path: root/hivex/hivex.pod

=encoding utf8

=head1 NAME

hivex - Windows Registry "hive" extraction library

=head1 SYNOPSIS

 hive_h *hivex_open (const char *filename, int flags);
 int hivex_close (hive_h *h);

=head1 DESCRIPTION

libhivex is a library for extracting the contents of Windows Registry
"hive" files.  It is designed to be secure against buggy or malicious
registry files, and to have limited functionality (writing or
modifying these files is not in the scope of this library).

Unlike many other tools in this area, it doesn't use the textual .REG
format for output, because parsing that is as much trouble as parsing
the original binary format.  Instead it makes the file available
through a C API, or there is a separate program to export the hive as
XML (see L<hivexml(1)>), or to get individual keys (see
L<hivexget(1)>).

=head2 OPENING AND CLOSING A HIVE

=over 4

=item hive_h *hivex_open (const char *filename, int flags);

Opens the hive named C<filename> for reading.

Flags is an ORed list of the open flags (or C<0> if you don't
want to pass any flags).  Currently the only
flags defined are:

=over 4

=item HIVEX_OPEN_VERBOSE

Verbose messages.

=item HIVEX_OPEN_DEBUG

Very verbose messages, suitable for debugging problems in the library
itself.

This is also selected if the C<HIVEX_DEBUG> environment variable
is set to 1.

=back

C<hivex_open> returns a hive handle.  On error this returns NULL and
sets C<errno> to indicate the error.

=item int hivex_close (hive_h *h);

Close a hive handle and free all associated resources.

Returns 0 on success.  On error this returns -1 and sets errno.

=back

=head2 NAVIGATING THE TREE OF HIVE SUBKEYS

=over 4

=item hive_node_h hivex_root (hive_h *h);

Return root node of the hive.  All valid registries must contain
a root node.

On error this returns 0 and sets errno.

=item char *hivex_node_name (hive_h *h, hive_node_h node);

Return the name of the node.  The name is reencoded as UTF-8
and returned as a C string.

The string should be freed by the caller when it is no longer needed.

Note that the name of the root node is a dummy, such as
C<$$$PROTO.HIV> (other names are possible: it seems to depend on the
tool or program that created the hive in the first place).  You can
only know the "real" name of the root node by knowing which registry
file this hive originally comes from, which is knowledge that is
outside the scope of this library.

On error this returns NULL and sets errno.

=item hive_node_h *hivex_node_children (hive_h *h, hive_node_h node);

Return a 0-terminated array of nodes which are the subkeys
(children) of C<node>.

The array should be freed by the caller when it is no longer needed.

On error this returns NULL and sets errno.

=item hive_node_h hivex_node_get_child (hive_h *h, hive_node_h node, const char *name);

Return the child of node with the name C<name>, if it exists.

The name is matched case insensitively.

If the child node does not exist, this returns 0 without
setting errno.

On error this returns 0 and sets errno.

=item hive_node_h hivex_node_parent (hive_h *h, hive_node_h node);

Return the parent of C<node>.

On error this returns 0 and sets errno.

The parent pointer of the root node in registry files that we
have examined seems to be invalid, and so this function will
return an error if called on the root node.

=back

=head2 GETTING VALUES AT A NODE

The enum below describes the possible types for the value(s)
stored at each node.

 enum hive_type {
   hive_t_none = 0,
   hive_t_string = 1,
   hive_t_expand_string = 2,
   hive_t_binary = 3,
   hive_t_dword = 4,
   hive_t_dword_be = 5,
   hive_t_link = 6,
   hive_t_multiple_strings = 7,
   hive_t_resource_list = 8,
   hive_t_full_resource_description = 9,
   hive_t_resource_requirements_list = 10,
   hive_t_qword = 11
 };

=over 4

=item hive_value_h *hivex_node_values (hive_h *h, hive_node_h node);

Return the 0-terminated array of (key, value) pairs attached to
this node.

