diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 786728143205218e135fab4b780b7b036b64c595..5b5c9189c507dd4382bff257fb3587ce18e4e7f6 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -402,7 +402,8 @@
388 i386 move_mount sys_move_mount __ia32_sys_move_mount
389 i386 fsopen sys_fsopen __ia32_sys_fsopen
390 i386 fsconfig sys_fsconfig __ia32_sys_fsconfig
-# don't use numbers 391 through 392, add new calls at the end
+391 i386 fsmount sys_fsmount __ia32_sys_fsmount
+# don't use number 392, add new calls at the end
393 i386 semget sys_semget __ia32_sys_semget
394 i386 semctl sys_semctl __ia32_compat_sys_semctl
395 i386 shmget sys_shmget __ia32_sys_shmget
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 7039a809d37d10562a53bebdf395e66b59c6d394..984ad594bb2bb7fd0fad5931eb0d383861a0e374 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -347,6 +347,7 @@
336 common move_mount __x64_sys_move_mount
337 common fsopen __x64_sys_fsopen
338 common fsconfig __x64_sys_fsconfig
+339 common fsmount __x64_sys_fsmount
# don't use numbers 387 through 423, add new calls after the last
# 'common' entry
424 common pidfd_send_signal __x64_sys_pidfd_send_signal
diff --git a/fs/namespace.c b/fs/namespace.c
index 1e72d19fa4f85a2b3c7a643d32a7d721c1623101..3357c3d65475a722c345ace8e95552055dc35480 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3334,9 +3334,149 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
}
/*
- * Move a mount from one place to another.
- * In combination with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be
- * used to copy a mount subtree.
+ * Create a kernel mount representation for a new, prepared superblock
+ * (specified by fs_fd) and attach to an open_tree-like file descriptor.
+ */
+SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
+ unsigned int, attr_flags)
+{
+ struct mnt_namespace *ns;
+ struct fs_context *fc;
+ struct file *file;
+ struct path newmount;
+ struct mount *mnt;
+ struct fd f;
+ unsigned int mnt_flags = 0;
+ long ret;
+
+ if (!may_mount())
+ return -EPERM;
+
+ if ((flags & ~(FSMOUNT_CLOEXEC)) != 0)
+ return -EINVAL;
+
+ if (attr_flags & ~(MOUNT_ATTR_RDONLY |
+ MOUNT_ATTR_NOSUID |
+ MOUNT_ATTR_NODEV |
+ MOUNT_ATTR_NOEXEC |
+ MOUNT_ATTR__ATIME |
+ MOUNT_ATTR_NODIRATIME))
+ return -EINVAL;
+
+ if (attr_flags & MOUNT_ATTR_RDONLY)
+ mnt_flags |= MNT_READONLY;
+ if (attr_flags & MOUNT_ATTR_NOSUID)
+ mnt_flags |= MNT_NOSUID;
+ if (attr_flags & MOUNT_ATTR_NODEV)
+ mnt_flags |= MNT_NODEV;
+ if (attr_flags & MOUNT_ATTR_NOEXEC)
+ mnt_flags |= MNT_NOEXEC;
+ if (attr_flags & MOUNT_ATTR_NODIRATIME)
+ mnt_flags |= MNT_NODIRATIME;
+
+ switch (attr_flags & MOUNT_ATTR__ATIME) {
+ case MOUNT_ATTR_STRICTATIME:
+ break;
+ case MOUNT_ATTR_NOATIME:
+ mnt_flags |= MNT_NOATIME;
+ break;
+ case MOUNT_ATTR_RELATIME:
+ mnt_flags |= MNT_RELATIME;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ f = fdget(fs_fd);
+ if (!f.file)
+ return -EBADF;
+
+ ret = -EINVAL;
+ if (f.file->f_op != &fscontext_fops)
+ goto err_fsfd;
+
+ fc = f.file->private_data;
+
+ ret = mutex_lock_interruptible(&fc->uapi_mutex);
+ if (ret < 0)
+ goto err_fsfd;
+
+ /* There must be a valid superblock or we can't mount it */
+ ret = -EINVAL;
+ if (!fc->root)
+ goto err_unlock;
+
+ ret = -EPERM;
+ if (mount_too_revealing(fc->root->d_sb, &mnt_flags)) {
+ pr_warn("VFS: Mount too revealing\n");
+ goto err_unlock;
+ }
+
+ ret = -EBUSY;
+ if (fc->phase != FS_CONTEXT_AWAITING_MOUNT)
+ goto err_unlock;
+
+ ret = -EPERM;
+ if ((fc->sb_flags & SB_MANDLOCK) && !may_mandlock())
+ goto err_unlock;
+
+ newmount.mnt = vfs_create_mount(fc);
+ if (IS_ERR(newmount.mnt)) {
+ ret = PTR_ERR(newmount.mnt);
+ goto err_unlock;
+ }
+ newmount.dentry = dget(fc->root);
+ newmount.mnt->mnt_flags = mnt_flags;
+
+ /* We've done the mount bit - now move the file context into more or
+ * less the same state as if we'd done an fspick(). We don't want to
+ * do any memory allocation or anything like that at this point as we
+ * don't want to have to handle any errors incurred.
