Re: [PATCH] ext4: avoid oversized shift in ext4_fill_flex_info()

[Xi Wang <xi.wang@gmail.com>]

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