From: Bob Copeland <me@bobcopeland.com>
To: Kees Cook <keescook@chromium.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>,
linux-karma-devel@lists.sourceforge.net,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH][next] fs: omfs: Use flexible-array member in struct omfs_extent
Date: Wed, 19 Jul 2023 09:03:29 -0400 [thread overview]
Message-ID: <ZLffIfEKz/nR9Jj/@bobcopeland.com> (raw)
In-Reply-To: <202307170758.14B5D83D@keescook>
On Mon, Jul 17, 2023 at 08:20:22AM -0700, Kees Cook wrote:
> > @@ -14,7 +14,7 @@ static u32 omfs_max_extents(struct omfs_sb_info *sbi, int offset)
> > {
> > return (sbi->s_sys_blocksize - offset -
> > sizeof(struct omfs_extent)) /
> > - sizeof(struct omfs_extent_entry) + 1;
> > + sizeof(struct omfs_extent_entry);
> > }
>
> I think the original calculation meant to do:
>
> return (sbi->s_sys_blocksize - offset -
> (sizeof(struct omfs_extent) - sizeof(struct omfs_extent_entry))) /
> sizeof(struct omfs_extent_entry);
I can confirm the intent. I also went back and looked at the usages just
to be sure.
In this case, there are two possible values for x = s_sys_blocksize - offset:
7728 or 8128, and both can be divided by 16 evenly so you have either:
f_old = (x - 32) / 16 + 1 or:
f_new = (x - 16) / 16
they both simplify to x/16 - 1 so they are equivalent for these inputs.
--
Bob Copeland %% https://bobcopeland.com/
prev parent reply other threads:[~2023-07-19 13:03 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-14 19:56 [PATCH][next] fs: omfs: Use flexible-array member in struct omfs_extent Gustavo A. R. Silva
2023-07-17 15:20 ` Kees Cook
2023-07-19 13:03 ` Bob Copeland [this message]
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