+ */
+ vfs_clean_context(fc);
+
+ ns = alloc_mnt_ns(current->nsproxy->mnt_ns->user_ns, true);
+ if (IS_ERR(ns)) {
+ ret = PTR_ERR(ns);
+ goto err_path;
+ }
+ mnt = real_mount(newmount.mnt);
+ mnt->mnt_ns = ns;
+ ns->root = mnt;
+ ns->mounts = 1;
+ list_add(&mnt->mnt_list, &ns->list);
+
+ /* Attach to an apparent O_PATH fd with a note that we need to unmount
+ * it, not just simply put it.
+ */
+ file = dentry_open(&newmount, O_PATH, fc->cred);
+ if (IS_ERR(file)) {
+ dissolve_on_fput(newmount.mnt);
+ ret = PTR_ERR(file);
+ goto err_path;
+ }
+ file->f_mode |= FMODE_NEED_UNMOUNT;
+
+ ret = get_unused_fd_flags((flags & FSMOUNT_CLOEXEC) ? O_CLOEXEC : 0);
+ if (ret >= 0)
+ fd_install(ret, file);
+ else
+ fput(file);
+
+err_path:
+ path_put(&newmount);
+err_unlock:
+ mutex_unlock(&fc->uapi_mutex);
+err_fsfd:
+ fdput(f);
+ return ret;
+}
+
+/*
+ * Move a mount from one place to another. In combination with
+ * fsopen()/fsmount() this is used to install a new mount and in combination
+ * with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be used to copy
+ * a mount subtree.
*
* Note the flags value is a combination of MOVE_MOUNT_* flags.
*/
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 925f9dfc356b18bf0477a6441a15679727e9cc25..0e697f595278948d39fd3f0ebac27b3ea3cd7934 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -992,6 +992,7 @@ asmlinkage long sys_move_mount(int from_dfd, const char __user *from_path,
asmlinkage long sys_fsopen(const char __user *fs_name, unsigned int flags);
asmlinkage long sys_fsconfig(int fs_fd, unsigned int cmd, const char __user *key,
const void __user *value, int aux);
+asmlinkage long sys_fsmount(int fs_fd, unsigned int flags, unsigned int ms_flags);
asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
siginfo_t __user *info,
unsigned int flags);
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index 4b90ba9d1770d3d71e0045a668282b89ab141da1..3888d3b91dc5035f86f3575e7760f387db1aa299 100644
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -91,4 +91,22 @@ enum fsconfig_command {
FSCONFIG_CMD_RECONFIGURE = 7, /* Invoke superblock reconfiguration */
};
+/*
+ * fsmount() flags.
+ */
+#define FSMOUNT_CLOEXEC 0x00000001
+
+/*
+ * Mount attributes.
+ */
+#define MOUNT_ATTR_RDONLY 0x00000001 /* Mount read-only */
+#define MOUNT_ATTR_NOSUID 0x00000002 /* Ignore suid and sgid bits */
+#define MOUNT_ATTR_NODEV 0x00000004 /* Disallow access to device special files */
+#define MOUNT_ATTR_NOEXEC 0x00000008 /* Disallow program execution */
+#define MOUNT_ATTR__ATIME 0x00000070 /* Setting on how atime should be updated */
+#define MOUNT_ATTR_RELATIME 0x00000000 /* - Update atime relative to mtime/ctime. */
+#define MOUNT_ATTR_NOATIME 0x00000010 /* - Do not update access times. */
+#define MOUNT_ATTR_STRICTATIME 0x00000020 /* - Always perform atime updates */
+#define MOUNT_ATTR_NODIRATIME 0x00000080 /* Do not update directory access times */
+
#endif /* _UAPI_LINUX_MOUNT_H */