kern/144732: [patch] geom_cache erroneously decodes its on-disk label

Eugene Grosbein eugen at grosbein.pp.ru
Sun Mar 14 11:30:08 UTC 2010


>Number:         144732
>Category:       kern
>Synopsis:       [patch] geom_cache erroneously decodes its on-disk label
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Mar 14 11:30:05 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Eugene Grosbein
>Release:        FreeBSD 8.0-STABLE i386
>Organization:
RDTC JSC
>Environment:
System: FreeBSD grosbein.pp.ru 8.0-STABLE FreeBSD 8.0-STABLE #11: Sat Feb 6 21:23:34 KRAT 2010 root at grosbein.pp.ru:/usr/local/obj/usr/local/src/sys/DADV i386

>Description:

	Let's take a look at struct g_cache_metadata definition in
	/usr/src/sys/geom/cache/g_cache.h:

struct g_cache_metadata {
        char            md_magic[16];           /* Magic value. */
        uint32_t        md_version;             /* Version number. */
        char            md_name[16];            /* Cache value. */
        uint32_t        md_bsize;               /* Cache block size. */
        uint32_t        md_size;                /* Cache size. */
        uint64_t        md_provsize;            /* Provider's size. */
};

	Note that md_size is 32-bit unsigned value. Next lines present
	cache_metadata_encode() funtion that uses le32enc() to encode
	this value, that's right.

	Now look at cache_metadata_decode() below: it uses le16dec()
	function to decode stored label. This error effectively limits
	cache size to 16-bit quantity (and limits stripe/block size too).

>How-To-Repeat:

	kldload geom_cache
	gcache label -v -b 32768 -s 65536

	Label is written successfully but gem_cache compains to kernel log:

GEOM_CACHE: Invalid size for device ca0.

	That's because le16dec() decodes 65536 as zero cache size.

>Fix:

--- sys/geom/cache/g_cache.h.orig	2010-03-14 17:36:16.000000000 +0700
+++ sys/geom/cache/g_cache.h	2010-03-14 17:35:25.000000000 +0700
@@ -139,7 +139,7 @@
 	md->md_version = le32dec(data + 16);
 	bcopy(data + 20, md->md_name, sizeof(md->md_name));
 	md->md_bsize = le32dec(data + 36);
-	md->md_size = le16dec(data + 40);
+	md->md_size = le32dec(data + 40);
 	md->md_provsize = le64dec(data + 44);
 }
 


>Release-Note:
>Audit-Trail:
>Unformatted:


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