// SPDX-License-Identifier: GPL-2.0-only

  /*

   * binfmt_misc.c

   *

   * Copyright (C) 1997 Richard Günther

   *

   * binfmt_misc detects binaries via a magic or filename extension and invokes

   * a specified wrapper. See Documentation/admin-guide/binfmt-misc.rst for more details.

   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #include <linux/kernel.h>

  #include <linux/module.h>
  #include <linux/init.h>

  #include <linux/sched/mm.h>

  #include <linux/magic.h>

  #include <linux/binfmts.h>
  #include <linux/slab.h>
  #include <linux/ctype.h>

  #include <linux/string_helpers.h>

  #include <linux/file.h>
  #include <linux/pagemap.h>
  #include <linux/namei.h>
  #include <linux/mount.h>

  #include <linux/fs_context.h>

  #include <linux/syscalls.h>

  #include <linux/fs.h>

  #include <linux/uaccess.h>

  #include "internal.h"

  #ifdef DEBUG
  # define USE_DEBUG 1
  #else
  # define USE_DEBUG 0
  #endif

  
  enum {
  	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  };
  
  static LIST_HEAD(entries);
  static int enabled = 1;
  
  enum {Enabled, Magic};

  #define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
  #define MISC_FMT_OPEN_BINARY (1 << 30)
  #define MISC_FMT_CREDENTIALS (1 << 29)

  #define MISC_FMT_OPEN_FILE (1 << 28)

  
  typedef struct {
  	struct list_head list;
  	unsigned long flags;		/* type, status, etc. */
  	int offset;			/* offset of magic */
  	int size;			/* size of magic/mask */
  	char *magic;			/* magic or filename extension */
  	char *mask;			/* mask, NULL for exact match */

  	const char *interpreter;	/* filename of interpreter */

  	char *name;
  	struct dentry *dentry;

  	struct file *interp_file;

  } Node;
  
  static DEFINE_RWLOCK(entries_lock);

  static struct file_system_type bm_fs_type;

  static struct vfsmount *bm_mnt;
  static int entry_count;

  /*
   * Max length of the register string.  Determined by:
   *  - 7 delimiters
   *  - name:   ~50 bytes
   *  - type:   1 byte
   *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
   *  - magic:  128 bytes (512 in escaped form)
   *  - mask:   128 bytes (512 in escaped form)
   *  - interp: ~50 bytes
   *  - flags:  5 bytes
   * Round that up a bit, and then back off to hold the internal data
   * (like struct Node).
   */
  #define MAX_REGISTER_LENGTH 1920
  
  /*

   * Check if we support the binfmt
   * if we do, return the node, else NULL
   * locking is done in load_misc_binary
   */
  static Node *check_file(struct linux_binprm *bprm)
  {
  	char *p = strrchr(bprm->interp, '.');
  	struct list_head *l;

  	/* Walk all the registered handlers. */

  	list_for_each(l, &entries) {
  		Node *e = list_entry(l, Node, list);
  		char *s;
  		int j;

  		/* Make sure this one is currently enabled. */

  		if (!test_bit(Enabled, &e->flags))
  			continue;

  		/* Do matching based on extension if applicable. */

  		if (!test_bit(Magic, &e->flags)) {
  			if (p && !strcmp(e->magic, p + 1))
  				return e;
  			continue;
  		}

  		/* Do matching based on magic & mask. */

  		s = bprm->buf + e->offset;
  		if (e->mask) {
  			for (j = 0; j < e->size; j++)
  				if ((*s++ ^ e->magic[j]) & e->mask[j])
  					break;
  		} else {
  			for (j = 0; j < e->size; j++)
  				if ((*s++ ^ e->magic[j]))
  					break;
  		}
  		if (j == e->size)
  			return e;
  	}
  	return NULL;
  }
  
  /*
   * the loader itself
   */

  static int load_misc_binary(struct linux_binprm *bprm)

