sd: sdhci: check data length during dma_memory_read

While doing multi block SDMA transfer in routine
'sdhci_sdma_transfer_multi_blocks', the 's->fifo_buffer' starting
index 'begin' and data length 's->data_count' could end up to be same.
This could lead to an OOB access issue. Correct transfer data length
to avoid it.

Cc: qemu-stable@nongnu.org
Reported-by: NJiang Xin <jiangxin1@huawei.com>
Signed-off-by: NPrasad J Pandit <pjp@fedoraproject.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 20170130064736.9236-1-ppandit@redhat.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
(cherry picked from commit 42922105)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

hw/sd/sdhci.c

@@ -536,7 +536,7 @@ static void sdhci_sdma_transfer_multi_blocks(SDHCIState *s)
                 boundary_count -= block_size - begin;
             }
             dma_memory_read(&address_space_memory, s->sdmasysad,
-                            &s->fifo_buffer[begin], s->data_count);
+                            &s->fifo_buffer[begin], s->data_count - begin);
             s->sdmasysad += s->data_count - begin;
             if (s->data_count == block_size) {
                 for (n = 0; n < block_size; n++) {