[PATCH v5 0/6] mm/memfd: introduce MFD_NOEXEC_SEAL and MFD_EXEC

[PATCH v5 0/6] mm/memfd: introduce MFD_NOEXEC_SEAL and MFD_EXEC

[jeffxu]

From: Jeff Xu <jeffxu@chromium.org>

Since Linux introduced the memfd feature, memfd have always had their execute bit set, and the memfd_create() syscall doesn't allow setting it differently.

However, in a secure by default system, such as ChromeOS, (where all executables should come from the rootfs, which is protected by Verified boot), this executable nature of memfd opens a door for NoExec bypass and enables “confused deputy attack”.  E.g, in VRP bug [1]: cros_vm process created a memfd to share the content with an external process, however the memfd is overwritten and used for executing arbitrary code and root escalation. [2] lists more VRP in this kind.

On the other hand, executable memfd has its legit use, runc uses memfd’s seal and executable feature to copy the contents of the binary then execute them, for such system, we need a solution to differentiate runc's use of  executable memfds and an attacker's [3].

To address those above, this set of patches add following:
1> Let memfd_create() set X bit at creation time.
2> Let memfd to be sealed for modifying X bit.
3> A new pid namespace sysctl: vm.memfd_noexec to control behavior of X bit.  For example, if a container has vm.memfd_noexec=2, then memfd_create() without MFD_NOEXEC_SEAL will be rejected.
4> A new security hook in memfd_create(). This make it possible to a new LSM, which rejects or allows executable memfd based on its security policy.

This is V4 version of patch: see [4] [5] [6] for previous versions.

[1] https://crbug.com/1305411
[2] https://bugs.chromium.org/p/chromium/issues/list?q=type%3Dbug-security%20memfd%20escalation&can=1
[3] https://lwn.net/Articles/781013/
[4] https://lwn.net/Articles/890096/
[5] https://lore.kernel.org/lkml/20220805222126.142525-1-jeffxu@chromium.org/
[6] https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@chromium.org/

Daniel Verkamp (2):
  mm/memfd: add F_SEAL_EXEC
  selftests/memfd: add tests for F_SEAL_EXEC

Jeff Xu (4):
  mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC
  mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd
  selftests/memfd: add tests for MFD_NOEXEC_SEAL MFD_EXEC
  mm/memfd: security hook for memfd_create

 include/linux/lsm_hook_defs.h              |   1 +
 include/linux/lsm_hooks.h                  |   4 +
 include/linux/pid_namespace.h              |  19 ++
 include/linux/security.h                   |   6 +
 include/uapi/linux/fcntl.h                 |   1 +
 include/uapi/linux/memfd.h                 |   4 +
 kernel/pid_namespace.c                     |  48 ++++
 mm/memfd.c                                 |  61 ++++-
 mm/shmem.c                                 |   6 +
 security/security.c                        |  13 +
 tools/testing/selftests/memfd/fuse_test.c  |   1 +
 tools/testing/selftests/memfd/memfd_test.c | 304 ++++++++++++++++++++-
 12 files changed, 465 insertions(+), 3 deletions(-)


base-commit: eb7081409f94a9a8608593d0fb63a1aa3d6f95d8
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

[PATCH v5 1/6] mm/memfd: add F_SEAL_EXEC

[jeffxu]

From: Daniel Verkamp <dverkamp@chromium.org>

The new F_SEAL_EXEC flag will prevent modification of the exec bits:
written as traditional octal mask, 0111, or as named flags, S_IXUSR |
S_IXGRP | S_IXOTH. Any chmod(2) or similar call that attempts to modify
any of these bits after the seal is applied will fail with errno EPERM.

This will preserve the execute bits as they are at the time of sealing,
so the memfd will become either permanently executable or permanently
un-executable.

Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
Co-developed-by: Jeff Xu <jeffxu@chromium.org>
Signed-off-by: Jeff Xu <jeffxu@chromium.org>
---
 include/uapi/linux/fcntl.h | 1 +
 mm/memfd.c                 | 2 ++
 mm/shmem.c                 | 6 ++++++
 3 files changed, 9 insertions(+)

diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 2f86b2ad6d7e..e8c07da58c9f 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -43,6 +43,7 @@
 #define F_SEAL_GROW	0x0004	/* prevent file from growing */
 #define F_SEAL_WRITE	0x0008	/* prevent writes */
 #define F_SEAL_FUTURE_WRITE	0x0010  /* prevent future writes while mapped */
+#define F_SEAL_EXEC	0x0020  /* prevent chmod modifying exec bits */
 /* (1U << 31) is reserved for signed error codes */
 