  {
  	Node *fmt;

  	struct file *interp_file = NULL;

  	int retval;

  
  	retval = -ENOEXEC;
  	if (!enabled)

  		return retval;

  
  	/* to keep locking time low, we copy the interpreter string */
  	read_lock(&entries_lock);
  	fmt = check_file(bprm);

  	if (fmt)

  		dget(fmt->dentry);

  	read_unlock(&entries_lock);
  	if (!fmt)

  		return retval;

  	/* Need to be able to load the file after exec */

  	retval = -ENOENT;

  	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)

  		goto ret;

  	if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {

  		retval = remove_arg_zero(bprm);
  		if (retval)

  			goto ret;

  	}

  	if (fmt->flags & MISC_FMT_OPEN_BINARY)

  		bprm->have_execfd = 1;

  	/* make argv[1] be the path to the binary */

  	retval = copy_string_kernel(bprm->interp, bprm);

  	if (retval < 0)

  		goto ret;

  	bprm->argc++;
  
  	/* add the interp as argv[0] */

  	retval = copy_string_kernel(fmt->interpreter, bprm);

  	if (retval < 0)

  		goto ret;

  	bprm->argc++;

  	/* Update interp in case binfmt_script needs it. */

  	retval = bprm_change_interp(fmt->interpreter, bprm);

  	if (retval < 0)

  		goto ret;

  	if (fmt->flags & MISC_FMT_OPEN_FILE) {

  		interp_file = file_clone_open(fmt->interp_file);

  		if (!IS_ERR(interp_file))
  			deny_write_access(interp_file);
  	} else {

  		interp_file = open_exec(fmt->interpreter);

  	}

  	retval = PTR_ERR(interp_file);
  	if (IS_ERR(interp_file))

  		goto ret;

  	bprm->interpreter = interp_file;

  	if (fmt->flags & MISC_FMT_CREDENTIALS)

  		bprm->execfd_creds = 1;

  	retval = 0;

  ret:

  	dput(fmt->dentry);

  	return retval;

  }
  
  /* Command parsers */
  
  /*
   * parses and copies one argument enclosed in del from *sp to *dp,
   * recognising the \x special.
   * returns pointer to the copied argument or NULL in case of an
   * error (and sets err) or null argument length.
   */
  static char *scanarg(char *s, char del)
  {
  	char c;
  
  	while ((c = *s++) != del) {
  		if (c == '\\' && *s == 'x') {
  			s++;
  			if (!isxdigit(*s++))
  				return NULL;
  			if (!isxdigit(*s++))
  				return NULL;
  		}
  	}

  	s[-1] ='\0';

  	return s;
  }

  static char *check_special_flags(char *sfs, Node *e)

  {

  	char *p = sfs;

  	int cont = 1;
  
  	/* special flags */
  	while (cont) {
  		switch (*p) {

  		case 'P':
  			pr_debug("register: flag: P (preserve argv0)
  ");
  			p++;
  			e->flags |= MISC_FMT_PRESERVE_ARGV0;
  			break;
  		case 'O':
  			pr_debug("register: flag: O (open binary)
  ");
  			p++;
  			e->flags |= MISC_FMT_OPEN_BINARY;
  			break;
  		case 'C':
  			pr_debug("register: flag: C (preserve creds)
  ");
  			p++;
  			/* this flags also implies the
  			   open-binary flag */
  			e->flags |= (MISC_FMT_CREDENTIALS |
  					MISC_FMT_OPEN_BINARY);
  			break;

  		case 'F':
  			pr_debug("register: flag: F: open interpreter file now
  ");
  			p++;
  			e->flags |= MISC_FMT_OPEN_FILE;
  			break;

  		default:
  			cont = 0;

  		}
  	}
  
  	return p;
  }

  /*
   * This registers a new binary format, it recognises the syntax
   * ':name:type:offset:magic:mask:interpreter:flags'
   * where the ':' is the IFS, that can be chosen with the first char
   */
  static Node *create_entry(const char __user *buffer, size_t count)
  {
  	Node *e;
  	int memsize, err;
  	char *buf, *p;
  	char del;

  	pr_debug("register: received %zu bytes
  ", count);

