Commit e9077462 authored by Petr Matousek's avatar Petr Matousek Committed by John Snow
Browse files

fdc: force the fifo access to be in bounds of the allocated buffer 



During processing of certain commands such as FD_CMD_READ_ID and
FD_CMD_DRIVE_SPECIFICATION_COMMAND the fifo memory access could
get out of bounds leading to memory corruption with values coming
from the guest.

Fix this by making sure that the index is always bounded by the
allocated memory.

This is CVE-2015-3456.

Signed-off-by: default avatarPetr Matousek <pmatouse@redhat.com>
Reviewed-by: default avatarJohn Snow <jsnow@redhat.com>
Signed-off-by: default avatarJohn Snow <jsnow@redhat.com>
parent 968bb75c

hw/block/fdc.c

+11 −6
Original line number Diff line number Diff line
@@ -1497,7 +1497,7 @@ static uint32_t fdctrl_read_data(FDCtrl *fdctrl) 
{

    FDrive *cur_drv;

    uint32_t retval = 0;

    int pos;

    uint32_t pos;



    cur_drv = get_cur_drv(fdctrl);

    fdctrl->dsr &= ~FD_DSR_PWRDOWN;
@@ -1506,8 +1506,8 @@ static uint32_t fdctrl_read_data(FDCtrl *fdctrl) 
        return 0;

    }

    pos = fdctrl->data_pos;

    if (fdctrl->msr & FD_MSR_NONDMA) {

    pos %= FD_SECTOR_LEN;

    if (fdctrl->msr & FD_MSR_NONDMA) {

        if (pos == 0) {

            if (fdctrl->data_pos != 0)

                if (!fdctrl_seek_to_next_sect(fdctrl, cur_drv)) {
@@ -1852,10 +1852,13 @@ static void fdctrl_handle_option(FDCtrl *fdctrl, int direction) 
static void fdctrl_handle_drive_specification_command(FDCtrl *fdctrl, int direction)

{

    FDrive *cur_drv = get_cur_drv(fdctrl);

    uint32_t pos;



    if (fdctrl->fifo[fdctrl->data_pos - 1] & 0x80) {

    pos = fdctrl->data_pos - 1;

    pos %= FD_SECTOR_LEN;

    if (fdctrl->fifo[pos] & 0x80) {

        /* Command parameters done */

        if (fdctrl->fifo[fdctrl->data_pos - 1] & 0x40) {

        if (fdctrl->fifo[pos] & 0x40) {

            fdctrl->fifo[0] = fdctrl->fifo[1];

            fdctrl->fifo[2] = 0;

            fdctrl->fifo[3] = 0;
@@ -1955,7 +1958,7 @@ static uint8_t command_to_handler[256]; 
static void fdctrl_write_data(FDCtrl *fdctrl, uint32_t value)

{

    FDrive *cur_drv;

    int pos;

    uint32_t pos;



    /* Reset mode */

    if (!(fdctrl->dor & FD_DOR_nRESET)) {
@@ -2004,7 +2007,9 @@ static void fdctrl_write_data(FDCtrl *fdctrl, uint32_t value) 
    }



    FLOPPY_DPRINTF("%s: %02x\n", __func__, value);

    fdctrl->fifo[fdctrl->data_pos++] = value;

    pos = fdctrl->data_pos++;

    pos %= FD_SECTOR_LEN;

    fdctrl->fifo[pos] = value;

    if (fdctrl->data_pos == fdctrl->data_len) {

        /* We now have all parameters

         * and will be able to treat the command