From e907746266721f305d67bc0718795fedee2e824c Mon Sep 17 00:00:00 2001 From: Petr Matousek Date: Wed, 6 May 2015 09:48:59 +0200 Subject: [PATCH] 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: Petr Matousek Reviewed-by: John Snow Signed-off-by: John Snow --- hw/block/fdc.c | 17 +++++++++++------ 1 files changed, 11 insertions(+), 6 deletions(-) diff --git a/hw/block/fdc.c b/hw/block/fdc.c index f72a392..d8a8edd 100644 --- a/hw/block/fdc.c +++ b/hw/block/fdc.c @@ -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; + pos %= FD_SECTOR_LEN; if (fdctrl->msr & FD_MSR_NONDMA) { - pos %= FD_SECTOR_LEN; 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 -- 1.7.0.4