cred_rcu(struct rcu_head *rcu)
{
struct cred *cred = container_of(rcu, struct cred, rcu);
if (atomic_read(&cred->usage) != 0)
panic("CRED: put_cred_rcu() sees %p with usage %d\n",
cred, atomic_read(&cred->usage));
security_cred_free(cred);
key_put(cred->thread_keyring);
key_put(cred->request_key_auth);
release_tgcred(cred);
put_group_info(cred->group_info);
free_uid(cred->user);
kmem_cache_free(cred_jar, cred);
}
/**
* __put_cred - Destroy a set of credentials
* @cred: The record to release
*
* Destroy a set of credentials on which no references remain.
*/
void __put_cred(struct cred *cred)
{
BUG_ON(atomic_read(&cred->usage) != 0);
call_rcu(&cred->rcu, put_cred_rcu);
}
EXPORT_SYMBOL(__put_cred);
/**
* prepare_creds - Prepare a new set of credentials for modification
*
* Prepare a new set of task credentials for modification. A task's creds
* shouldn't generally be modified directly, therefore this function is used to
* prepare a new copy, which the caller then modifies and then commits by
* calling commit_creds().
*
* Preparation involves making a copy of the objective creds for modification.
*
* Returns a pointer to the new creds-to-be if successful, NULL otherwise.
*
* Call commit_creds() or abort_creds() to clean up.
*/
struct cred *prepare_creds(void)
{
struct task_struct *task = current;
const struct cred *old;
struct cred *new;
BUG_ON(atomic_read(&task->real_cred->usage) < 1);
new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
if (!new)
return NULL;
old = task->cred;
memcpy(new, old, sizeof(struct cred));
atomic_set(&new->usage, 1);
get_group_info(new->group_info);
get_uid(new->user);
#ifdef CONFIG_KEYS
key_get(new->thread_keyring);
key_get(new->request_key_auth);
atomic_inc(&new->tgcred->usage);
#endif
#ifdef CONFIG_SECURITY
new->security = NULL;
#endif
if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
goto error;
return new;
error:
abort_creds(new);
return NULL;
}
EXPORT_SYMBOL(prepare_creds);
/*
* Prepare credentials for current to perform an execve()
* - The caller must hold current->cred_exec_mutex
*/
struct cred *prepare_exec_creds(void)
{
struct thread_group_cred *tgcred = NULL;
struct cred *new;
#ifdef CONFIG_KEYS
tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
if (!tgcred)
return NULL;
#endif
new = prepare_creds();
if (!new) {
kfree(tgcred);
return new;
}
#ifdef CONFIG_KEYS
/* newly exec'd tasks don't get a thread keyring */
key_put(new->thread_keyring);
new->thread_keyring = NULL;
/* create a new per-thread-group creds for all this set of threads to
* share */
memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
atomic_set(&tgcred->usage, 1);
spin_lock_init(&tgcred->lock);
/* inherit the session keyring; new process keyring */
key_get(tgcred->session_keyring);
tgcred->process_keyring = NULL;
release_tgcred(new);
new->tgcred = tgcred;
#endif
return new;
}
/*
* prepare new credentials for the usermode helper dispatcher
*/
struct cred *prepare_usermodehelper_creds(void)
{
#ifdef CONFIG_KEYS
struct thread_group_cred *tgcred = NULL;
#endif
struct cred *new;
#ifdef CONFIG_KEYS
tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
if (!tgcred)
return NULL;
#endif
new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
if (!new)
return NULL;
memcpy(new, &init_cred, sizeof(struct cred));
atomic_set(&new->usage, 1);
get_group_info(new->group_info);
get_uid(new->user);
#ifdef CONFIG_KEYS
new->thread_keyring = NULL;
new->request_key_auth = NULL;
new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
atomic_set(&tgcred->usage, 1);
spin_lock_init(&tgcred->lock);
new->tgcred = tgcred;
#endif
#ifdef CONFIG_SECURITY
new->security = NULL;
#endif
if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
goto error;
BUG_ON(atomic_read(&new->usage) != 1);
return new;
error:
put_cred(new);
return NULL;
}
/*
* Copy credentials for the new process created by fork()
*
* We share if we can, but under some circumstances we have to generate a new
* set.
