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mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC 

The new MFD_NOEXEC_SEAL and MFD_EXEC flags allows application to set
executable bit at creation time (memfd_create).

When MFD_NOEXEC_SEAL is set, memfd is created without executable bit
(mode:0666), and sealed with F_SEAL_EXEC, so it can't be chmod to be
executable (mode: 0777) after creation.

when MFD_EXEC flag is set, memfd is created with executable bit
(mode:0777), this is the same as the old behavior of memfd_create.

The new pid namespaced sysctl vm.memfd_noexec has 3 values:
0: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL acts like
        MFD_EXEC was set.
1: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL acts like
        MFD_NOEXEC_SEAL was set.
2: memfd_create() without MFD_NOEXEC_SEAL will be rejected.

The sysctl allows finer control of memfd_create for old-software that
doesn't set the executable bit, for example, a container with
vm.memfd_noexec=1 means the old-software will create non-executable memfd
by default.  Also, the value of memfd_noexec is passed to child namespace
at creation time.  For example, if the init namespace has
vm.memfd_noexec=2, all its children namespaces will be created with 2.

[akpm@linux-foundation.org: add stub functions to fix build]
[akpm@linux-foundation.org: remove unneeded register_pid_ns_ctl_table_vm() stub, per Jeff]
[akpm@linux-foundation.org: s/pr_warn_ratelimited/pr_warn_once/, per review]
[akpm@linux-foundation.org: fix CONFIG_SYSCTL=n warning]
Link: https://lkml.kernel.org/r/20221215001205.51969-4-jeffxu@google.com
Signed-off-by: Jeff Xu <jeffxu@google.com>
Co-developed-by: Daniel Verkamp <dverkamp@chromium.org>
Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jorge Lucangeli Obes <jorgelo@chromium.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jeff Xu 2022-12-15 00:12:03 +00:00 committed by Andrew Morton
parent 32d118ad50
commit 105ff5339f
5 changed files with 134 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
include/linux/pid_namespace.h
View File

@ -16,6 +16,21 @@
struct fs_pin;
#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
/*
* sysctl for vm.memfd_noexec
* 0: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL
* acts like MFD_EXEC was set.
* 1: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL
* acts like MFD_NOEXEC_SEAL was set.
* 2: memfd_create() without MFD_NOEXEC_SEAL will be
* rejected.
*/
#define MEMFD_NOEXEC_SCOPE_EXEC 0
#define MEMFD_NOEXEC_SCOPE_NOEXEC_SEAL 1
#define MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED 2
#endif
struct pid_namespace {
struct idr idr;
struct rcu_head rcu;
@ -31,6 +46,10 @@ struct pid_namespace {
struct ucounts *ucounts;
int reboot; /* group exit code if this pidns was rebooted */
struct ns_common ns;
#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
/* sysctl for vm.memfd_noexec */
int memfd_noexec_scope;
#endif
} __randomize_layout;
extern struct pid_namespace init_pid_ns;

4
include/uapi/linux/memfd.h
View File

@ -8,6 +8,10 @@
#define MFD_CLOEXEC 0x0001U
#define MFD_ALLOW_SEALING 0x0002U
#define MFD_HUGETLB 0x0004U
/* not executable and sealed to prevent changing to executable. */
#define MFD_NOEXEC_SEAL 0x0008U
/* executable */
#define MFD_EXEC 0x0010U
/*
* Huge page size encoding when MFD_HUGETLB is specified, and a huge page

5
kernel/pid_namespace.c
View File

@ -23,6 +23,7 @@
#include <linux/sched/task.h>
#include <linux/sched/signal.h>
#include <linux/idr.h>
#include "pid_sysctl.h"
static DEFINE_MUTEX(pid_caches_mutex);
static struct kmem_cache *pid_ns_cachep;
@ -110,6 +111,8 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
ns->ucounts = ucounts;
ns->pid_allocated = PIDNS_ADDING;
initialize_memfd_noexec_scope(ns);
return ns;
out_free_idr:
@ -455,6 +458,8 @@ static __init int pid_namespaces_init(void)
#ifdef CONFIG_CHECKPOINT_RESTORE
register_sysctl_paths(kern_path, pid_ns_ctl_table);
#endif
register_pid_ns_sysctl_table_vm();
return 0;
}

