/*
   *  binfmt_misc.c
   *

   *  Copyright (C) 1997 Richard Günther

   *
   *  binfmt_misc detects binaries via a magic or filename extension and invokes
   *  a specified wrapper. This should obsolete binfmt_java, binfmt_em86 and
   *  binfmt_mz.
   *
   *  1997-04-25 first version
   *  [...]
   *  1997-05-19 cleanup
   *  1997-06-26 hpa: pass the real filename rather than argv[0]
   *  1997-06-30 minor cleanup
   *  1997-08-09 removed extension stripping, locking cleanup
   *  2001-02-28 AV: rewritten into something that resembles C. Original didn't.
   */
  
  #include <linux/module.h>
  #include <linux/init.h>

  #include <linux/sched.h>

  #include <linux/binfmts.h>
  #include <linux/slab.h>
  #include <linux/ctype.h>
  #include <linux/file.h>
  #include <linux/pagemap.h>
  #include <linux/namei.h>
  #include <linux/mount.h>
  #include <linux/syscalls.h>

  #include <linux/fs.h>

  
  #include <asm/uaccess.h>
  
  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)
  
  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 */
  	char *interpreter;		/* filename of interpreter */
  	char *name;
  	struct dentry *dentry;
  } Node;
  
  static DEFINE_RWLOCK(entries_lock);

  static struct file_system_type bm_fs_type;

  static struct vfsmount *bm_mnt;
  static int entry_count;
  
  /* 
   * 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;
  
  	list_for_each(l, &entries) {
  		Node *e = list_entry(l, Node, list);
  		char *s;
  		int j;
  
  		if (!test_bit(Enabled, &e->flags))
  			continue;
  
  		if (!test_bit(Magic, &e->flags)) {
  			if (p && !strcmp(e->magic, p + 1))
  				return e;
  			continue;
  		}
  
  		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, struct pt_regs *regs)
  {
  	Node *fmt;
  	struct file * interp_file = NULL;
  	char iname[BINPRM_BUF_SIZE];

  	const char *iname_addr = iname;

  	int retval;
  	int fd_binary = -1;

  
  	retval = -ENOEXEC;
  	if (!enabled)
  		goto _ret;

  	retval = -ENOEXEC;

  	if (bprm->recursion_depth > BINPRM_MAX_RECURSION)

  		goto _ret;

  	/* to keep locking time low, we copy the interpreter string */
  	read_lock(&entries_lock);
  	fmt = check_file(bprm);
  	if (fmt)
  		strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
  	read_unlock(&entries_lock);
  	if (!fmt)
  		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) {

  		/* if the binary should be opened on behalf of the
  		 * interpreter than keep it open and assign descriptor
  		 * to it */
   		fd_binary = get_unused_fd();
   		if (fd_binary < 0) {
   			retval = fd_binary;

   			goto _ret;

   		}
   		fd_install(fd_binary, bprm->file);
  
  		/* if the binary is not readable than enforce mm->dumpable=0
  		   regardless of the interpreter's permissions */

  		would_dump(bprm, bprm->file);

  
  		allow_write_access(bprm->file);
  		bprm->file = NULL;
  
  		/* mark the bprm that fd should be passed to interp */
  		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
  		bprm->interp_data = fd_binary;
  
   	} else {
   		allow_write_access(bprm->file);
   		fput(bprm->file);
   		bprm->file = NULL;
   	}
  	/* make argv[1] be the path to the binary */
  	retval = copy_strings_kernel (1, &bprm->interp, bprm);
  	if (retval < 0)
  		goto _error;
  	bprm->argc++;
  