  	/* some sanity checks */
  	err = -EINVAL;

  	if ((count < 11) || (count > MAX_REGISTER_LENGTH))

  		goto out;
  
  	err = -ENOMEM;
  	memsize = sizeof(Node) + count + 8;

  	e = kmalloc(memsize, GFP_KERNEL);

  	if (!e)
  		goto out;
  
  	p = buf = (char *)e + sizeof(Node);
  
  	memset(e, 0, sizeof(Node));
  	if (copy_from_user(buf, buffer, count))

  		goto efault;

  
  	del = *p++;	/* delimeter */

  	pr_debug("register: delim: %#x {%c}
  ", del, del);
  
  	/* Pad the buffer with the delim to simplify parsing below. */

  	memset(buf + count, del, 8);

  	/* Parse the 'name' field. */

  	e->name = p;
  	p = strchr(p, del);
  	if (!p)

  		goto einval;

  	*p++ = '\0';
  	if (!e->name[0] ||
  	    !strcmp(e->name, ".") ||
  	    !strcmp(e->name, "..") ||
  	    strchr(e->name, '/'))

  		goto einval;

  
  	pr_debug("register: name: {%s}
  ", e->name);
  
  	/* Parse the 'type' field. */

  	switch (*p++) {

  	case 'E':
  		pr_debug("register: type: E (extension)
  ");
  		e->flags = 1 << Enabled;
  		break;
  	case 'M':
  		pr_debug("register: type: M (magic)
  ");
  		e->flags = (1 << Enabled) | (1 << Magic);
  		break;
  	default:

  		goto einval;

  	}
  	if (*p++ != del)

  		goto einval;

  	if (test_bit(Magic, &e->flags)) {

  		/* Handle the 'M' (magic) format. */
  		char *s;
  
  		/* Parse the 'offset' field. */
  		s = strchr(p, del);

  		if (!s)

  			goto einval;

  		*s = '\0';
  		if (p != s) {
  			int r = kstrtoint(p, 10, &e->offset);
  			if (r != 0 || e->offset < 0)
  				goto einval;
  		}
  		p = s;

  		if (*p++)

  			goto einval;

  		pr_debug("register: offset: %#x
  ", e->offset);
  
  		/* Parse the 'magic' field. */

  		e->magic = p;
  		p = scanarg(p, del);
  		if (!p)

  			goto einval;

  		if (!e->magic[0])

  			goto einval;

  		if (USE_DEBUG)
  			print_hex_dump_bytes(
  				KBUILD_MODNAME ": register: magic[raw]: ",
  				DUMP_PREFIX_NONE, e->magic, p - e->magic);
  
  		/* Parse the 'mask' field. */

  		e->mask = p;
  		p = scanarg(p, del);
  		if (!p)

  			goto einval;

  		if (!e->mask[0]) {

  			e->mask = NULL;

  			pr_debug("register:  mask[raw]: none
  ");
  		} else if (USE_DEBUG)
  			print_hex_dump_bytes(
  				KBUILD_MODNAME ": register:  mask[raw]: ",
  				DUMP_PREFIX_NONE, e->mask, p - e->mask);
  
  		/*
  		 * Decode the magic & mask fields.
  		 * Note: while we might have accepted embedded NUL bytes from
  		 * above, the unescape helpers here will stop at the first one
  		 * it encounters.
  		 */

  		e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
  		if (e->mask &&
  		    string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)

  			goto einval;

  		if (e->size > BINPRM_BUF_SIZE ||
  		    BINPRM_BUF_SIZE - e->size < e->offset)

  			goto einval;

  		pr_debug("register: magic/mask length: %i
  ", e->size);
  		if (USE_DEBUG) {
  			print_hex_dump_bytes(
  				KBUILD_MODNAME ": register: magic[decoded]: ",
  				DUMP_PREFIX_NONE, e->magic, e->size);
  
