From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: Len Baker <len.baker@gmx.com>, Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] writeback: prefer struct_size over open coded arithmetic
Date: Mon, 20 Sep 2021 19:17:36 -0500 [thread overview]
Message-ID: <6bc45138-c3a5-9465-40cb-3db714e7706d@embeddedor.com> (raw)
In-Reply-To: <20210919094630.30668-1-len.baker@gmx.com>
On 9/19/21 04:46, Len Baker wrote:
> As noted in the "Deprecated Interfaces, Language Features, Attributes,
> and Conventions" documentation [1], size calculations (especially
> multiplication) should not be performed in memory allocator (or similar)
> function arguments due to the risk of them overflowing. This could lead
> to values wrapping around and a smaller allocation being made than the
> caller was expecting. Using those allocations could lead to linear
> overflows of heap memory and other misbehaviors.
>
> In this case this is not actually dynamic size: all the operands
> involved in the calculation are constant values. However it is best to
> refactor this anyway, just to keep the open-coded math idiom out of
> code.
>
> So, use the struct_size() helper to do the arithmetic instead of the
> argument "size + count * size" in the kzalloc() function.
>
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
>
> Signed-off-by: Len Baker <len.baker@gmx.com>
> ---
> fs/fs-writeback.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 81ec192ce067..f7abff31e026 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -624,8 +624,8 @@ bool cleanup_offline_cgwb(struct bdi_writeback *wb)
> int nr;
> bool restart = false;
>
> - isw = kzalloc(sizeof(*isw) + WB_MAX_INODES_PER_ISW *
> - sizeof(struct inode *), GFP_KERNEL);
> + isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW),
> + GFP_KERNEL);
There is another instance at:
569 isw = kzalloc(sizeof(*isw) + 2 * sizeof(struct inode *), GFP_ATOMIC);
570 if (!isw)
571 return;
If you are finding these with the help of Coccinelle, please mention it
in the changelog text. :)
Thanks
--
Gustavo
> if (!isw)
> return restart;
>
> --
> 2.25.1
>
prev parent reply other threads:[~2021-09-21 0:40 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-19 9:46 [PATCH] writeback: prefer struct_size over open coded arithmetic Len Baker
2021-09-21 0:17 ` Gustavo A. R. Silva [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=6bc45138-c3a5-9465-40cb-3db714e7706d@embeddedor.com \
--to=gustavo@embeddedor.com \
--cc=gustavoars@kernel.org \
--cc=keescook@chromium.org \
--cc=len.baker@gmx.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).