netdev - Re: [PATCH][next] net: sched: cls_u32: Fix allocation in u32

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Mon, 21 Aug 2023 10:35:29 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>, Cong Wang <xiyou.wangcong@...il.com>, 
	Jiri Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] net: sched: cls_u32: Fix allocation in u32_init()

On Fri, Aug 18, 2023 at 10:38 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 17 Aug 2023 09:58:53 -0600 Gustavo A. R. Silva wrote:
> > Subject: [PATCH][next] net: sched: cls_u32: Fix allocation in u32_init()
> > Date: Thu, 17 Aug 2023 09:58:53 -0600
> >
> > Replace struct_size() with sizeof(), and avoid allocating 8 too many
> > bytes.
>
> What are you fixing?
>
> > The following difference in binary output is expected and reflects the
> > desired change:
> >
> > | net/sched/cls_u32.o
> > | @@ -6148,7 +6148,7 @@
> > | include/linux/slab.h:599
> > |     2cf5:      mov    0x0(%rip),%rdi        # 2cfc <u32_init+0xfc>
> > |                        2cf8: R_X86_64_PC32     kmalloc_caches+0xc
> > |-    2cfc:      mov    $0x98,%edx
> > |+    2cfc:      mov    $0x90,%edx
>
> Sure, but why are you doing this? And how do you know the change is
> correct?
>
> There are 2 other instances where we allocate 1 entry or +1 entry.
> Are they not all wrong?
>
> Also some walking code seems to walk <= divisor, divisor IIUC being
> the array bound - 1?
>
> Jamal acked so changes are this is right, but I'd really like to
> understand what's going on, and I shouldn't have to ask you all
> these questions :S

This is a "bug fix" given that the structure had no zero array
construct as was implied by d61491a51f7e . I didnt want to call it out
as a bug fix (for -net) because existing code was not harmful but
allocated extra memory which this patch gives back.
The other instances have a legit need for "flexible array".

cheers,
jamal
> --
> pw-bot: cr