The array should be freed by the caller when it is no longer needed.

On error this returns NULL and sets errno.

=item hive_value_h hivex_node_get_value (hive_h *h, hive_node_h node, const char *key);

Return the value attached to this node which has the name C<key>,
if it exists.

The key name is matched case insensitively.

Note that to get the default key, you should pass the empty
string C<""> here.  The default key is often written C<"@">, but
inside hives that has no meaning and won't give you the
default key.

If no such key exists, this returns 0 and does not set errno.

On error this returns 0 and sets errno.

=item char *hivex_value_key (hive_h *h, hive_value_h value);

Return the key (name) of a (key, value) pair.  The name
is reencoded as UTF-8 and returned as a C string.

The string should be freed by the caller when it is no longer needed.

Note that this function can return a zero-length string.  In the
context of Windows Registries, this means that this value is the
default key for this node in the tree.  This is usually written
as C<"@">.

On error this returns NULL and sets errno.

=item int hivex_value_type (hive_h *h, hive_value_h value, hive_type *t, size_t *len);

Return the data type and length of the value in this (key, value)
pair.  See also C<hivex_value_value> which returns all this
information, and the value itself.  Also, C<hivex_value_*> functions
below which can be used to return the value in a more useful form when
you know the type in advance.

Returns 0 on success.  On error this returns -1 and sets errno.

=item char *hivex_value_value (hive_h *h, hive_value_h value, hive_type *t, size_t *len);

Return the value of this (key, value) pair.  The value should
be interpreted according to its type (see C<hive_type>).

The value is returned in an array of bytes of length C<len>.

The value should be freed by the caller when it is no longer needed.

On error this returns NULL and sets errno.

=item char *hivex_value_string (hive_h *h, hive_value_h value);

If this value is a string, return the string reencoded as UTF-8
(as a C string).  This only works for values which have type
C<hive_t_string>, C<hive_t_expand_string> or C<hive_t_link>.

The string should be freed by the caller when it is no longer needed.

On error this returns NULL and sets errno.

=item char **hivex_value_multiple_strings (hive_h *h, hive_value_h value);

If this value is a multiple-string, return the strings reencoded
as UTF-8 (as a NULL-terminated array of C strings).  This only
works for values which have type C<hive_t_multiple_strings>.

The string array and each string in it should be freed by the
caller when they are no longer needed.

On error this returns NULL and sets errno.

=item int32_t hivex_value_dword (hive_h *h, hive_value_h value);

If this value is a DWORD (Windows int32), return it.  This only works
for values which have type C<hive_t_dword> or C<hive_t_dword_be>.

=item int64_t hivex_value_qword (hive_h *h, hive_value_h value);

If this value is a QWORD (Windows int64), return it.  This only
works for values which have type C<hive_t_qword>.

=back

=head2 VISITING ALL NODES

The visitor pattern is useful if you want to visit all nodes
in the tree or all nodes below a certain point in the tree.

First you set up your own C<struct hivex_visitor> with your
callback functions.

Each of these callback functions should return 0 on success or -1
on error.  If any callback returns -1, then the entire visit
terminates immediately.  If you don't need a callback function at
all, set the function pointer to NULL.

 struct hivex_visitor {
   int (*node_start) (hive_h *, void *opaque, hive_node_h, const char *name);
   int (*node_end) (hive_h *, void *opaque, hive_node_h, const char *name);
   int (*value_string) (hive_h *, void *opaque, hive_node_h, hive_value_h,
         hive_type t, size_t len, const char *key, const char *str);
   int (*value_multiple_strings) (hive_h *, void *opaque, hive_node_h,
         hive_value_h, hive_type t, size_t len, const char *key, char **argv);
   int (*value_string_invalid_utf16) (hive_h *, void *opaque, hive_node_h,
         hive_value_h, hive_type t, size_t len, const char *key,
         const char *str);
   int (*value_dword) (hive_h *, void *opaque, hive_node_h, hive_value_h,
         hive_type t, size_t len, const char *key, int32_t);
   int (*value_qword) (hive_h *, void *opaque, hive_node_h, hive_value_h,
         hive_type t, size_t len, const char *key, int64_t);
   int (*value_binary) (hive_h *, void *opaque, hive_node_h, hive_value_h,
         hive_type t, size_t len, const char *key, const char *value);
   int (*value_none) (hive_h *, void *opaque, hive_node_h, hive_value_h,
         hive_type t, size_t len, const char *key, const char *value);
   int (*value_other) (hive_h *, void *opaque, hive_node_h, hive_value_h,
         hive_type t, size_t len, const char *key, const char *value);
 };

