ALSA: emu10k1: Avoid access to invalid pages when period=1

When period=1, the driver tries to allocate a bit bigger buffer than
requested by the user due to the irq latency tolerance.  This may lead
to accesses over the actually allocated pages.

This patch adds a check of the page index and assigns the silent page
when it's over the given buffer size.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/emu10k1/memory.c

@@ -326,7 +326,10 @@ snd_emu10k1_alloc_pages(struct snd_emu10k1 *emu, struct snd_pcm_substream *subst
 	for (page = blk->first_page; page <= blk->last_page; page++, idx++) {
 		unsigned long ofs = idx << PAGE_SHIFT;
 		dma_addr_t addr;
-		addr = snd_pcm_sgbuf_get_addr(substream, ofs);
+		if (ofs >= runtime->dma_bytes)
+			addr = emu->silent_page.addr;
+		else
+			addr = snd_pcm_sgbuf_get_addr(substream, ofs);
 		if (! is_valid_page(emu, addr)) {
 			printk(KERN_ERR "emu: failure page = %d\n", idx);
 			mutex_unlock(&hdr->block_mutex);