  	/* add the interp as argv[0] */
  	retval = copy_strings_kernel (1, &iname_addr, bprm);
  	if (retval < 0)
  		goto _error;
  	bprm->argc ++;
  
  	bprm->interp = iname;	/* for binfmt_script */
  
  	interp_file = open_exec (iname);
  	retval = PTR_ERR (interp_file);
  	if (IS_ERR (interp_file))
  		goto _error;
  
  	bprm->file = interp_file;
  	if (fmt->flags & MISC_FMT_CREDENTIALS) {
  		/*
  		 * No need to call prepare_binprm(), it's already been
  		 * done.  bprm->buf is stale, update from interp_file.
  		 */
  		memset(bprm->buf, 0, BINPRM_BUF_SIZE);
  		retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
  	} else
  		retval = prepare_binprm (bprm);
  
  	if (retval < 0)
  		goto _error;

  	bprm->recursion_depth++;

  	retval = search_binary_handler (bprm, regs);
  	if (retval < 0)
  		goto _error;

  _ret:
  	return retval;
  _error:
  	if (fd_binary > 0)
  		sys_close(fd_binary);
  	bprm->interp_flags = 0;
  	bprm->interp_data = 0;

  	goto _ret;
  }
  
  /* 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;
  		}
  	}
  	return s;
  }
  
  static int unquote(char *from)
  {
  	char c = 0, *s = from, *p = from;
  
  	while ((c = *s++) != '\0') {
  		if (c == '\\' && *s == 'x') {
  			s++;
  			c = toupper(*s++);
  			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
  			c = toupper(*s++);
  			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
  			continue;
  		}
  		*p++ = c;
  	}
  	return p - from;
  }

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

  {
  	char * p = sfs;
  	int cont = 1;
  
  	/* special flags */
  	while (cont) {
  		switch (*p) {
  			case 'P':
  				p++;
  				e->flags |= MISC_FMT_PRESERVE_ARGV0;
  				break;
  			case 'O':
  				p++;
  				e->flags |= MISC_FMT_OPEN_BINARY;
  				break;
  			case 'C':
  				p++;
  				/* this flags also implies the
  				   open-binary flag */
  				e->flags |= (MISC_FMT_CREDENTIALS |
  						MISC_FMT_OPEN_BINARY);
  				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;
  
  	/* some sanity checks */
  	err = -EINVAL;
  	if ((count < 11) || (count > 256))
  		goto out;
  
  	err = -ENOMEM;
  	memsize = sizeof(Node) + count + 8;

  	e = kmalloc(memsize, GFP_USER);

  	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 */
  
  	memset(buf+count, del, 8);
  
  	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;
  	switch (*p++) {
  		case 'E': e->flags = 1<<Enabled; break;
  		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
  		default: goto Einval;
  	}
  	if (*p++ != del)
  		goto Einval;
  	if (test_bit(Magic, &e->flags)) {
  		char *s = strchr(p, del);
  		if (!s)
  			goto Einval;
  		*s++ = '\0';
  		e->offset = simple_strtoul(p, &p, 10);
  		if (*p++)
  			goto Einval;
  		e->magic = p;
  		p = scanarg(p, del);
  		if (!p)
  			goto Einval;
  		p[-1] = '\0';
  		if (!e->magic[0])
  			goto Einval;
  		e->mask = p;
  		p = scanarg(p, del);
  		if (!p)
  			goto Einval;
  		p[-1] = '\0';
  		if (!e->mask[0])
  			e->mask = NULL;
  		e->size = unquote(e->magic);
  		if (e->mask && unquote(e->mask) != e->size)
  			goto Einval;
  		if (e->size + e->offset > BINPRM_BUF_SIZE)
  			goto Einval;
  	} else {
  		p = strchr(p, del);
  		if (!p)
  			goto Einval;
  		*p++ = '\0';
  		e->magic = p;
  		p = strchr(p, del);
  		if (!p)
  			goto Einval;
  		*p++ = '\0';
  		if (!e->magic[0] || strchr(e->magic, '/'))
  			goto Einval;
  		p = strchr(p, del);
  		if (!p)
  			goto Einval;
  		*p++ = '\0';
  	}
  	e->interpreter = p;
  	p = strchr(p, del);
  	if (!p)
  		goto Einval;
  	*p++ = '\0';
  	if (!e->interpreter[0])
  		goto Einval;
  
