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linux/kernel/nsproxy.c
Andrei Vagin 133e2d3e81 fs/exec: allow to unshare a time namespace on vfork+exec 
Right now, a new process can't be forked in another time namespace
if it shares mm with its parent. It is prohibited, because each time
namespace has its own vvar page that is mapped into a process address
space.

When a process calls exec, it gets a new mm and so it could be "legal"
to switch time namespace in that case. This was not implemented and
now if we want to do this, we need to add another clone flag to not
break backward compatibility.

We don't have any user requests to switch times on exec except the
vfork+exec combination, so there is no reason to add a new clone flag.
As for vfork+exec, this should be safe to allow switching timens with
the current clone flag. Right now, vfork (CLONE_VFORK | CLONE_VM) fails
if a child is forked into another time namespace. With this change,
vfork creates a new process in parent's timens, and the following exec
does the actual switch to the target time namespace.

Suggested-by: Florian Weimer <fweimer@redhat.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220613060723.197407-1-avagin@gmail.com
2022-06-15 07:58:04 -07:00

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// 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 = ATOMIC_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)
atomic_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 (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);
}
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 file *file;
struct ns_common *ns = NULL;
struct nsset nsset = {};
int err = 0;
file = fget(fd);
if (!file)
return -EBADF;
if (proc_ns_file(file)) {
ns = get_proc_ns(file_inode(file));
if (flags && (ns->ops->type != flags))
err = -EINVAL;
flags = ns->ops->type;
} else if (!IS_ERR(pidfd_pid(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(file))
err = validate_ns(&nsset, ns);
else
err = validate_nsset(&nsset, file->private_data);
if (!err) {
commit_nsset(&nsset);
perf_event_namespaces(current);
}
put_nsset(&nsset);
out:
fput(file);
return err;
}
int __init nsproxy_cache_init(void)
{
nsproxy_cachep = KMEM_CACHE(nsproxy, SLAB_PANIC|SLAB_ACCOUNT);
return 0;
}
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