  			if (e->mask) {
  				int i;

  				char *masked = kmalloc(e->size, GFP_KERNEL);

  
  				print_hex_dump_bytes(
  					KBUILD_MODNAME ": register:  mask[decoded]: ",
  					DUMP_PREFIX_NONE, e->mask, e->size);
  
  				if (masked) {
  					for (i = 0; i < e->size; ++i)
  						masked[i] = e->magic[i] & e->mask[i];
  					print_hex_dump_bytes(
  						KBUILD_MODNAME ": register:  magic[masked]: ",
  						DUMP_PREFIX_NONE, masked, e->size);
  
  					kfree(masked);
  				}
  			}
  		}

  	} else {

  		/* Handle the 'E' (extension) format. */
  
  		/* Skip the 'offset' field. */

  		p = strchr(p, del);
  		if (!p)

  			goto einval;

  		*p++ = '\0';

  
  		/* Parse the 'magic' field. */

  		e->magic = p;
  		p = strchr(p, del);
  		if (!p)

  			goto einval;

  		*p++ = '\0';
  		if (!e->magic[0] || strchr(e->magic, '/'))

  			goto einval;

  		pr_debug("register: extension: {%s}
  ", e->magic);
  
  		/* Skip the 'mask' field. */

  		p = strchr(p, del);
  		if (!p)

  			goto einval;

  		*p++ = '\0';
  	}

  
  	/* Parse the 'interpreter' field. */

  	e->interpreter = p;
  	p = strchr(p, del);
  	if (!p)

  		goto einval;

  	*p++ = '\0';
  	if (!e->interpreter[0])

  		goto einval;

  	pr_debug("register: interpreter: {%s}
  ", e->interpreter);

  	/* Parse the 'flags' field. */

  	p = check_special_flags(p, e);

  	if (*p == '
  ')
  		p++;
  	if (p != buf + count)

  		goto einval;

  	return e;
  
  out:
  	return ERR_PTR(err);

  efault:

  	kfree(e);
  	return ERR_PTR(-EFAULT);

  einval:

  	kfree(e);
  	return ERR_PTR(-EINVAL);
  }
  
  /*
   * Set status of entry/binfmt_misc:
   * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
   */
  static int parse_command(const char __user *buffer, size_t count)
  {
  	char s[4];

  	if (count > 3)
  		return -EINVAL;
  	if (copy_from_user(s, buffer, count))
  		return -EFAULT;

  	if (!count)
  		return 0;

  	if (s[count - 1] == '
  ')

  		count--;
  	if (count == 1 && s[0] == '0')
  		return 1;
  	if (count == 1 && s[0] == '1')
  		return 2;
  	if (count == 2 && s[0] == '-' && s[1] == '1')
  		return 3;
  	return -EINVAL;
  }
  
  /* generic stuff */
  
  static void entry_status(Node *e, char *page)
  {

  	char *dp = page;
  	const char *status = "disabled";

  
  	if (test_bit(Enabled, &e->flags))
  		status = "enabled";
  
  	if (!VERBOSE_STATUS) {
  		sprintf(page, "%s
  ", status);
  		return;
  	}

  	dp += sprintf(dp, "%s
  interpreter %s
  ", status, e->interpreter);

  
  	/* print the special flags */

  	dp += sprintf(dp, "flags: ");

  	if (e->flags & MISC_FMT_PRESERVE_ARGV0)
  		*dp++ = 'P';
  	if (e->flags & MISC_FMT_OPEN_BINARY)
  		*dp++ = 'O';
  	if (e->flags & MISC_FMT_CREDENTIALS)
  		*dp++ = 'C';

  	if (e->flags & MISC_FMT_OPEN_FILE)
  		*dp++ = 'F';