 /*
diff --git a/mm/memfd.c b/mm/memfd.c
index 08f5f8304746..4ebeab94aa74 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -147,6 +147,7 @@ static unsigned int *memfd_file_seals_ptr(struct file *file)
 }
 
 #define F_ALL_SEALS (F_SEAL_SEAL | \
+		     F_SEAL_EXEC | \
 		     F_SEAL_SHRINK | \
 		     F_SEAL_GROW | \
 		     F_SEAL_WRITE | \
@@ -175,6 +176,7 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 	 *   SEAL_SHRINK: Prevent the file from shrinking
 	 *   SEAL_GROW: Prevent the file from growing
 	 *   SEAL_WRITE: Prevent write access to the file
+	 *   SEAL_EXEC: Prevent modification of the exec bits in the file mode
 	 *
 	 * As we don't require any trust relationship between two parties, we
 	 * must prevent seals from being removed. Therefore, sealing a file
diff --git a/mm/shmem.c b/mm/shmem.c
index c1d8b8a1aa3b..e18a9cf9d937 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1085,6 +1085,12 @@ static int shmem_setattr(struct user_namespace *mnt_userns,
 	if (error)
 		return error;
 
+	if ((info->seals & F_SEAL_EXEC) && (attr->ia_valid & ATTR_MODE)) {
+		if ((inode->i_mode ^ attr->ia_mode) & 0111) {
+			return -EPERM;
+		}
+	}
+
 	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
 		loff_t oldsize = inode->i_size;
 		loff_t newsize = attr->ia_size;
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

[PATCH v5 2/6] selftests/memfd: add tests for F_SEAL_EXEC

[jeffxu]

From: Daniel Verkamp <dverkamp@chromium.org>

Basic tests to ensure that user/group/other execute bits cannot be
changed after applying F_SEAL_EXEC to a memfd.

Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
Co-developed-by: Jeff Xu <jeffxu@chromium.org>
Signed-off-by: Jeff Xu <jeffxu@chromium.org>
---
 tools/testing/selftests/memfd/memfd_test.c | 129 ++++++++++++++++++++-
 1 file changed, 128 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index 94df2692e6e4..1d7e7b36bbdd 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -28,12 +28,44 @@
 #define MFD_DEF_SIZE 8192
 #define STACK_SIZE 65536
 
+#ifndef F_SEAL_EXEC
+#define F_SEAL_EXEC	0x0020
+#endif
+
+#ifndef MAX_PATH
+#define MAX_PATH 256
+#endif
+
 /*
  * Default is not to test hugetlbfs
  */
 static size_t mfd_def_size = MFD_DEF_SIZE;
 static const char *memfd_str = MEMFD_STR;
 
+static ssize_t fd2name(int fd, char *buf, size_t bufsize)
+{
+	char buf1[MAX_PATH];
+	int size;
+	ssize_t nbytes;
+
+	size = snprintf(buf1, MAX_PATH, "/proc/self/fd/%d", fd);
+	if (size < 0) {
+		printf("snprintf(%d) failed on %m\n", fd);
+		abort();
+	}
+
+	/*
+	 * reserver one byte for string termination.
+	 */
+	nbytes = readlink(buf1, buf, bufsize-1);
+	if (nbytes == -1) {
+		printf("readlink(%s) failed %m\n", buf1);
+		abort();
+	}
+	buf[nbytes] = '\0';
+	return nbytes;
+}
+
 static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags)
 {
 	int r, fd;
@@ -98,11 +130,14 @@ static unsigned int mfd_assert_get_seals(int fd)
 
 static void mfd_assert_has_seals(int fd, unsigned int seals)
 {
+	char buf[MAX_PATH];
+	int nbytes;
 	unsigned int s;
+	fd2name(fd, buf, MAX_PATH);
 
 	s = mfd_assert_get_seals(fd);
 	if (s != seals) {
-		printf("%u != %u = GET_SEALS(%d)\n", seals, s, fd);
+		printf("%u != %u = GET_SEALS(%s)\n", seals, s, buf);
 		abort();
 	}
 }
@@ -594,6 +629,64 @@ static void mfd_fail_grow_write(int fd)
 	}
 }
 
