linux/kernel/nsproxy.c
Elena Reshetova 2ddd3cac1f nsproxy: Convert nsproxy.count to refcount_t
atomic_t variables are currently used to implement reference counters
with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows and
underflows. This is important since overflows and underflows can lead
to use-after-free situation and be exploitable.

The variable nsproxy.count is used as pure reference counter. Convert it
to refcount_t and fix up the operations.

**Important note for maintainers:

Some functions from refcount_t API defined in refcount.h have different
memory ordering guarantees than their atomic counterparts. Please check
Documentation/core-api/refcount-vs-atomic.rst for more information.

Normally the differences should not matter since refcount_t provides
enough guarantees to satisfy the refcounting use cases, but in some
rare cases it might matter. Please double check that you don't have
some undocumented memory guarantees for this variable usage.

For the nsproxy.count it might make a difference in following places:
 - put_nsproxy() and switch_task_namespaces(): decrement in
   refcount_dec_and_test() only provides RELEASE ordering and ACQUIRE
   ordering on success vs. fully ordered atomic counterpart

Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230818041327.gonna.210-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
2023-08-21 11:29:12 -07:00

592 lines
13 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2006 IBM Corporation
*
* Author: Serge Hallyn <serue@us.ibm.com>
*
* Jun 2006 - namespaces support
* OpenVZ, SWsoft Inc.
* Pavel Emelianov <xemul@openvz.org>
*/
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/nsproxy.h>
#include <linux/init_task.h>
#include <linux/mnt_namespace.h>
#include <linux/utsname.h>
#include <linux/pid_namespace.h>
#include <net/net_namespace.h>
#include <linux/ipc_namespace.h>
#include <linux/time_namespace.h>
#include <linux/fs_struct.h>
#include <linux/proc_fs.h>
#include <linux/proc_ns.h>
#include <linux/file.h>
#include <linux/syscalls.h>
#include <linux/cgroup.h>
#include <linux/perf_event.h>
static struct kmem_cache *nsproxy_cachep;
struct nsproxy init_nsproxy = {
.count = REFCOUNT_INIT(1),
.uts_ns = &init_uts_ns,
#if defined(CONFIG_POSIX_MQUEUE) || defined(CONFIG_SYSVIPC)
.ipc_ns = &init_ipc_ns,
#endif
.mnt_ns = NULL,
.pid_ns_for_children = &init_pid_ns,
#ifdef CONFIG_NET
.net_ns = &init_net,
#endif
#ifdef CONFIG_CGROUPS
.cgroup_ns = &init_cgroup_ns,
#endif
#ifdef CONFIG_TIME_NS
.time_ns = &init_time_ns,
.time_ns_for_children = &init_time_ns,
#endif
};
static inline struct nsproxy *create_nsproxy(void)
{
struct nsproxy *nsproxy;
nsproxy = kmem_cache_alloc(nsproxy_cachep, GFP_KERNEL);
if (nsproxy)
refcount_set(&nsproxy->count, 1);
return nsproxy;
}
/*
* Create new nsproxy and all of its the associated namespaces.
* Return the newly created nsproxy. Do not attach this to the task,
* leave it to the caller to do proper locking and attach it to task.
*/
static struct nsproxy *create_new_namespaces(unsigned long flags,
struct task_struct *tsk, struct user_namespace *user_ns,
struct fs_struct *new_fs)
{
struct nsproxy *new_nsp;
int err;
new_nsp = create_nsproxy();
if (!new_nsp)
return ERR_PTR(-ENOMEM);
new_nsp->mnt_ns = copy_mnt_ns(flags, tsk->nsproxy->mnt_ns, user_ns, new_fs);
if (IS_ERR(new_nsp->mnt_ns)) {
err = PTR_ERR(new_nsp->mnt_ns);
goto out_ns;
}
new_nsp->uts_ns = copy_utsname(flags, user_ns, tsk->nsproxy->uts_ns);
if (IS_ERR(new_nsp->uts_ns)) {
err = PTR_ERR(new_nsp->uts_ns);
goto out_uts;
}
