From: Andreas Dilger <adilger@clusterfs.com>
To: Can Sar <csar@stanford.edu>
Cc: linux-fsdevel@vger.kernel.org
Subject: Re: Divide by Zero in Linux 2.4.31 and 2.6.14
Date: Thu, 3 Nov 2005 11:08:07 -0700 [thread overview]
Message-ID: <20051103180807.GP31368@schatzie.adilger.int> (raw)
In-Reply-To: <B3EAECDC-5FB4-42E2-BB4D-3B8123D2F4A8@stanford.edu>
On Nov 03, 2005 05:03 -0800, Can Sar wrote:
> There is a bug in both ext2 and 3 that was fixed in 2.6.10 where if
> s_blocks_per_group (in the ext2_superblock) is 0 this will cause a
> division by zero. Unfortunately, this bug is still in 2.4.31.
>
> Furthermore, there is another bug where if s_inodes_per_group is 0 we
> again get a division by 0. This bug exists in both 2.6.14 and 2.4.31.
It is impossible to have an ext[23] filesystem with 0 blocks per group
or 0 inodes per group. That said, it seems that ext[23]_fill_super()
check for too large values and not zero, so a patch to verify these
values at mount would be OK.
> Finally, it seems that in the current implementation the EXT2/3 error
> mode that is set in the superblock cannot be overriden by the mount
> option if it is set to panic. This would mean that mounting a disk
> image with s_errors = 3 (EXT2_ERRORS_PANIC) and some false values in
> the superblock that are checked after s_errors is read will again
> cause a kernel panic. This is definitely the case in 2.4, and seems
> to be the case in 2.6 kernels as well though I haven't gotten around
> to trying that particular test case yet.
In ext3_fill_super() we do not call ext3_error() (only printk) so this
should not invoke panic() if there is an error during mount. The
ERRORS_PANIC flag is cleared in parse_options() if some other errors=
behaviour is set, so I can't see the sequence of events that would
lead to the situation you describe.
> I hope these bug reports help. We are still in the early stages of
> using our tool and hope to provide you with more bug reports in the
> future.
Always good to have such checking done.
Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.
prev parent reply other threads:[~2005-11-03 18:13 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-03 13:03 Divide by Zero in Linux 2.4.31 and 2.6.14 Can Sar
2005-11-03 18:08 ` Andreas Dilger [this message]
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