+static void mfd_assert_mode(int fd, int mode)
+{
+	struct stat st;
+	char buf[MAX_PATH];
+	int nbytes;
+
+	fd2name(fd, buf, MAX_PATH);
+
+	if (fstat(fd, &st) < 0) {
+		printf("fstat(%s) failed: %m\n", buf);
+		abort();
+	}
+
+	if ((st.st_mode & 07777) != mode) {
+		printf("fstat(%s) wrong file mode 0%04o, but expected 0%04o\n",
+		       buf, (int)st.st_mode & 07777, mode);
+		abort();
+	}
+}
+
+static void mfd_assert_chmod(int fd, int mode)
+{
+	char buf[MAX_PATH];
+	int nbytes;
+
+	fd2name(fd, buf, MAX_PATH);
+
+	if (fchmod(fd, mode) < 0) {
+		printf("fchmod(%s, 0%04o) failed: %m\n", buf, mode);
+		abort();
+	}
+
+	mfd_assert_mode(fd, mode);
+}
+
+static void mfd_fail_chmod(int fd, int mode)
+{
+	struct stat st;
+	char buf[MAX_PATH];
+	int nbytes;
+
+	fd2name(fd, buf, MAX_PATH);
+
+	if (fstat(fd, &st) < 0) {
+		printf("fstat(%s) failed: %m\n", buf);
+		abort();
+	}
+
+	if (fchmod(fd, mode) == 0) {
+		printf("fchmod(%s, 0%04o) didn't fail as expected\n",
+		       buf, mode);
+		abort();
+	}
+
+	/* verify that file mode bits did not change */
+	mfd_assert_mode(fd, st.st_mode & 07777);
+}
+
 static int idle_thread_fn(void *arg)
 {
 	sigset_t set;
@@ -880,6 +973,39 @@ static void test_seal_resize(void)
 	close(fd);
 }
 
+/*
+ * Test SEAL_EXEC
+ * Test that chmod() cannot change x bits after sealing
+ */
+static void test_seal_exec(void)
+{
+	int fd;
+
+	printf("%s SEAL-EXEC\n", memfd_str);
+
+	fd = mfd_assert_new("kern_memfd_seal_exec",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+	mfd_assert_mode(fd, 0777);
+
+	mfd_assert_chmod(fd, 0644);
+
+	mfd_assert_has_seals(fd, 0);
+	mfd_assert_add_seals(fd, F_SEAL_EXEC);
+	mfd_assert_has_seals(fd, F_SEAL_EXEC);
+
+	mfd_assert_chmod(fd, 0600);
+	mfd_fail_chmod(fd, 0777);
+	mfd_fail_chmod(fd, 0670);
+	mfd_fail_chmod(fd, 0605);
+	mfd_fail_chmod(fd, 0700);
+	mfd_fail_chmod(fd, 0100);
+	mfd_assert_chmod(fd, 0666);
+
+	close(fd);
+}
+
 /*
  * Test sharing via dup()
  * Test that seals are shared between dupped FDs and they're all equal.
@@ -1059,6 +1185,7 @@ int main(int argc, char **argv)
 	test_seal_shrink();
 	test_seal_grow();
 	test_seal_resize();
+	test_seal_exec();
 
 	test_share_dup("SHARE-DUP", "");
 	test_share_mmap("SHARE-MMAP", "");
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

[PATCH v5 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC

[jeffxu]

From: Jeff Xu <jeffxu@chromium.org>

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.

Signed-off-by: Jeff Xu <jeffxu@chromium.org>
Co-developed-by: Daniel Verkamp <dverkamp@chromium.org>
Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
Reported-by: kernel test robot <lkp@intel.com>
---
 include/linux/pid_namespace.h | 19 ++++++++++++++
 include/uapi/linux/memfd.h    |  4 +++
 kernel/pid_namespace.c        | 48 +++++++++++++++++++++++++++++++++++
 mm/memfd.c                    | 48 +++++++++++++++++++++++++++++++++--
 4 files changed, 117 insertions(+), 2 deletions(-)

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 07481bb87d4e..a4789a7b34a9 100644
--- 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 7a8a26751c23..273a4e15dfcf 100644
--- 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 f4f8cb0435b4..2b7563ddd22c 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -110,6 +110,11 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
 	ns->ucounts = ucounts;
 	ns->pid_allocated = PIDNS_ADDING;
 
+#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
+	ns->memfd_noexec_scope =
+		task_active_pid_ns(current)->memfd_noexec_scope;
+#endif
+
 	return ns;
 
 out_free_idr:
@@ -255,6 +260,45 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 	return;
 }
 
