Attachment 174080 Details for Bug 212139 – Prevent read-ahead from crossing 32 bit aliases of end-of-disk

[patch] Prevent read-ahead from crossing 32 bit aliases of end-of-disk

p (text/plain), 1.14 KB, created by Peter Wemm on 2016-08-25 22:18:20 UTC

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Creator: Peter Wemm

Created: 2016-08-25 22:18:20 UTC

Size: 1.14 KB

patch

obsolete

>Index: biosdisk.c
>===================================================================
>--- biosdisk.c	(revision 304792)
>+++ biosdisk.c	(working copy)
>@@ -497,7 +497,7 @@
>     char *buf, size_t *rsize)
> {
>     struct disk_devdesc *dev = (struct disk_devdesc *)devdata;
>-    int			blks;
>+    int			blks, remaining;
> #ifdef BD_SUPPORT_FRAGS /* XXX: sector size */
>     char		fragbuf[BIOSDISK_SECSIZE];
>     size_t		fragsize;
>@@ -513,14 +513,15 @@
>     if (rsize)
> 	*rsize = 0;
> 
>-    if (dblk >= BD(dev).bd_sectors) {
>-	DEBUG("IO past disk end %llu", (unsigned long long)dblk);
>-	return (EIO);
>-    }
>-
>-    if (dblk + blks > BD(dev).bd_sectors) {
>-	/* perform partial read */
>-	blks = BD(dev).bd_sectors - dblk;
>+    /*
>+     * Perform partial read to prevent read-ahead crossing
>+     * the end of disk - or any 32 bit aliases of the end.
>+     * Signed arithmetic is used to handle wrap-around cases
>+     * like we do for TCP sequence numbers.
>+     */
>+    remaining = (int)(BD(dev).bd_sectors - dblk);	/* truncate */
>+    if (remaining > 0 && remaining < blks) {
>+	blks = remaining;
> 	size = blks * BD(dev).bd_sectorsize;
> 	DEBUG("short read %d", blks);
>     }

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Attachments on bug 212139: 174052 | 174075 | 174080