[Xen-devel] qemu/fdc: Sector size overflow

[Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>]

Hi:

[QEMU] fdc: Limit sector size to 16K

In fdctrl_start_transfer the sector size field (fifo[5]) is not checked
for overflows.  This allows an arbitrarily large sector size to be used,
which can in turn result in a negative data_len field that is then used
for DMA transfers.

This can lead to the corrpuption of qemu state because some subsequent
checks on the transfer length is conducted using signed integers.

This patch limits the value fifo[5] to 7 which is the standard limit
on floppy sector size.

Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx>
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--
diff -r 91951de7592c tools/ioemu/hw/fdc.c
--- a/tools/ioemu/hw/fdc.c      Sun Nov 26 17:35:00 2006 +0000
+++ b/tools/ioemu/hw/fdc.c      Mon Nov 27 14:47:31 2006 +1100
@@ -898,7 +898,7 @@ static void fdctrl_start_transfer (fdctr
         fdctrl->data_len = fdctrl->fifo[8];
     } else {
        int tmp;
-        fdctrl->data_len = 128 << fdctrl->fifo[5];
+        fdctrl->data_len = 128 << (fdctrl->fifo[5] > 7 ? 7 : fdctrl->fifo[5]);
         tmp = (cur_drv->last_sect - ks + 1);
         if (fdctrl->fifo[0] & 0x80)
             tmp += cur_drv->last_sect;

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