new_nsp->ipc_ns = copy_ipcs(flags, user_ns, tsk->nsproxy->ipc_ns);
if (IS_ERR(new_nsp->ipc_ns)) {
err = PTR_ERR(new_nsp->ipc_ns);
goto out_ipc;
}
new_nsp->pid_ns_for_children =
copy_pid_ns(flags, user_ns, tsk->nsproxy->pid_ns_for_children);
if (IS_ERR(new_nsp->pid_ns_for_children)) {
err = PTR_ERR(new_nsp->pid_ns_for_children);
goto out_pid;
}
new_nsp->cgroup_ns = copy_cgroup_ns(flags, user_ns,
tsk->nsproxy->cgroup_ns);
if (IS_ERR(new_nsp->cgroup_ns)) {
err = PTR_ERR(new_nsp->cgroup_ns);
goto out_cgroup;
}
new_nsp->net_ns = copy_net_ns(flags, user_ns, tsk->nsproxy->net_ns);
if (IS_ERR(new_nsp->net_ns)) {
err = PTR_ERR(new_nsp->net_ns);
goto out_net;
}
new_nsp->time_ns_for_children = copy_time_ns(flags, user_ns,
tsk->nsproxy->time_ns_for_children);
if (IS_ERR(new_nsp->time_ns_for_children)) {
err = PTR_ERR(new_nsp->time_ns_for_children);
goto out_time;
}
new_nsp->time_ns = get_time_ns(tsk->nsproxy->time_ns);
return new_nsp;
out_time:
put_net(new_nsp->net_ns);
out_net:
put_cgroup_ns(new_nsp->cgroup_ns);
out_cgroup:
if (new_nsp->pid_ns_for_children)
put_pid_ns(new_nsp->pid_ns_for_children);
out_pid:
if (new_nsp->ipc_ns)
put_ipc_ns(new_nsp->ipc_ns);
out_ipc:
if (new_nsp->uts_ns)
put_uts_ns(new_nsp->uts_ns);
out_uts:
if (new_nsp->mnt_ns)
put_mnt_ns(new_nsp->mnt_ns);
out_ns:
kmem_cache_free(nsproxy_cachep, new_nsp);
return ERR_PTR(err);
}
/*
* called from clone. This now handles copy for nsproxy and all
* namespaces therein.
*/
int copy_namespaces(unsigned long flags, struct task_struct *tsk)
{
struct nsproxy *old_ns = tsk->nsproxy;
struct user_namespace *user_ns = task_cred_xxx(tsk, user_ns);
struct nsproxy *new_ns;
if (likely(!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
CLONE_NEWPID | CLONE_NEWNET |
CLONE_NEWCGROUP | CLONE_NEWTIME)))) {
if ((flags & CLONE_VM) ||
likely(old_ns->time_ns_for_children == old_ns->time_ns)) {
get_nsproxy(old_ns);
return 0;
}
} else if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;
/*
* CLONE_NEWIPC must detach from the undolist: after switching
* to a new ipc namespace, the semaphore arrays from the old
* namespace are unreachable. In clone parlance, CLONE_SYSVSEM
* means share undolist with parent, so we must forbid using
* it along with CLONE_NEWIPC.
*/
if ((flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
(CLONE_NEWIPC | CLONE_SYSVSEM))
return -EINVAL;
new_ns = create_new_namespaces(flags, tsk, user_ns, tsk->fs);
if (IS_ERR(new_ns))
return PTR_ERR(new_ns);
if ((flags & CLONE_VM) == 0)
timens_on_fork(new_ns, tsk);
tsk->nsproxy = new_ns;
return 0;
}
void free_nsproxy(struct nsproxy *ns)
{
if (ns->mnt_ns)
put_mnt_ns(ns->mnt_ns);
if (ns->uts_ns)
put_uts_ns(ns->uts_ns);
if (ns->ipc_ns)
put_ipc_ns(ns->ipc_ns);
if (ns->pid_ns_for_children)
put_pid_ns(ns->pid_ns_for_children);
if (ns->time_ns)
put_time_ns(ns->time_ns);
if (ns->time_ns_for_children)
put_time_ns(ns->time_ns_for_children);
put_cgroup_ns(ns->cgroup_ns);
put_net(ns->net_ns);
kmem_cache_free(nsproxy_cachep, ns);
}
/*
* Called from unshare. Unshare all the namespaces part of nsproxy.
* On success, returns the new nsproxy.
*/
int unshare_nsproxy_namespaces(unsigned long unshare_flags,
struct nsproxy **new_nsp, struct cred *new_cred, struct fs_struct *new_fs)
{
struct user_namespace *user_ns;
int err = 0;
if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
CLONE_NEWNET | CLONE_NEWPID | CLONE_NEWCGROUP |
CLONE_NEWTIME)))
return 0;
user_ns = new_cred ? new_cred->user_ns : current_user_ns();
if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;
*new_nsp = create_new_namespaces(unshare_flags, current, user_ns,