  	*dp++ = '
  ';

  
  	if (!test_bit(Magic, &e->flags)) {
  		sprintf(dp, "extension .%s
  ", e->magic);
  	} else {

  		dp += sprintf(dp, "offset %i
  magic ", e->offset);
  		dp = bin2hex(dp, e->magic, e->size);

  		if (e->mask) {

  			dp += sprintf(dp, "
  mask ");
  			dp = bin2hex(dp, e->mask, e->size);

  		}
  		*dp++ = '
  ';
  		*dp = '\0';
  	}
  }
  
  static struct inode *bm_get_inode(struct super_block *sb, int mode)
  {

  	struct inode *inode = new_inode(sb);

  
  	if (inode) {

  		inode->i_ino = get_next_ino();

  		inode->i_mode = mode;

  		inode->i_atime = inode->i_mtime = inode->i_ctime =

  			current_time(inode);

  	}
  	return inode;
  }

  static void bm_evict_inode(struct inode *inode)

  {

  	Node *e = inode->i_private;

  	if (e && e->flags & MISC_FMT_OPEN_FILE)

  		filp_close(e->interp_file, NULL);

  	clear_inode(inode);

  	kfree(e);

  }
  
  static void kill_node(Node *e)
  {
  	struct dentry *dentry;
  
  	write_lock(&entries_lock);

  	list_del_init(&e->list);

  	write_unlock(&entries_lock);

  	dentry = e->dentry;
  	drop_nlink(d_inode(dentry));
  	d_drop(dentry);
  	dput(dentry);
  	simple_release_fs(&bm_mnt, &entry_count);

  }
  
  /* /<entry> */
  
  static ssize_t

  bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)

  {

  	Node *e = file_inode(file)->i_private;

  	ssize_t res;
  	char *page;

  	page = (char *) __get_free_page(GFP_KERNEL);
  	if (!page)

  		return -ENOMEM;
  
  	entry_status(e, page);

  	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));

  	free_page((unsigned long) page);
  	return res;
  }
  
  static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
  				size_t count, loff_t *ppos)
  {
  	struct dentry *root;

  	Node *e = file_inode(file)->i_private;

  	int res = parse_command(buffer, count);
  
  	switch (res) {

  	case 1:
  		/* Disable this handler. */
  		clear_bit(Enabled, &e->flags);
  		break;
  	case 2:
  		/* Enable this handler. */
  		set_bit(Enabled, &e->flags);
  		break;
  	case 3:
  		/* Delete this handler. */

  		root = file_inode(file)->i_sb->s_root;

  		inode_lock(d_inode(root));

  		if (!list_empty(&e->list))
  			kill_node(e);

  		inode_unlock(d_inode(root));

  		break;
  	default:
  		return res;

  	}

  	return count;
  }

  static const struct file_operations bm_entry_operations = {

  	.read		= bm_entry_read,
  	.write		= bm_entry_write,

  	.llseek		= default_llseek,

  };
  
  /* /register */
  
  static ssize_t bm_register_write(struct file *file, const char __user *buffer,
  			       size_t count, loff_t *ppos)
  {
  	Node *e;
  	struct inode *inode;

  	struct super_block *sb = file_inode(file)->i_sb;
  	struct dentry *root = sb->s_root, *dentry;

  	int err = 0;
  
  	e = create_entry(buffer, count);
  
  	if (IS_ERR(e))
  		return PTR_ERR(e);

  	inode_lock(d_inode(root));

  	dentry = lookup_one_len(e->name, root, strlen(e->name));
  	err = PTR_ERR(dentry);
  	if (IS_ERR(dentry))
  		goto out;
  
  	err = -EEXIST;

  	if (d_really_is_positive(dentry))

  		goto out2;
  
  	inode = bm_get_inode(sb, S_IFREG | 0644);
  
  	err = -ENOMEM;
  	if (!inode)
  		goto out2;