+#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
+static int pid_mfd_noexec_dointvec_minmax(struct ctl_table *table, int write,
+	void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct pid_namespace *ns = task_active_pid_ns(current);
+	struct ctl_table table_copy;
+
+	if (write && !capable(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, buffer, 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", }, { } };
+#endif
+
 #ifdef CONFIG_CHECKPOINT_RESTORE
 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 		void *buffer, size_t *lenp, loff_t *ppos)
@@ -455,6 +499,10 @@ static __init int pid_namespaces_init(void)
 #ifdef CONFIG_CHECKPOINT_RESTORE
 	register_sysctl_paths(kern_path, pid_ns_ctl_table);
 #endif
+
+#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
+	register_sysctl_paths(vm_path, pid_ns_ctl_table_vm);
+#endif
 	return 0;
 }
 
diff --git a/mm/memfd.c b/mm/memfd.c
index 4ebeab94aa74..ec70675a7069 100644
--- 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 +264,14 @@ 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];
+	struct pid_namespace *ns;
 	unsigned int *file_seals;
 	struct file *file;
 	int fd, error;
@@ -285,6 +288,39 @@ 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;
+
+		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_ratelimited(
+				"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_ratelimited(
+			"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;
 	}
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

[PATCH v5 4/6] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd

[jeffxu]

From: Jeff Xu <jeffxu@chromium.org>

In order to avoid WX mappings, add F_SEAL_WRITE when apply
F_SEAL_EXEC to an executable memfd, so W^X from start.

This implys application need to fill the content of the memfd first,
after F_SEAL_EXEC is applied, application can no longer modify the
content of the memfd.

Typically, application seals the memfd right after writing to it.
For example:
1. memfd_create(MFD_EXEC).
2. write() code to the memfd.
3. fcntl(F_ADD_SEALS, F_SEAL_EXEC) to convert the memfd to W^X.
4. call exec() on the memfd.

Signed-off-by: Jeff Xu <jeffxu@chromium.org>
---
 mm/memfd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/memfd.c b/mm/memfd.c
index ec70675a7069..92f0a5765f7c 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -222,6 +222,12 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 		}
 	}
 
+	/*
+	 * SEAL_EXEC implys SEAL_WRITE, making W^X from the start.
+	 */
+	if (seals & F_SEAL_EXEC && inode->i_mode & 0111)
+		seals |= F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE;
+
 	*file_seals |= seals;
 	error = 0;
 
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

[PATCH v5 5/6] selftests/memfd: add tests for MFD_NOEXEC_SEAL MFD_EXEC

[jeffxu]

From: Jeff Xu <jeffxu@chromium.org>

Tests to verify MFD_NOEXEC, MFD_EXEC and vm.memfd_noexec sysctl.

Signed-off-by: Jeff Xu <jeffxu@chromium.org>
Co-developed-by: Daniel Verkamp <dverkamp@chromium.org>
Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>

Change-Id: Idccec1141255ca948c849f4efc8ba5e97f78b6eb
---
 tools/testing/selftests/memfd/fuse_test.c  |   1 +
 tools/testing/selftests/memfd/memfd_test.c | 185 ++++++++++++++++++++-
 2 files changed, 181 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/memfd/fuse_test.c b/tools/testing/selftests/memfd/fuse_test.c
index be675002f918..93798c8c5d54 100644
--- a/tools/testing/selftests/memfd/fuse_test.c
+++ b/tools/testing/selftests/memfd/fuse_test.c
@@ -22,6 +22,7 @@
 #include <linux/falloc.h>
 #include <fcntl.h>
 #include <linux/memfd.h>
+#include <linux/types.h>
 #include <sched.h>
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index 1d7e7b36bbdd..7fc78ff62d40 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -32,10 +32,20 @@
 #define F_SEAL_EXEC	0x0020
 #endif
 
+#define F_WX_SEALS (F_SEAL_SHRINK | \
+		    F_SEAL_GROW | \
+		    F_SEAL_WRITE | \
+		    F_SEAL_FUTURE_WRITE | \
+		    F_SEAL_EXEC)
+
 #ifndef MAX_PATH
 #define MAX_PATH 256
 #endif
 
+#ifndef MFD_NOEXEC_SEAL
+#define MFD_NOEXEC_SEAL	0x0008U
+#endif
+
 /*
  * Default is not to test hugetlbfs
  */
@@ -86,6 +96,21 @@ static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags)
 	return fd;
 }
 
+static void sysctl_assert_write(const char *val)
+{
+	int fd = open("/proc/sys/vm/memfd_noexec", O_WRONLY | O_CLOEXEC);
+
+	if (fd < 0) {
+		printf("open sysctl failed\n");
+		abort();
+	}
+
+	if (write(fd, val, strlen(val)) < 0) {
+		printf("write sysctl failed\n");
+		abort();
+	}
+}
+
 static int mfd_assert_reopen_fd(int fd_in)
 {
 	int fd;
@@ -764,6 +789,9 @@ static void test_create(void)
 	mfd_fail_new("", ~0);
 	mfd_fail_new("", 0x80000000U);
 
