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