60
kernel/pid_sysctl.h Normal file
View File

@ -0,0 +1,60 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef LINUX_PID_SYSCTL_H
#define LINUX_PID_SYSCTL_H
#include <linux/pid_namespace.h>
#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
static inline void initialize_memfd_noexec_scope(struct pid_namespace *ns)
{
ns->memfd_noexec_scope =
task_active_pid_ns(current)->memfd_noexec_scope;
}
static int pid_mfd_noexec_dointvec_minmax(struct ctl_table *table,
int write, void *buf, size_t *lenp, loff_t *ppos)
{
struct pid_namespace *ns = task_active_pid_ns(current);
struct ctl_table table_copy;
if (write && !ns_capable(ns->user_ns, CAP_SYS_ADMIN))
return -EPERM;
table_copy = *table;
if (ns != &init_pid_ns)
table_copy.data = &ns->memfd_noexec_scope;
/*
* set minimum to current value, the effect is only bigger
* value is accepted.
*/
if (*(int *)table_copy.data > *(int *)table_copy.extra1)
table_copy.extra1 = table_copy.data;
return proc_dointvec_minmax(&table_copy, write, buf, lenp, ppos);
}
static struct ctl_table pid_ns_ctl_table_vm[] = {
{
.procname = "memfd_noexec",
.data = &init_pid_ns.memfd_noexec_scope,
.maxlen = sizeof(init_pid_ns.memfd_noexec_scope),
.mode = 0644,
.proc_handler = pid_mfd_noexec_dointvec_minmax,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_TWO,
},
{ }
};
static struct ctl_path vm_path[] = { { .procname = "vm", }, { } };
static inline void register_pid_ns_sysctl_table_vm(void)
{
register_sysctl_paths(vm_path, pid_ns_ctl_table_vm);
}
#else
static inline void initialize_memfd_noexec_scope(struct pid_namespace *ns) {}
static inline void set_memfd_noexec_scope(struct pid_namespace *ns) {}
static inline void register_pid_ns_sysctl_table_vm(void) {}
#endif
#endif /* LINUX_PID_SYSCTL_H */

48
mm/memfd.c
View File

@ -18,6 +18,7 @@
#include <linux/hugetlb.h>
#include <linux/shmem_fs.h>
#include <linux/memfd.h>
#include <linux/pid_namespace.h>
#include <uapi/linux/memfd.h>
/*
@ -263,12 +264,13 @@ long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)
#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | MFD_NOEXEC_SEAL | MFD_EXEC)
SYSCALL_DEFINE2(memfd_create,
const char __user *, uname,
unsigned int, flags)
{
char comm[TASK_COMM_LEN];
unsigned int *file_seals;
struct file *file;
int fd, error;
@ -285,6 +287,40 @@ SYSCALL_DEFINE2(memfd_create,
return -EINVAL;
}
/* Invalid if both EXEC and NOEXEC_SEAL are set.*/
if ((flags & MFD_EXEC) && (flags & MFD_NOEXEC_SEAL))
return -EINVAL;
if (!(flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
#ifdef CONFIG_SYSCTL
int sysctl = MEMFD_NOEXEC_SCOPE_EXEC;
struct pid_namespace *ns;
ns = task_active_pid_ns(current);
if (ns)
sysctl = ns->memfd_noexec_scope;
switch (sysctl) {
case MEMFD_NOEXEC_SCOPE_EXEC:
flags |= MFD_EXEC;
break;
case MEMFD_NOEXEC_SCOPE_NOEXEC_SEAL:
flags |= MFD_NOEXEC_SEAL;
break;
default:
pr_warn_once(
"memfd_create(): MFD_NOEXEC_SEAL is enforced, pid=%d '%s'\n",
task_pid_nr(current), get_task_comm(comm, current));
return -EINVAL;
}
#else
flags |= MFD_EXEC;
#endif
pr_warn_once(
"memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=%d '%s'\n",
task_pid_nr(current), get_task_comm(comm, current));
}
/* length includes terminating zero */
len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
if (len <= 0)
@ -328,7 +364,15 @@ SYSCALL_DEFINE2(memfd_create,
file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
file->f_flags |= O_LARGEFILE;
if (flags & MFD_ALLOW_SEALING) {
if (flags & MFD_NOEXEC_SEAL) {
struct inode *inode = file_inode(file);
inode->i_mode &= ~0111;
file_seals = memfd_file_seals_ptr(file);
*file_seals &= ~F_SEAL_SEAL;
*file_seals |= F_SEAL_EXEC;
} else if (flags & MFD_ALLOW_SEALING) {
/* MFD_EXEC and MFD_ALLOW_SEALING are set */
file_seals = memfd_file_seals_ptr(file);
*file_seals &= ~F_SEAL_SEAL;
}