+	/* verify EXEC and NOEXEC_SEAL can't both be set */
+	mfd_fail_new("", MFD_EXEC | MFD_NOEXEC_SEAL);
+
 	/* verify MFD_CLOEXEC is allowed */
 	fd = mfd_assert_new("", 0, MFD_CLOEXEC);
 	close(fd);
@@ -975,20 +1003,21 @@ static void test_seal_resize(void)
 
 /*
  * Test SEAL_EXEC
- * Test that chmod() cannot change x bits after sealing
+ * Test fd is created with exec and allow sealing.
+ * chmod() cannot change x bits after sealing.
  */
-static void test_seal_exec(void)
+static void test_exec_seal(void)
 {
 	int fd;
 
 	printf("%s SEAL-EXEC\n", memfd_str);
 
+	printf("%s	Apply SEAL_EXEC\n", memfd_str);
 	fd = mfd_assert_new("kern_memfd_seal_exec",
 			    mfd_def_size,
-			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_EXEC);
 
 	mfd_assert_mode(fd, 0777);
-
 	mfd_assert_chmod(fd, 0644);
 
 	mfd_assert_has_seals(fd, 0);
@@ -1002,10 +1031,152 @@ static void test_seal_exec(void)
 	mfd_fail_chmod(fd, 0700);
 	mfd_fail_chmod(fd, 0100);
 	mfd_assert_chmod(fd, 0666);
+	mfd_assert_write(fd);
+	close(fd);
+
+	printf("%s	Apply ALL_SEALS\n", memfd_str);
+	fd = mfd_assert_new("kern_memfd_seal_exec",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_EXEC);
+
+	mfd_assert_mode(fd, 0777);
+	mfd_assert_chmod(fd, 0700);
+
+	mfd_assert_has_seals(fd, 0);
+	mfd_assert_add_seals(fd, F_SEAL_EXEC);
+	mfd_assert_has_seals(fd, F_WX_SEALS);
 
+	mfd_fail_chmod(fd, 0711);
+	mfd_fail_chmod(fd, 0600);
+	mfd_fail_write(fd);
 	close(fd);
 }
 
+/*
+ * Test EXEC_NO_SEAL
+ * Test fd is created with exec and not allow sealing.
+ */
+static void test_exec_no_seal(void)
+{
+	int fd;
+
+	printf("%s EXEC_NO_SEAL\n", memfd_str);
+
+	/* Create with EXEC but without ALLOW_SEALING */
+	fd = mfd_assert_new("kern_memfd_exec_no_sealing",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_EXEC);
+	mfd_assert_mode(fd, 0777);
+	mfd_assert_has_seals(fd, F_SEAL_SEAL);
+	mfd_assert_chmod(fd, 0666);
+	close(fd);
+}
+
+/*
+ * Test memfd_create with MFD_NOEXEC flag
+ */
+static void test_noexec_seal(void)
+{
+	int fd;
+
+	printf("%s NOEXEC_SEAL\n", memfd_str);
+
+	/* Create with NOEXEC and ALLOW_SEALING */
+	fd = mfd_assert_new("kern_memfd_noexec",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_NOEXEC_SEAL);
+	mfd_assert_mode(fd, 0666);
+	mfd_assert_has_seals(fd, F_SEAL_EXEC);
+	mfd_fail_chmod(fd, 0777);
+	close(fd);
+
+	/* Create with NOEXEC but without ALLOW_SEALING */
+	fd = mfd_assert_new("kern_memfd_noexec",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_NOEXEC_SEAL);
+	mfd_assert_mode(fd, 0666);
+	mfd_assert_has_seals(fd, F_SEAL_EXEC);
+	mfd_fail_chmod(fd, 0777);
+	close(fd);
+}
+
+static void test_sysctl_child(void)
+{
+	int fd, pid, ret;
+
+	printf("%s sysctl 0\n", memfd_str);
+	sysctl_assert_write("0");
+	fd = mfd_assert_new("kern_memfd_sysctl_0",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+	mfd_assert_mode(fd, 0777);
+	mfd_assert_has_seals(fd, 0);
+	mfd_assert_chmod(fd, 0644);
+	close(fd);
+
+	printf("%s sysctl 1\n", memfd_str);
+	sysctl_assert_write("1");
+	fd = mfd_assert_new("kern_memfd_sysctl_1",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+	mfd_assert_mode(fd, 0666);
+	mfd_assert_has_seals(fd, F_SEAL_EXEC);
+	mfd_fail_chmod(fd, 0777);
+	close(fd);
+
+	printf("%s sysctl 2\n", memfd_str);
+	sysctl_assert_write("2");
+	mfd_fail_new("kern_memfd_sysctl_2",
+		MFD_CLOEXEC | MFD_ALLOW_SEALING);
+}
+
+static int newpid_thread_fn(void *arg)
+{
+	test_sysctl_child();
+	return 0;
+}
+
+static pid_t spawn_newpid_thread(unsigned int flags)
+{
+	uint8_t *stack;
+	pid_t pid;
+
+	stack = malloc(STACK_SIZE);
+	if (!stack) {
+		printf("malloc(STACK_SIZE) failed: %m\n");
+		abort();
+	}
+
+	pid = clone(newpid_thread_fn,
+		    stack + STACK_SIZE,
+		    SIGCHLD | flags,
+		    NULL);
+	if (pid < 0) {
+		printf("clone() failed: %m\n");
+		abort();
+	}
+
+	return pid;
+}
+
+static void join_newpid_thread(pid_t pid)
+{
+	waitpid(pid, NULL, 0);
+}
+
+/*
+ * Test sysctl
+ * A very basic sealing test to see whether setting/retrieving seals works.
+ */
+static void test_sysctl(void)
+{
+	int pid = spawn_newpid_thread(CLONE_NEWPID);
+
+	join_newpid_thread(pid);
+}
+
 /*
  * Test sharing via dup()
  * Test that seals are shared between dupped FDs and they're all equal.
@@ -1179,13 +1350,15 @@ int main(int argc, char **argv)
 