*
* The new process gets the current process's subjective credentials as its
* objective and subjective credentials
*/
int copy_creds(struct task_struct *p, unsigned long clone_flags)
{
#ifdef CONFIG_KEYS
struct thread_group_cred *tgcred;
#endif
struct cred *new;
int ret;
mutex_init(&p->cred_exec_mutex);
if (
#ifdef CONFIG_KEYS
!p->cred->thread_keyring &&
#endif
clone_flags & CLONE_THREAD
) {
p->real_cred = get_cred(p->cred);
get_cred(p->cred);
atomic_inc(&p->cred->user->processes);
return 0;
}
new = prepare_creds();
if (!new)
return -ENOMEM;
if (clone_flags & CLONE_NEWUSER) {
ret = create_user_ns(new);
if (ret < 0)
goto error_put;
}
#ifdef CONFIG_KEYS
/* new threads get their own thread keyrings if their parent already
* had one */
if (new->thread_keyring) {
key_put(new->thread_keyring);
new->thread_keyring = NULL;
if (clone_flags & CLONE_THREAD)
install_thread_keyring_to_cred(new);
}
/* we share the process and session keyrings between all the threads in
* a process - this is slightly icky as we violate COW credentials a
* bit */
if (!(clone_flags & CLONE_THREAD)) {
tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
if (!tgcred) {
ret = -ENOMEM;
goto error_put;
}
atomic_set(&tgcred->usage, 1);
spin_lock_init(&tgcred->lock);
tgcred->process_keyring = NULL;
tgcred->session_keyring = key_get(new->tgcred->session_keyring);
release_tgcred(new);
new->tgcred = tgcred;
}
#endif
atomic_inc(&new->user->processes);
p->cred = p->real_cred = get_cred(new);
return 0;
error_put:
put_cred(new);
return ret;
}
/**
* commit_creds - Install new credentials upon the current task
* @new: The credentials to be assigned
*
* Install a new set of credentials to the current task, using RCU to replace
* the old set. Both the objective and the subjective credentials pointers are
* updated. This function may not be called if the subjective credentials are
* in an overridden state.
*
* This function eats the caller's reference to the new credentials.
*
* Always returns 0 thus allowing this function to be tail-called at the end
* of, say, sys_setgid().
*/
int commit_creds(struct cred *new)
{
struct task_struct *task = current;
const struct cred *old;
BUG_ON(task->cred != task->real_cred);
BUG_ON(atomic_read(&task->real_cred->usage) < 2);
BUG_ON(atomic_read(&new->usage) < 1);
old = task->real_cred;
security_commit_creds(new, old);
get_cred(new); /* we will require a ref for the subj creds too */
/* dumpability changes */
if (old->euid != new->euid ||
old->egid != new->egid ||
old->fsuid != new->fsuid ||
old->fsgid != new->fsgid ||
!cap_issubset(new->cap_permitted, old->cap_permitted)) {
set_dumpable(task->mm, suid_dumpable);
task->pdeath_signal = 0;
smp_wmb();
}
/* alter the thread keyring */
if (new->fsuid != old->fsuid)
key_fsuid_changed(task);
if (new->fsgid != old->fsgid)
key_fsgid_changed(task);
/* do it
* - What if a process setreuid()'s and this brings the
* new uid over his NPROC rlimit? We can check this now
* cheaply with the new uid cache, so if it matters
* we should be checking for it. -DaveM
*/
if (new->user != old->user)
atomic_inc(&new->user->processes);
rcu_assign_pointer(task->real_cred, new);
rcu_assign_pointer(task->cred, new);
if (new->user != old->user)
atomic_dec(&old->user->processes);
sched_switch_user(task);
/* send notifications */
if (new->uid != old->uid ||
new->euid != old->euid ||
new->suid != old->suid ||
new->fsuid != old->fsuid)
proc_id_connector(task, PROC_EVENT_UID);
if (new->gid != old->gid ||
new->egid != old->egid ||
new->sgid != old->sgid ||
new->fsgid != old->fsgid)
proc_id_connector(task, PROC_EVENT_GID);
/* release the old obj and subj refs both */
put_cred(old);
put_cred(old);
return 0;
}
EXPORT_SYMBOL(commit_creds);
/**
* abort_creds - Discard a set of credentials and unlock the current task
* @new: The credentials that were going to be applied
*
* Discard a set of credentials that were under construction and unlock the
* current task.