new_fs ? new_fs : current->fs);
if (IS_ERR(*new_nsp)) {
err = PTR_ERR(*new_nsp);
goto out;
}
out:
return err;
}
void switch_task_namespaces(struct task_struct *p, struct nsproxy *new)
{
struct nsproxy *ns;
might_sleep();
task_lock(p);
ns = p->nsproxy;
p->nsproxy = new;
task_unlock(p);
if (ns)
put_nsproxy(ns);
}
void exit_task_namespaces(struct task_struct *p)
{
switch_task_namespaces(p, NULL);
}
int exec_task_namespaces(void)
{
struct task_struct *tsk = current;
struct nsproxy *new;
if (tsk->nsproxy->time_ns_for_children == tsk->nsproxy->time_ns)
return 0;
new = create_new_namespaces(0, tsk, current_user_ns(), tsk->fs);
if (IS_ERR(new))
return PTR_ERR(new);
timens_on_fork(new, tsk);
switch_task_namespaces(tsk, new);
return 0;
}
static int check_setns_flags(unsigned long flags)
{
if (!flags || (flags & ~(CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
CLONE_NEWNET | CLONE_NEWTIME | CLONE_NEWUSER |
CLONE_NEWPID | CLONE_NEWCGROUP)))
return -EINVAL;
#ifndef CONFIG_USER_NS
if (flags & CLONE_NEWUSER)
return -EINVAL;
#endif
#ifndef CONFIG_PID_NS
if (flags & CLONE_NEWPID)
return -EINVAL;
#endif
#ifndef CONFIG_UTS_NS
if (flags & CLONE_NEWUTS)
return -EINVAL;
#endif
#ifndef CONFIG_IPC_NS
if (flags & CLONE_NEWIPC)
return -EINVAL;
#endif
#ifndef CONFIG_CGROUPS
if (flags & CLONE_NEWCGROUP)
return -EINVAL;
#endif
#ifndef CONFIG_NET_NS
if (flags & CLONE_NEWNET)
return -EINVAL;
#endif
#ifndef CONFIG_TIME_NS
if (flags & CLONE_NEWTIME)
return -EINVAL;
#endif
return 0;
}
static void put_nsset(struct nsset *nsset)
{
unsigned flags = nsset->flags;
if (flags & CLONE_NEWUSER)
put_cred(nsset_cred(nsset));
/*
* We only created a temporary copy if we attached to more than just
* the mount namespace.
*/
if (nsset->fs && (flags & CLONE_NEWNS) && (flags & ~CLONE_NEWNS))
free_fs_struct(nsset->fs);
if (nsset->nsproxy)
free_nsproxy(nsset->nsproxy);
}
static int prepare_nsset(unsigned flags, struct nsset *nsset)
{
struct task_struct *me = current;
nsset->nsproxy = create_new_namespaces(0, me, current_user_ns(), me->fs);
if (IS_ERR(nsset->nsproxy))
return PTR_ERR(nsset->nsproxy);
if (flags & CLONE_NEWUSER)
nsset->cred = prepare_creds();
else
nsset->cred = current_cred();
if (!nsset->cred)
goto out;
/* Only create a temporary copy of fs_struct if we really need to. */
if (flags == CLONE_NEWNS) {
nsset->fs = me->fs;
} else if (flags & CLONE_NEWNS) {
nsset->fs = copy_fs_struct(me->fs);
if (!nsset->fs)
goto out;
}
nsset->flags = flags;
return 0;
out:
put_nsset(nsset);
return -ENOMEM;
}
static inline int validate_ns(struct nsset *nsset, struct ns_common *ns)
{
return ns->ops->install(nsset, ns);
}
/*
* This is the inverse operation to unshare().
* Ordering is equivalent to the standard ordering used everywhere else
* during unshare and process creation. The switch to the new set of
* namespaces occurs at the point of no return after installation of
* all requested namespaces was successful in commit_nsset().
*/
static int validate_nsset(struct nsset *nsset, struct pid *pid)
{
int ret = 0;
unsigned flags = nsset->flags;
struct user_namespace *user_ns = NULL;
struct pid_namespace *pid_ns = NULL;
struct nsproxy *nsp;
struct task_struct *tsk;
/* Take a "snapshot" of the target task's namespaces. */
rcu_read_lock();
tsk = pid_task(pid, PIDTYPE_PID);
if (!tsk) {
rcu_read_unlock();
return -ESRCH;
}
if (!ptrace_may_access(tsk, PTRACE_MODE_READ_REALCREDS)) {
rcu_read_unlock();
return -EPERM;
}
task_lock(tsk);
nsp = tsk->nsproxy;
if (nsp)
get_nsproxy(nsp);
task_unlock(tsk);
if (!nsp) {
rcu_read_unlock();