 	test_create();
 	test_basic();
+	test_exec_seal();
+	test_exec_no_seal();
+	test_noexec_seal();
 
 	test_seal_write();
 	test_seal_future_write();
 	test_seal_shrink();
 	test_seal_grow();
 	test_seal_resize();
-	test_seal_exec();
 
 	test_share_dup("SHARE-DUP", "");
 	test_share_mmap("SHARE-MMAP", "");
@@ -1201,6 +1374,8 @@ int main(int argc, char **argv)
 	test_share_fork("SHARE-FORK", SHARED_FT_STR);
 	join_idle_thread(pid);
 
+	test_sysctl();
+
 	printf("memfd: DONE\n");
 
 	return 0;
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

[PATCH v5 6/6] mm/memfd: security hook for memfd_create

[jeffxu]

From: Jeff Xu <jeffxu@chromium.org>

The new security_memfd_create allows lsm to check flags of
memfd_create.

The security by default system (such as chromeos) can use this
to implement system wide lsm to allow only non-executable memfd
being created.

Signed-off-by: Jeff Xu <jeffxu@chromium.org>
Reported-by: kernel test robot <lkp@intel.com>
---
 include/linux/lsm_hook_defs.h |  1 +
 include/linux/lsm_hooks.h     |  4 ++++
 include/linux/security.h      |  6 ++++++
 mm/memfd.c                    |  5 +++++
 security/security.c           | 13 +++++++++++++
 5 files changed, 29 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index ec119da1d89b..fd40840927c8 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -164,6 +164,7 @@ LSM_HOOK(int, 0, file_alloc_security, struct file *file)
 LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file)
 LSM_HOOK(int, 0, file_ioctl, struct file *file, unsigned int cmd,
 	 unsigned long arg)
+LSM_HOOK(int, 0, memfd_create, char *name, unsigned int flags)
 LSM_HOOK(int, 0, mmap_addr, unsigned long addr)
 LSM_HOOK(int, 0, mmap_file, struct file *file, unsigned long reqprot,
 	 unsigned long prot, unsigned long flags)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 4ec80b96c22e..5a18a6552278 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -543,6 +543,10 @@
  *	simple integer value.  When @arg represents a user space pointer, it
  *	should never be used by the security module.
  *	Return 0 if permission is granted.
+ * @memfd_create:
+ *	@name is the name of memfd file.
+ *	@flags is the flags used in memfd_create.
+ *	Return 0 if permission is granted.
  * @mmap_addr :
  *	Check permissions for a mmap operation at @addr.
  *	@addr contains virtual address that will be used for the operation.
diff --git a/include/linux/security.h b/include/linux/security.h
index ca1b7109c0db..5b87a780822a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -384,6 +384,7 @@ int security_file_permission(struct file *file, int mask);
 int security_file_alloc(struct file *file);
 void security_file_free(struct file *file);
 int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
+int security_memfd_create(char *name, unsigned int flags);
 int security_mmap_file(struct file *file, unsigned long prot,
 			unsigned long flags);
 int security_mmap_addr(unsigned long addr);
@@ -963,6 +964,11 @@ static inline int security_file_ioctl(struct file *file, unsigned int cmd,
 	return 0;
 }
 
