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>

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 07481bb..c758809 100644 (file)
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -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;

diff --git a/include/uapi/linux/memfd.h b/include/uapi/linux/memfd.h
index 7a8a267..273a4e1 100644 (file)
--- a/include/uapi/linux/memfd.h
+++ b/include/uapi/linux/memfd.h
@@ -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

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index f4f8cb0..8a98b1a 100644 (file)
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -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;
 }
 

diff --git a/kernel/pid_sysctl.h b/kernel/pid_sysctl.h
new file mode 100644 (file)
index 0000000..e22d072
--- /dev/null
+++ b/kernel/pid_sysctl.h
@@ -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 */

diff --git a/mm/memfd.c b/mm/memfd.c
index 4ebeab9..bc21439 100644 (file)
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -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;
        }