return -ESRCH;
}
#ifdef CONFIG_PID_NS
if (flags & CLONE_NEWPID) {
pid_ns = task_active_pid_ns(tsk);
if (unlikely(!pid_ns)) {
rcu_read_unlock();
ret = -ESRCH;
goto out;
}
get_pid_ns(pid_ns);
}
#endif
#ifdef CONFIG_USER_NS
if (flags & CLONE_NEWUSER)
user_ns = get_user_ns(__task_cred(tsk)->user_ns);
#endif
rcu_read_unlock();
/*
* Install requested namespaces. The caller will have
* verified earlier that the requested namespaces are
* supported on this kernel. We don't report errors here
* if a namespace is requested that isn't supported.
*/
#ifdef CONFIG_USER_NS
if (flags & CLONE_NEWUSER) {
ret = validate_ns(nsset, &user_ns->ns);
if (ret)
goto out;
}
#endif
if (flags & CLONE_NEWNS) {
ret = validate_ns(nsset, from_mnt_ns(nsp->mnt_ns));
if (ret)
goto out;
}
#ifdef CONFIG_UTS_NS
if (flags & CLONE_NEWUTS) {
ret = validate_ns(nsset, &nsp->uts_ns->ns);
if (ret)
goto out;
}
#endif
#ifdef CONFIG_IPC_NS
if (flags & CLONE_NEWIPC) {
ret = validate_ns(nsset, &nsp->ipc_ns->ns);
if (ret)
goto out;
}
#endif
#ifdef CONFIG_PID_NS
if (flags & CLONE_NEWPID) {
ret = validate_ns(nsset, &pid_ns->ns);
if (ret)
goto out;
}
#endif
#ifdef CONFIG_CGROUPS
if (flags & CLONE_NEWCGROUP) {
ret = validate_ns(nsset, &nsp->cgroup_ns->ns);
if (ret)
goto out;
}
#endif
#ifdef CONFIG_NET_NS
if (flags & CLONE_NEWNET) {
ret = validate_ns(nsset, &nsp->net_ns->ns);
if (ret)
goto out;
}
#endif
#ifdef CONFIG_TIME_NS
if (flags & CLONE_NEWTIME) {
ret = validate_ns(nsset, &nsp->time_ns->ns);
if (ret)
goto out;
}
#endif
out:
if (pid_ns)
put_pid_ns(pid_ns);
if (nsp)
put_nsproxy(nsp);
put_user_ns(user_ns);
return ret;
}
/*
* This is the point of no return. There are just a few namespaces
* that do some actual work here and it's sufficiently minimal that
* a separate ns_common operation seems unnecessary for now.
* Unshare is doing the same thing. If we'll end up needing to do
* more in a given namespace or a helper here is ultimately not
* exported anymore a simple commit handler for each namespace
* should be added to ns_common.
*/
static void commit_nsset(struct nsset *nsset)
{
unsigned flags = nsset->flags;
struct task_struct *me = current;
#ifdef CONFIG_USER_NS
if (flags & CLONE_NEWUSER) {
/* transfer ownership */
commit_creds(nsset_cred(nsset));
nsset->cred = NULL;
}
#endif
/* We only need to commit if we have used a temporary fs_struct. */
if ((flags & CLONE_NEWNS) && (flags & ~CLONE_NEWNS)) {
set_fs_root(me->fs, &nsset->fs->root);
set_fs_pwd(me->fs, &nsset->fs->pwd);
}
#ifdef CONFIG_IPC_NS
if (flags & CLONE_NEWIPC)
exit_sem(me);
#endif
#ifdef CONFIG_TIME_NS
if (flags & CLONE_NEWTIME)
timens_commit(me, nsset->nsproxy->time_ns);
#endif
/* transfer ownership */
switch_task_namespaces(me, nsset->nsproxy);
nsset->nsproxy = NULL;
}
SYSCALL_DEFINE2(setns, int, fd, int, flags)
{
struct fd f = fdget(fd);
struct ns_common *ns = NULL;
struct nsset nsset = {};
int err = 0;
if (!f.file)
return -EBADF;
if (proc_ns_file(f.file)) {
ns = get_proc_ns(file_inode(f.file));
if (flags && (ns->ops->type != flags))
err = -EINVAL;
flags = ns->ops->type;
} else if (!IS_ERR(pidfd_pid(f.file))) {
err = check_setns_flags(flags);
} else {
err = -EINVAL;
}
if (err)
goto out;
err = prepare_nsset(flags, &nsset);
if (err)
goto out;
if (proc_ns_file(f.file))
err = validate_ns(&nsset, ns);
else
err = validate_nsset(&nsset, f.file->private_data);
if (!err) {
commit_nsset(&nsset);
perf_event_namespaces(current);
}
put_nsset(&nsset);
out:
fdput(f);
return err;
}
int __init nsproxy_cache_init(void)
{
nsproxy_cachep = KMEM_CACHE(nsproxy, SLAB_PANIC|SLAB_ACCOUNT);
return 0;
}