mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-12 13:55:32 +00:00
![David Howells](/assets/img/avatar_default.png)
Make execve() take advantage of copy-on-write credentials, allowing it to set up the credentials in advance, and then commit the whole lot after the point of no return. This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). The credential bits from struct linux_binprm are, for the most part, replaced with a single credentials pointer (bprm->cred). This means that all the creds can be calculated in advance and then applied at the point of no return with no possibility of failure. I would like to replace bprm->cap_effective with: cap_isclear(bprm->cap_effective) but this seems impossible due to special behaviour for processes of pid 1 (they always retain their parent's capability masks where normally they'd be changed - see cap_bprm_set_creds()). The following sequence of events now happens: (a) At the start of do_execve, the current task's cred_exec_mutex is locked to prevent PTRACE_ATTACH from obsoleting the calculation of creds that we make. (a) prepare_exec_creds() is then called to make a copy of the current task's credentials and prepare it. This copy is then assigned to bprm->cred. This renders security_bprm_alloc() and security_bprm_free() unnecessary, and so they've been removed. (b) The determination of unsafe execution is now performed immediately after (a) rather than later on in the code. The result is stored in bprm->unsafe for future reference. (c) prepare_binprm() is called, possibly multiple times. (i) This applies the result of set[ug]id binaries to the new creds attached to bprm->cred. Personality bit clearance is recorded, but now deferred on the basis that the exec procedure may yet fail. (ii) This then calls the new security_bprm_set_creds(). This should calculate the new LSM and capability credentials into *bprm->cred. This folds together security_bprm_set() and parts of security_bprm_apply_creds() (these two have been removed). Anything that might fail must be done at this point. (iii) bprm->cred_prepared is set to 1. bprm->cred_prepared is 0 on the first pass of the security calculations, and 1 on all subsequent passes. This allows SELinux in (ii) to base its calculations only on the initial script and not on the interpreter. (d) flush_old_exec() is called to commit the task to execution. This performs the following steps with regard to credentials: (i) Clear pdeath_signal and set dumpable on certain circumstances that may not be covered by commit_creds(). (ii) Clear any bits in current->personality that were deferred from (c.i). (e) install_exec_creds() [compute_creds() as was] is called to install the new credentials. This performs the following steps with regard to credentials: (i) Calls security_bprm_committing_creds() to apply any security requirements, such as flushing unauthorised files in SELinux, that must be done before the credentials are changed. This is made up of bits of security_bprm_apply_creds() and security_bprm_post_apply_creds(), both of which have been removed. This function is not allowed to fail; anything that might fail must have been done in (c.ii). (ii) Calls commit_creds() to apply the new credentials in a single assignment (more or less). Possibly pdeath_signal and dumpable should be part of struct creds. (iii) Unlocks the task's cred_replace_mutex, thus allowing PTRACE_ATTACH to take place. (iv) Clears The bprm->cred pointer as the credentials it was holding are now immutable. (v) Calls security_bprm_committed_creds() to apply any security alterations that must be done after the creds have been changed. SELinux uses this to flush signals and signal handlers. (f) If an error occurs before (d.i), bprm_free() will call abort_creds() to destroy the proposed new credentials and will then unlock cred_replace_mutex. No changes to the credentials will have been made. (2) LSM interface. A number of functions have been changed, added or removed: (*) security_bprm_alloc(), ->bprm_alloc_security() (*) security_bprm_free(), ->bprm_free_security() Removed in favour of preparing new credentials and modifying those. (*) security_bprm_apply_creds(), ->bprm_apply_creds() (*) security_bprm_post_apply_creds(), ->bprm_post_apply_creds() Removed; split between security_bprm_set_creds(), security_bprm_committing_creds() and security_bprm_committed_creds(). (*) security_bprm_set(), ->bprm_set_security() Removed; folded into security_bprm_set_creds(). (*) security_bprm_set_creds(), ->bprm_set_creds() New. The new credentials in bprm->creds should be checked and set up as appropriate. bprm->cred_prepared is 0 on the first call, 1 on the second and subsequent calls. (*) security_bprm_committing_creds(), ->bprm_committing_creds() (*) security_bprm_committed_creds(), ->bprm_committed_creds() New. Apply the security effects of the new credentials. This includes closing unauthorised files in SELinux. This function may not fail. When the former is called, the creds haven't yet been applied to the process; when the latter is called, they have. The former may access bprm->cred, the latter may not. (3) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) The bprm_security_struct struct has been removed in favour of using the credentials-under-construction approach. (c) flush_unauthorized_files() now takes a cred pointer and passes it on to inode_has_perm(), file_has_perm() and dentry_open(). Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Acked-by: Serge Hallyn <serue@us.ibm.com> Signed-off-by: James Morris <jmorris@namei.org>
450 lines
10 KiB
C
450 lines
10 KiB
C
/* Task credentials management
|
|
*
|
|
* 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(3),
|
|
.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().
|
|
*
|
|
* 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->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.
|
|
*/
|
|
int copy_creds(struct task_struct *p, unsigned long clone_flags)
|
|
{
|
|
#ifdef CONFIG_KEYS
|
|
struct thread_group_cred *tgcred;
|
|
#endif
|
|
struct cred *new;
|
|
|
|
mutex_init(&p->cred_exec_mutex);
|
|
|
|
if (
|
|
#ifdef CONFIG_KEYS
|
|
!p->cred->thread_keyring &&
|
|
#endif
|
|
clone_flags & CLONE_THREAD
|
|
) {
|
|
get_cred(p->cred);
|
|
atomic_inc(&p->cred->user->processes);
|
|
return 0;
|
|
}
|
|
|
|
new = prepare_creds();
|
|
if (!new)
|
|
return -ENOMEM;
|
|
|
|
#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) {
|
|
put_cred(new);
|
|
return -ENOMEM;
|
|
}
|
|
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 = new;
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* 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.
|
|
*
|
|
* 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(atomic_read(&new->usage) < 1);
|
|
BUG_ON(atomic_read(&task->cred->usage) < 1);
|
|
|
|
old = task->cred;
|
|
security_commit_creds(new, old);
|
|
|
|
/* 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->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);
|
|
|
|
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 - Temporarily override the current process's credentials
|
|
* @new: The credentials to be assigned
|
|
*
|
|
* Install a set of temporary override 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 credentials override
|
|
* @old: The credentials to be restored
|
|
*
|
|
* Revert a temporary set of override 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);
|
|
}
|