Subject: Re: [PATCH net-next 13/15] netfilter: nfdbus: Add D-bus message parsing

From: Pablo Neira Ayuso <[email-masked]>
Date: Fri, 29 Jun 2012 19:11:08 +0200

On Fri, Jun 29, 2012 at 05:45:52PM +0100, Vincent Sanders wrote:
> From: Javier Martinez Canillas <[email-masked]>
> 
> The netfilter D-Bus module needs to parse D-bus messages sent by
> applications to decide whether a peer can receive or not a D-Bus
> message. Add D-bus message parsing logic to be able to analyze.

Not talking about the entire patchset, only about the part I'm
responsible for.

I don't see why you think this belong to netfilter at all.

This doesn't integrate into the existing filtering infrastructure,
neither it extends it in any way.

> Signed-off-by: Javier Martinez Canillas <[email-masked]>
> Signed-off-by: Alban Crequy <[email-masked]>
> ---
>  net/netfilter/nfdbus/message.c |  194 ++++++++++++++++++++++++++++++++++++++++
>  net/netfilter/nfdbus/message.h |   71 +++++++++++++++
>  2 files changed, 265 insertions(+)
>  create mode 100644 net/netfilter/nfdbus/message.c
>  create mode 100644 net/netfilter/nfdbus/message.h
> 
> diff --git a/net/netfilter/nfdbus/message.c b/net/netfilter/nfdbus/message.c
> new file mode 100644
> index 0000000..93c409c
> --- /dev/null
> +++ b/net/netfilter/nfdbus/message.c
> @@ -0,0 +1,194 @@
> +/*
> + * message.c  Basic D-Bus message parsing
> + *
> + * Copyright (C) 2010-2012  Collabora Ltd
> + * Authors:	Alban Crequy <[email-masked]>
> + * Copyright (C) 2002, 2003, 2004, 2005  Red Hat Inc.
> + * Copyright (C) 2002, 2003  CodeFactory AB
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program 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 General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + *
> + */
> +
> +#include <linux/slab.h>
> +
> +#include "message.h"
> +
> +int dbus_message_type_from_string(const char *type_str)
> +{
> +	if (strcmp(type_str, "method_call") == 0)
> +		return DBUS_MESSAGE_TYPE_METHOD_CALL;
> +	if (strcmp(type_str, "method_return") == 0)
> +		return DBUS_MESSAGE_TYPE_METHOD_RETURN;
> +	else if (strcmp(type_str, "signal") == 0)
> +		return DBUS_MESSAGE_TYPE_SIGNAL;
> +	else if (strcmp(type_str, "error") == 0)
> +		return DBUS_MESSAGE_TYPE_ERROR;
> +	else
> +		return DBUS_MESSAGE_TYPE_INVALID;
> +}
> +
> +int dbus_message_parse(unsigned char *message, size_t len,
> +		       struct dbus_message *dbus_message)
> +{
> +	unsigned char *cur;
> +	int array_header_len;
> +
> +	dbus_message->message = message;
> +
> +	if (len < 4 + 4 + 4 + 4 || message[1] == 0 || message[1] > 4)
> +		return -EINVAL;
> +
> +	dbus_message->type = message[1];
> +	dbus_message->body_length = *((u32 *)(message + 4));
> +	cur = message + 12;
> +	array_header_len = *(u32 *)cur;
> +	dbus_message->len_offset = 12;
> +	cur += 4;
> +	while (cur < message + len
> +	       && cur < message + 12 + 4 + array_header_len) {
> +		int header_code;
> +		int signature_len;
> +		unsigned char *signature;
> +		int str_len;
> +		unsigned char *str;
> +
> +		/* D-Bus alignment craziness */
> +		if ((cur - message) % 8 != 0)
> +			cur += 8 - (cur - message) % 8;
> +
> +		header_code = *(char *)cur;
> +		cur++;
> +		signature_len = *(char *)cur;
> +		/* All header fields of the current D-Bus spec have a simple
> +		 * type, either o, s, g, or u */
> +		if (signature_len != 1)
> +			return -EINVAL;
> +		cur++;
> +		signature = cur;
> +		cur += signature_len + 1;
> +		if (signature[0] != 'o' &&
> +		    signature[0] != 's' &&
> +		    signature[0] != 'g' &&
> +		    signature[0] != 'u')
> +			return -EINVAL;
> +
> +		if (signature[0] == 'u') {
> +			cur += 4;
> +			continue;
> +		}
> +
> +		if (signature[0] != 'g') {
> +			str_len = *(u32 *)cur;
> +			cur += 4;
> +		} else {
> +			str_len = *(char *)cur;
> +			cur += 1;
> +		}
> +
> +		str = cur;
> +		switch (header_code) {
> +		case 1:
> +			dbus_message->path = str;
> +			break;
> +		case 2:
> +			dbus_message->interface = str;
> +			break;
> +		case 3:
> +			dbus_message->member = str;
> +			break;
> +		case 6:
> +			dbus_message->destination = str;
> +			break;
> +		case 7:
> +			dbus_message->sender = str;
> +			break;
