linux-ext4 - Re: [PATCH] ext4: avoid oversized shift in ext4_fill_flex

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Message-Id: <3C498AE4-D26A-41AD-A862-EE1C80290C7B@gmail.com>
Date:	Mon, 26 Dec 2011 21:26:22 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Andreas Dilger <aedilger@...il.com>
Cc:	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: avoid oversized shift in ext4_fill_flex_info()

On Dec 26, 2011, at 2:20 AM, Andreas Dilger wrote:
> While this is true in theory, it is not possible to have 2^32 groups per flex group. This would mean 2^32 block bitmaps and inode bitmaps in a single group, which is impossible. 

This patch is based on commit 503358ae "ext4: avoid divide by zero
when trying to mount a corrupted file system", as I quote: "If
s_log_groups_per_flex is greater than 31, then groups_per_flex will
will overflow and cause a divide by zero error."  The intent is to
avoid oversized shift in that commit, because the behavior is
undefined in C and may vary on different architectures.

My understanding is that sbi->s_es->s_log_groups_per_flex needs a
sanity check if it is read from a malicious or corrupted filesystem
in ext4_fill_flex_info(), which is called from ext4_fill_super().

Did I miss anything?

- xi--
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