+static inline int security_memfd_create(char *name, unsigned int flags)
+{
+	return 0;
+}
+
 static inline int security_mmap_file(struct file *file, unsigned long prot,
 				     unsigned long flags)
 {
diff --git a/mm/memfd.c b/mm/memfd.c
index 92f0a5765f7c..f04ed5f0474f 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -356,6 +356,11 @@ SYSCALL_DEFINE2(memfd_create,
 		goto err_name;
 	}
 
+	/* security hook for memfd_create */
+	error = security_memfd_create(name, flags);
+	if (error)
+		return error;
+
 	if (flags & MFD_HUGETLB) {
 		file = hugetlb_file_setup(name, 0, VM_NORESERVE,
 					HUGETLB_ANONHUGE_INODE,
diff --git a/security/security.c b/security/security.c
index 79d82cb6e469..5c018e080923 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1010,6 +1010,19 @@ int security_sb_clone_mnt_opts(const struct super_block *oldsb,
 }
 EXPORT_SYMBOL(security_sb_clone_mnt_opts);
 
+int security_add_mnt_opt(const char *option, const char *val, int len,
+			 void **mnt_opts)
+{
+	return call_int_hook(sb_add_mnt_opt, -EINVAL,
+					option, val, len, mnt_opts);
+}
+EXPORT_SYMBOL(security_add_mnt_opt);
+
+int security_memfd_create(char *name, unsigned int flags)
+{
+	return call_int_hook(memfd_create, 0, name, flags);
+}
+
 int security_move_mount(const struct path *from_path, const struct path *to_path)
 {
 	return call_int_hook(move_mount, 0, from_path, to_path);
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

Re: [PATCH v5 5/6] selftests/memfd: add tests for MFD_NOEXEC_SEAL MFD_EXEC

[Greg KH]

On Tue, Dec 06, 2022 at 03:23:57PM +0000, jeffxu@chromium.org wrote:
> From: Jeff Xu <jeffxu@chromium.org>
> 
> Tests to verify MFD_NOEXEC, MFD_EXEC and vm.memfd_noexec sysctl.
> 
> Signed-off-by: Jeff Xu <jeffxu@chromium.org>
> Co-developed-by: Daniel Verkamp <dverkamp@chromium.org>
> Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
> 
> Change-Id: Idccec1141255ca948c849f4efc8ba5e97f78b6eb

Always use checkpatch.pl on your patches so you don't get grumpy
maintainers telling you to run checkpatch.pl on your patches...

thanks,

greg k-h

Re: [PATCH v5 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC

[Greg KH]

On Tue, Dec 06, 2022 at 03:23:55PM +0000, jeffxu@chromium.org wrote:
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -110,6 +110,11 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
>  	ns->ucounts = ucounts;
>  	ns->pid_allocated = PIDNS_ADDING;
>  
> +#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> +	ns->memfd_noexec_scope =
> +		task_active_pid_ns(current)->memfd_noexec_scope;
> +#endif

.c files should never have #if in them.  Can't you put this in a .h file
properly so that this does not get really messy over time?



> +
>  	return ns;
>  
>  out_free_idr:
> @@ -255,6 +260,45 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
>  	return;
>  }
>  
> +#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)

Same here.

thanks,

greg k-h

Re: [PATCH v5 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC

[Jeff Xu]

On Tue, Dec 6, 2022 at 8:04 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, Dec 06, 2022 at 03:23:55PM +0000, jeffxu@chromium.org wrote:
> > --- a/kernel/pid_namespace.c
> > +++ b/kernel/pid_namespace.c
> > @@ -110,6 +110,11 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> >       ns->ucounts = ucounts;
> >       ns->pid_allocated = PIDNS_ADDING;
> >
> > +#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> > +     ns->memfd_noexec_scope =
> > +             task_active_pid_ns(current)->memfd_noexec_scope;
> > +#endif
>
> .c files should never have #if in them.  Can't you put this in a .h file
> properly so that this does not get really messy over time?
>
>
Thanks for reviewing.
It seems to me that checking for CONFIG_XXX is  common in c code in
kernel/ path.
Do you have a sample code pattern (link/function) that I can follow?

