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Message-ID: <CAM0EoM=fZVr4ROKZ+tA9A=yxcx6LnNVFzTb+_brFv9c-CiRfdA@mail.gmail.com> 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
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