linux-kernel - Re: [PATCH] ALSA: core: fix unsigned int pages overflow when comapred

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Date:   Wed, 18 Jul 2018 14:34:28 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     " He, Bo " <bo.he@...el.com>
Cc:     "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "perex@...ex.cz" <perex@...ex.cz>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jun Zhang" <jun.zhang@...el.com>,
        "Yanmin Zhang" <yanmin.zhang@...el.com>
Subject: Re: [PATCH] ALSA: core: fix unsigned int pages overflow when comapred

On Wed, 18 Jul 2018 13:52:45 +0200,
 He, Bo  wrote:
> 
> we see the below kernel panic on stress suspend resume test in
> snd_malloc_sgbuf_pages(), snd_dma_alloc_pages_fallback() alloc
> chunk maybe larger than the left pages due to the pages alignment,
> which will cause the pages overflow.
> 
> while (pages > 0) {
> 	...
> 	pages -= chunk;
> }
> 
> the patch is change the pages from unsigned int to int to fix the issue.

Thanks for the patch.

Although the analysis is correct, the fix doesn't look ideal.  It's
also possible that the returned size may over sgbuf->tblsize if we are
more unlucky.

A change like below should work instead.  Could you give it a try?


Takashi

-- 8< --
--- a/sound/core/sgbuf.c
+++ b/sound/core/sgbuf.c
@@ -108,7 +108,7 @@ void *snd_malloc_sgbuf_pages(struct device *device,
 			break;
 		}
 		chunk = tmpb.bytes >> PAGE_SHIFT;
-		for (i = 0; i < chunk; i++) {
+		for (i = 0; i < chunk && pages > 0; i++) {
 			table->buf = tmpb.area;
 			table->addr = tmpb.addr;
 			if (!i)
@@ -117,9 +117,9 @@ void *snd_malloc_sgbuf_pages(struct device *device,
 			*pgtable++ = virt_to_page(tmpb.area);
 			tmpb.area += PAGE_SIZE;
 			tmpb.addr += PAGE_SIZE;
+			sgbuf->pages++;
+			pages--;
 		}
-		sgbuf->pages += chunk;
-		pages -= chunk;
 		if (chunk < maxpages)
 			maxpages = chunk;
 	}