Thanks
Jeff

>
> > +
> >       return ns;
> >
> >  out_free_idr:
> > @@ -255,6 +260,45 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
> >       return;
> >  }
> >
> > +#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
>
> Same here.
>
> thanks,
>
> greg k-h

Re: [PATCH v5 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC

[Greg KH]

On Tue, Dec 06, 2022 at 08:26:30AM -0800, Jeff Xu wrote:
> On Tue, Dec 6, 2022 at 8:04 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Tue, Dec 06, 2022 at 03:23:55PM +0000, jeffxu@chromium.org wrote:
> > > --- a/kernel/pid_namespace.c
> > > +++ b/kernel/pid_namespace.c
> > > @@ -110,6 +110,11 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> > >       ns->ucounts = ucounts;
> > >       ns->pid_allocated = PIDNS_ADDING;
> > >
> > > +#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> > > +     ns->memfd_noexec_scope =
> > > +             task_active_pid_ns(current)->memfd_noexec_scope;
> > > +#endif
> >
> > .c files should never have #if in them.  Can't you put this in a .h file
> > properly so that this does not get really messy over time?
> >
> >
> Thanks for reviewing.
> It seems to me that checking for CONFIG_XXX is  common in c code in
> kernel/ path.

Maybe, but please don't make it any worse if at all possible.  It's
tough to maintain code like that.

> Do you have a sample code pattern (link/function) that I can follow?

Any of the zillions of #if statements in .h files :)

thanks,

greg k-h

Re: [PATCH v5 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC

[Jeff Xu]

On Tue, Dec 6, 2022 at 8:35 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, Dec 06, 2022 at 08:26:30AM -0800, Jeff Xu wrote:
> > On Tue, Dec 6, 2022 at 8:04 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > >
> > > On Tue, Dec 06, 2022 at 03:23:55PM +0000, jeffxu@chromium.org wrote:
> > > > --- a/kernel/pid_namespace.c
> > > > +++ b/kernel/pid_namespace.c
> > > > @@ -110,6 +110,11 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> > > >       ns->ucounts = ucounts;
> > > >       ns->pid_allocated = PIDNS_ADDING;
> > > >
> > > > +#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> > > > +     ns->memfd_noexec_scope =
> > > > +             task_active_pid_ns(current)->memfd_noexec_scope;
> > > > +#endif
> > >
> > > .c files should never have #if in them.  Can't you put this in a .h file
> > > properly so that this does not get really messy over time?
> > >
> > >
> > Thanks for reviewing.
> > It seems to me that checking for CONFIG_XXX is  common in c code in
> > kernel/ path.
>
> Maybe, but please don't make it any worse if at all possible.  It's
> tough to maintain code like that.
>
> > Do you have a sample code pattern (link/function) that I can follow?
>
> Any of the zillions of #if statements in .h files :)
>
Thanks.
I will take the approach of having real/stub implementation in the h
file, and the c file  using it without a compile flag.
Please kindly let me know if this is not right.

Thanks
Jeff

> thanks,
>
> greg k-h

Re: [PATCH v5 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC

[Kees Cook]

On Tue, Dec 06, 2022 at 09:48:55AM -0800, Jeff Xu wrote:
> On Tue, Dec 6, 2022 at 8:35 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Tue, Dec 06, 2022 at 08:26:30AM -0800, Jeff Xu wrote:
> > > On Tue, Dec 6, 2022 at 8:04 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > On Tue, Dec 06, 2022 at 03:23:55PM +0000, jeffxu@chromium.org wrote:
> > > > > --- a/kernel/pid_namespace.c
> > > > > +++ b/kernel/pid_namespace.c
> > > > > @@ -110,6 +110,11 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> > > > >       ns->ucounts = ucounts;
> > > > >       ns->pid_allocated = PIDNS_ADDING;
> > > > >
> > > > > +#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> > > > > +     ns->memfd_noexec_scope =
> > > > > +             task_active_pid_ns(current)->memfd_noexec_scope;
> > > > > +#endif
> > > >
> > > > .c files should never have #if in them.  Can't you put this in a .h file
> > > > properly so that this does not get really messy over time?
> > > >
> > > >
> > > Thanks for reviewing.
> > > It seems to me that checking for CONFIG_XXX is  common in c code in
> > > kernel/ path.
> >
> > Maybe, but please don't make it any worse if at all possible.  It's
> > tough to maintain code like that.
> >
> > > Do you have a sample code pattern (link/function) that I can follow?
> >
> > Any of the zillions of #if statements in .h files :)
> >
> Thanks.
> I will take the approach of having real/stub implementation in the h
> file, and the c file  using it without a compile flag.
> Please kindly let me know if this is not right.

Right; for example:

in .h:

#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
static inline void ns_copy_memfd_scope(... dst, ... src) {
	dst->memfd_noexec_scope = src->memfd_noexec_scope;
}
#else
static inline void ns_set_memfd_scope(... ns, ... scope) { }
#endif


in .c:

	ns_copy_memfd_scope(ns, task_active_pid_ns(current));


-- 
Kees Cook