> +		case 8:
> +			dbus_message->body_signature = str;
> +			break;
> +		}
> +		cur += str_len + 1;
> +	}
> +
> +	dbus_message->padding_end = (8 - (cur - message) % 8) % 8;
> +
> +	/* Jump to body D-Bus alignment craziness */
> +	if ((cur - message) % 8 != 0)
> +		cur += 8 - (cur - message) % 8;
> +	dbus_message->new_header_offset = cur - message;
> +
> +	if (dbus_message->new_header_offset
> +	    + dbus_message->body_length != len) {
> +		pr_warn("Message truncated? " \
> +			"Header %d + Body %d != Length %zd\n",
> +			dbus_message->new_header_offset,
> +			dbus_message->body_length, len);
> +		return -EINVAL;
> +	}
> +
> +	if (dbus_message->body_signature &&
> +	    dbus_message->body_signature[0] == 's') {
> +		int str_len;
> +		str_len = *(u32 *)cur;
> +		cur += 4;
> +		dbus_message->arg0 = cur;
> +		cur += str_len + 1;
> +	}
> +
> +	if ((cur - message) % 4 != 0)
> +		cur += 4 - (cur - message) % 4;
> +
> +	if (dbus_message->body_signature &&
> +	    dbus_message->body_signature[0] == 's' &&
> +	    dbus_message->body_signature[1] == 's') {
> +		int str_len;
> +		str_len = *(u32 *)cur;
> +		cur += 4;
> +		dbus_message->arg1 = cur;
> +		cur += str_len + 1;
> +	}
> +
> +	if ((cur - message) % 4 != 0)
> +		cur += 4 - (cur - message) % 4;
> +
> +	if (dbus_message->body_signature &&
> +	    dbus_message->body_signature[0] == 's' &&
> +	    dbus_message->body_signature[1] == 's' &&
> +	    dbus_message->body_signature[2] == 's') {
> +		int str_len;
> +		str_len = *(u32 *)cur;
> +		cur += 4;
> +		dbus_message->arg2 = cur;
> +		cur += str_len + 1;
> +	}
> +
> +	if ((cur - message) % 4 != 0)
> +		cur += 4 - (cur - message) % 4;
> +
> +	if (dbus_message->type == DBUS_MESSAGE_TYPE_SIGNAL &&
> +	    dbus_message->sender && dbus_message->path &&
> +	    dbus_message->interface && dbus_message->member &&
> +	    dbus_message->arg0 &&
> +	    strcmp(dbus_message->sender, "org.freedesktop.DBus") == 0 &&
> +	    strcmp(dbus_message->interface, "org.freedesktop.DBus") == 0 &&
> +	    strcmp(dbus_message->path, "/org/freedesktop/DBus") == 0) {
> +		if (strcmp(dbus_message->member, "NameAcquired") == 0)
> +			dbus_message->name_acquired = dbus_message->arg0;
> +		else if (strcmp(dbus_message->member, "NameLost") == 0)
> +			dbus_message->name_lost = dbus_message->arg0;
> +	}
> +
> +	return 0;
> +}
> diff --git a/net/netfilter/nfdbus/message.h b/net/netfilter/nfdbus/message.h
> new file mode 100644
> index 0000000..e3ea4d3
> --- /dev/null
> +++ b/net/netfilter/nfdbus/message.h
> @@ -0,0 +1,71 @@
> +/*
> + * message.h  Basic D-Bus message parsing
> + *
> + * Copyright (C) 2010  Collabora Ltd
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program 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 General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + *
> + */
> +
> +#ifndef DBUS_MESSAGE_H
> +#define DBUS_MESSAGE_H
> +
> +#include <linux/list.h>
> +
> +#define DBUS_MAXIMUM_MATCH_RULE_LENGTH 1024
> +
> +/* Types of message */
> +
> +#define DBUS_MESSAGE_TYPE_INVALID       0
> +#define DBUS_MESSAGE_TYPE_METHOD_CALL   1
> +#define DBUS_MESSAGE_TYPE_METHOD_RETURN 2
> +#define DBUS_MESSAGE_TYPE_ERROR         3
> +#define DBUS_MESSAGE_TYPE_SIGNAL        4
> +#define DBUS_NUM_MESSAGE_TYPES          5
> +
> +/* No need to implement a feature-complete parser. It only implement what is
> + * needed by the bus. */
> +struct dbus_message {
> +	char *message;
> +	size_t len;
> +	size_t new_len;
> +
> +	/* direct pointers to the fields */
> +	int type;
> +	char *path;
> +	char *interface;
> +	char *member;
> +	char *destination;
> +	char *sender;
> +	char *body_signature;
> +	int body_length;
> +	char *arg0;
> +	char *arg1;
> +	char *arg2;
> +	char *name_acquired;
> +	char *name_lost;
> +
> +	/* How to add the 'sender' field in the headers */
> +	int new_header_offset;
> +	int len_offset;
> +	int padding_end;
> +};
> +
> +int dbus_message_type_from_string(const char *type_str);
> +
> +int dbus_message_parse(unsigned char *message, size_t len,
> +		       struct dbus_message *dbus_message);
> +
> +#endif /* DBUS_MESSAGE_H */
> -- 
> 1.7.10
> 
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