*/
void abort_creds(struct cred *new)
{
BUG_ON(atomic_read(&new->usage) < 1);
put_cred(new);
}
EXPORT_SYMBOL(abort_creds);
/**
* override_creds - Override the current process's subjective credentials
* @new: The credentials to be assigned
*
* Install a set of temporary override subjective credentials on the current
* process, returning the old set for later reversion.
*/
const struct cred *override_creds(const struct cred *new)
{
const struct cred *old = current->cred;
rcu_assign_pointer(current->cred, get_cred(new));
return old;
}
EXPORT_SYMBOL(override_creds);
/**
* revert_creds - Revert a temporary subjective credentials override
* @old: The credentials to be restored
*
* Revert a temporary set of override subjective credentials to an old set,
* discarding the override set.
*/
void revert_creds(const struct cred *old)
{
const struct cred *override = current->cred;
rcu_assign_pointer(current->cred, old);
put_cred(override);
}
EXPORT_SYMBOL(revert_creds);
/*
* initialise the credentials stuff
*/
void __init cred_init(void)
{
/* allocate a slab in which we can store credentials */
cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
}
/**
* prepare_kernel_cred - Prepare a set of credentials for a kernel service
* @daemon: A userspace daemon to be used as a reference
*
* Prepare a set of credentials for a kernel service. This can then be used to
* override a task's own credentials so that work can be done on behalf of that
* task that requires a different subjective context.
*
* @daemon is used to provide a base for the security record, but can be NULL.
* If @daemon is supplied, then the security data will be derived from that;
* otherwise they'll be set to 0 and no groups, full capabilities and no keys.
*
* The caller may change these controls afterwards if desired.
*
* Returns the new credentials or NULL if out of memory.
*
* Does not take, and does not return holding current->cred_replace_mutex.
*/
struct cred *prepare_kernel_cred(struct task_struct *daemon)
{
const struct cred *old;
struct cred *new;
new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
if (!new)
return NULL;
if (daemon)
old = get_task_cred(daemon);
else
old = get_cred(&init_cred);
get_uid(new->user);
get_group_info(new->group_info);
#ifdef CONFIG_KEYS
atomic_inc(&init_tgcred.usage);
new->tgcred = &init_tgcred;
new->request_key_auth = NULL;
new->thread_keyring = NULL;
new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
#endif
#ifdef CONFIG_SECURITY
new->security = NULL;
#endif
if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
goto error;
atomic_set(&new->usage, 1);
put_cred(old);
return new;
error:
put_cred(new);
return NULL;
}
EXPORT_SYMBOL(prepare_kernel_cred);
/**
* set_security_override - Set the security ID in a set of credentials
* @new: The credentials to alter
* @secid: The LSM security ID to set
*
* Set the LSM security ID in a set of credentials so that the subjective
* security is overridden when an alternative set of credentials is used.
*/
int set_security_override(struct cred *new, u32 secid)
{
return security_kernel_act_as(new, secid);
}
EXPORT_SYMBOL(set_security_override);
/**
* set_security_override_from_ctx - Set the security ID in a set of credentials
* @new: The credentials to alter
* @secctx: The LSM security context to generate the security ID from.
*
* Set the LSM security ID in a set of credentials so that the subjective
* security is overridden when an alternative set of credentials is used. The
* security ID is specified in string form as a security context to be
* interpreted by the LSM.
*/
int set_security_override_from_ctx(struct cred *new, const char *secctx)
{
u32 secid;
int ret;
ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
if (ret < 0)
return ret;
return set_security_override(new, secid);
}
EXPORT_SYMBOL(set_security_override_from_ctx);
/**
* set_create_files_as - Set the LSM file create context in a set of credentials
* @new: The credentials to alter
* @inode: The inode to take the context from
*
* Change the LSM file creation context in a set of credentials to be the same
* as the object context of the specified inode, so that the new inodes have
* the same MAC context as that inode.
*/
int set_create_files_as(struct cred *new, struct inode *inode)
{
new->fsuid = inode->i_uid;
new->fsgid = inode->i_gid;
return security_kernel_create_files_as(new, inode);
}
EXPORT_SYMBOL(set_create_files_as);