=over 4

=item int hivex_visit (hive_h *h, const struct hivex_visitor *visitor, size_t len, void *opaque, int flags);

Visit all the nodes recursively in the hive C<h>.

C<visitor> should be a C<hivex_visitor> structure with callback
fields filled in as required (unwanted callbacks can be set to
NULL).  C<len> must be the length of the 'visitor' struct (you
should pass C<sizeof (struct hivex_visitor)> for this).

This returns 0 if the whole recursive visit was completed
successfully.  On error this returns -1.  If one of the callback
functions returned an error than we don't touch errno.  If the
error was generated internally then we set errno.

You can skip bad registry entries by setting C<flag> to
C<HIVEX_VISIT_SKIP_BAD>.  If this flag is not set, then a bad registry
causes the function to return an error immediately.

This function is robust if the registry contains cycles or
pointers which are invalid or outside the registry.  It detects
these cases and returns an error.

=item int hivex_visit_node (hive_h *h, hive_node_h node, const struct hivex_visitor *visitor, size_t len, void *opaque);

Same as C<hivex_visit> but instead of starting out at the root, this
starts at C<node>.

=back

=head1 THE STRUCTURE OF THE WINDOWS REGISTRY

Note: To understand the relationship between hives and the common
Windows Registry keys (like C<HKEY_LOCAL_MACHINE>) please see the
Wikipedia page on the Windows Registry.

The Windows Registry is split across various binary files, each
file being known as a "hive".  This library only handles a single
hive file at a time.

Hives are n-ary trees with a single root.  Each node in the tree
has a name.

Each node in the tree (including non-leaf nodes) may have an
arbitrary list of (key, value) pairs attached to it.  It may
be the case that one of these pairs has an empty key.  This
is referred to as the default key for the node.

The (key, value) pairs are the place where the useful data is
stored in the registry.  The key is always a string (possibly the
empty string for the default key).  The value is a typed object
(eg. string, int32, binary, etc.).

=head1 NOTE ON THE USE OF ERRNO

Many functions in this library set errno to indicate errors.
These are the values of errno you may encounter:

=over 4

=item ENOTSUP

Corrupt or unsupported Registry file format.

=item ENOKEY

Missing root key.

=item EINVAL

Passed an invalid argument to the function.

=item EFAULT

Followed a Registry pointer which goes outside
the registry or outside a registry block.

=item ELOOP

Registry contains cycles.

=item ERANGE

Field in the registry out of range.

=back

=head1 SEE ALSO

L<hivexml(1)>,
L<hivexget(1)>,
L<virt-win-reg(1)>,
L<guestfs(3)>,
L<http://libguestfs.org/>,
L<virt-cat(1)>,
L<virt-edit(1)>.

=head1 AUTHORS

Richard W.M. Jones (C<rjones at redhat dot com>)

=head1 COPYRIGHT

Copyright (C) 2009 Red Hat Inc.

Derived from code by Petter Nordahl-Hagen under a compatible license:
Copyright (c) 1997-2007 Petter Nordahl-Hagen.

Derived from code by Markus Stephany under a compatible license:
Copyright (c)2000-2004, Markus Stephany.

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation;
version 2.1 of the License.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.

See file LICENSE for the full license.