  
  	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)
  		return 0;
  	if (count > 3)
  		return -EINVAL;
  	if (copy_from_user(s, buffer, count))
  		return -EFAULT;
  	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;
  	char *status = "disabled";
  	const char * flags = "flags: ";
  
  	if (test_bit(Enabled, &e->flags))
  		status = "enabled";
  
  	if (!VERBOSE_STATUS) {
  		sprintf(page, "%s
  ", status);
  		return;
  	}
  
  	sprintf(page, "%s
  interpreter %s
  ", status, e->interpreter);
  	dp = page + strlen(page);
  
  	/* print the special flags */
  	sprintf (dp, "%s", flags);
  	dp += strlen (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';
  	}
  	*dp ++ = '
  ';
  
  
  	if (!test_bit(Magic, &e->flags)) {
  		sprintf(dp, "extension .%s
  ", e->magic);
  	} else {
  		int i;
  
  		sprintf(dp, "offset %i
  magic ", e->offset);
  		dp = page + strlen(page);
  		for (i = 0; i < e->size; i++) {
  			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
  			dp += 2;
  		}
  		if (e->mask) {
  			sprintf(dp, "
  mask ");
  			dp += 6;
  			for (i = 0; i < e->size; i++) {
  				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
  				dp += 2;
  			}
  		}
  		*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_fs_time(inode->i_sb);
  	}
  	return inode;
  }

  static void bm_evict_inode(struct inode *inode)

  {

  	end_writeback(inode);

  	kfree(inode->i_private);

  }
  
  static void kill_node(Node *e)
  {
  	struct dentry *dentry;
  
  	write_lock(&entries_lock);
  	dentry = e->dentry;
  	if (dentry) {
  		list_del_init(&e->list);
  		e->dentry = NULL;
  	}
  	write_unlock(&entries_lock);
  
  	if (dentry) {
  		dentry->d_inode->i_nlink--;
  		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->f_path.dentry->d_inode->i_private;

  	ssize_t res;
  	char *page;

  
  	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
  		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->f_path.dentry->d_inode->i_private;

  	int res = parse_command(buffer, count);
  
  	switch (res) {
  		case 1: clear_bit(Enabled, &e->flags);
  			break;
  		case 2: set_bit(Enabled, &e->flags);
  			break;

  		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);

  			mutex_lock(&root->d_inode->i_mutex);

  
  			kill_node(e);

  			mutex_unlock(&root->d_inode->i_mutex);

  			dput(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 dentry *root, *dentry;

  	struct super_block *sb = file->f_path.mnt->mnt_sb;

  	int err = 0;
  
  	e = create_entry(buffer, count);
  
  	if (IS_ERR(e))
  		return PTR_ERR(e);
  
  	root = dget(sb->s_root);

  	mutex_lock(&root->d_inode->i_mutex);

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

  	mutex_unlock(&root->d_inode->i_mutex);

  	dput(root);
  
  	if (err) {
  		kfree(e);
  		return -EINVAL;
  	}
  	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: enabled = 0; break;
  		case 2: enabled = 1; break;

  		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);

  			mutex_lock(&root->d_inode->i_mutex);

  
  			while (!list_empty(&entries))
  				kill_node(list_entry(entries.next, Node, list));

  			mutex_unlock(&root->d_inode->i_mutex);

  			dput(root);
  		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, void * data, int silent)
  {
  	static struct tree_descr bm_files[] = {

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

  		/* last one */ {""}
  	};
  	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
  	if (!err)
  		sb->s_op = &s_ops;
  	return err;
  }

  static struct dentry *bm_mount(struct file_system_type *fs_type,
  	int flags, const char *dev_name, void *data)

  {

  	return mount_single(fs_type, flags, data, bm_fill_super);

  }
  
  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",

  	.mount		= bm_mount,

  	.kill_sb	= kill_litter_super,
  };
  
  static int __init init_misc_binfmt(void)
  {
  	int err = register_filesystem(&bm_fs_type);
  	if (!err) {

  		err = insert_binfmt(&misc_format);

  		if (err)
  			unregister_filesystem(&bm_fs_type);
  	}
  	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");