  	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);

  	if (err) {
  		iput(inode);
  		inode = NULL;
  		goto out2;
  	}

  	if (e->flags & MISC_FMT_OPEN_FILE) {
  		struct file *f;
  
  		f = open_exec(e->interpreter);
  		if (IS_ERR(f)) {
  			err = PTR_ERR(f);
  			pr_notice("register: failed to install interpreter file %s
  ", e->interpreter);
  			simple_release_fs(&bm_mnt, &entry_count);
  			iput(inode);
  			inode = NULL;
  			goto out2;
  		}
  		e->interp_file = f;
  	}

  	e->dentry = dget(dentry);

  	inode->i_private = e;

  	inode->i_fop = &bm_entry_operations;
  
  	d_instantiate(dentry, inode);
  	write_lock(&entries_lock);
  	list_add(&e->list, &entries);
  	write_unlock(&entries_lock);
  
  	err = 0;
  out2:
  	dput(dentry);
  out:

  	inode_unlock(d_inode(root));

  
  	if (err) {
  		kfree(e);

  		return err;

  	}
  	return count;
  }

  static const struct file_operations bm_register_operations = {

  	.write		= bm_register_write,

  	.llseek		= noop_llseek,

  };
  
  /* /status */
  
  static ssize_t
  bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
  {

  	char *s = enabled ? "enabled
  " : "disabled
  ";

  	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));

  }

  static ssize_t bm_status_write(struct file *file, const char __user *buffer,

  		size_t count, loff_t *ppos)
  {
  	int res = parse_command(buffer, count);
  	struct dentry *root;
  
  	switch (res) {

  	case 1:
  		/* Disable all handlers. */
  		enabled = 0;
  		break;
  	case 2:
  		/* Enable all handlers. */
  		enabled = 1;
  		break;
  	case 3:
  		/* Delete all handlers. */

  		root = file_inode(file)->i_sb->s_root;

  		inode_lock(d_inode(root));

  		while (!list_empty(&entries))

  			kill_node(list_first_entry(&entries, Node, list));

  		inode_unlock(d_inode(root));

  		break;
  	default:
  		return res;

  	}

  	return count;
  }

  static const struct file_operations bm_status_operations = {

  	.read		= bm_status_read,
  	.write		= bm_status_write,

  	.llseek		= default_llseek,

  };
  
  /* Superblock handling */

  static const struct super_operations s_ops = {

  	.statfs		= simple_statfs,

  	.evict_inode	= bm_evict_inode,

  };

  static int bm_fill_super(struct super_block *sb, struct fs_context *fc)

  {

  	int err;

  	static const struct tree_descr bm_files[] = {

  		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
  		[3] = {"register", &bm_register_operations, S_IWUSR},

  		/* last one */ {""}
  	};

  
  	err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);

  	if (!err)
  		sb->s_op = &s_ops;
  	return err;
  }

  static int bm_get_tree(struct fs_context *fc)

  {

  	return get_tree_single(fc, bm_fill_super);
  }
  
  static const struct fs_context_operations bm_context_ops = {
  	.get_tree	= bm_get_tree,
  };
  
  static int bm_init_fs_context(struct fs_context *fc)
  {
  	fc->ops = &bm_context_ops;
  	return 0;

  }
  
  static struct linux_binfmt misc_format = {
  	.module = THIS_MODULE,
  	.load_binary = load_misc_binary,
  };
  
  static struct file_system_type bm_fs_type = {
  	.owner		= THIS_MODULE,
  	.name		= "binfmt_misc",

  	.init_fs_context = bm_init_fs_context,

  	.kill_sb	= kill_litter_super,
  };

  MODULE_ALIAS_FS("binfmt_misc");

  
  static int __init init_misc_binfmt(void)
  {
  	int err = register_filesystem(&bm_fs_type);

  	if (!err)
  		insert_binfmt(&misc_format);

  	return err;
  }
  
  static void __exit exit_misc_binfmt(void)
  {
  	unregister_binfmt(&misc_format);
  	unregister_filesystem(&bm_fs_type);
  }
  
  core_initcall(init_misc_binfmt);
  module_exit(exit_misc_binfmt);
  MODULE_LICENSE("GPL");