linux-kernel - Re: [PATCH 2.4] FAT: do not continue in fat_get

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Message-ID: <20100203101449.2090aa57@strolchi>
Date:	Wed, 3 Feb 2010 10:14:49 +0100
From:	Stefan Seyfried <stefan.seyfried@...glemail.com>
To:	Willy Tarreau <w@....eu>
Cc:	linux-kernel@...r.kernel.org, Stefan Seyfried <seife@...airon.com>
Subject: Re: [PATCH 2.4] FAT: do not continue in fat_get_block if bmap fails

Hi Willy,

On Tue, 2 Feb 2010 23:06:31 +0100
Willy Tarreau <w@....eu> wrote:

> Hello Stefan,
> 
> On Tue, Feb 02, 2010 at 02:00:35PM +0100, Stefan Seyfried wrote:
> > From: Stefan Seyfried <seife@...airon.com>
> > 
> > There is no use in continuing the write operation after fat_bmap() fails.
> > (This successfully killed a VFAT FS for me).
> > The corresponding code in 2.6 does return here as well, AFAICT.
> 
> OK then that's fine, I'm merging it.

I'd like to add that I am not a filesystem expert at all, so if
somebody wants to suggest a better return code, I'm all for that.

And the dosfs code in 2.6 is substantially different, thus the "AFAICT"
above ;)

Anyway, continuing at that place (when phys == 0) is definitely
wrong, since writing to block 0 later on will kill the filesystem 100%.

I triggered this with a corrumpted file, which an application wanted to
modify, dosfsck had this to say about the file system:

strolchi:~ # dosfsck -nv /dev/sdb1
dosfsck 2.11 (12 Mar 2005)
dosfsck 2.11, 12 Mar 2005, FAT32, LFN
Checking we can access the last sector of the filesystem
Boot sector contents:
System ID "MSDOS5.0"
Media byte 0xf8 (hard disk)
       512 bytes per logical sector
     16384 bytes per cluster
         1 reserved sector
First FAT starts at byte 512 (sector 1)
         2 FATs, 16 bit entries
    124928 bytes per FAT (= 244 sectors)
Root directory starts at byte 250368 (sector 489)
       512 root directory entries
Data area starts at byte 266752 (sector 521)
     62283 data clusters (1020444672 bytes)
63 sectors/track, 32 heads
       247 hidden sectors
   1993577 sectors total
/test/test.db
  File size is 188928 bytes, cluster chain length is 163840 bytes.
  Truncating file to 163840 bytes.
Checking for unused clusters.
Reclaimed 2 unused clusters (32768 bytes).
Leaving file system unchanged.
/dev/sdb1: 201 files, 51608/62283 clusters

Thanks for merging and taking care of the "old lady" 2.4 ;)

	Stefan
-- 
Stefan Seyfried

"Any ideas, John?"
"Well, surrounding them's out."
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