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Message-ID: <CAM0EoMm91Gmt6M7AVqp+OKvTH0Y0vCxQzpLndhwHzE-tke7J3g@mail.gmail.com> Date: Tue, 27 Sep 2022 07:23:29 -0400 From: Jamal Hadi Salim <jhs@...atatu.com> To: Kees Cook <keescook@...omium.org> Cc: Eric Dumazet <edumazet@...gle.com>, syzbot <syzbot+a2c4601efc75848ba321@...kaller.appspotmail.com>, David Miller <davem@...emloft.net>, Jiri Pirko <jiri@...nulli.us>, Jakub Kicinski <kuba@...nel.org>, LKML <linux-kernel@...r.kernel.org>, netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>, syzkaller-bugs <syzkaller-bugs@...glegroups.com>, Cong Wang <xiyou.wangcong@...il.com> Subject: Re: [syzbot] WARNING in u32_change Do you want to submit that patch then? FWIW, I could not recreate what syzbot saw even after setting CONFIG_FORTIFY_SOURCE=y cheers, jamal On Sun, Sep 25, 2022 at 10:39 PM Kees Cook <keescook@...omium.org> wrote: > > On Sun, Sep 25, 2022 at 10:34:37AM -0700, Eric Dumazet wrote: > > Sure, please look at: > > > > commit 54d9469bc515dc5fcbc20eecbe19cea868b70d68 > > Author: Kees Cook <keescook@...omium.org> > > Date: Thu Jun 24 15:39:26 2021 -0700 > > > > fortify: Add run-time WARN for cross-field memcpy() > > [...] > > Here, we might switch to unsafe_memcpy() instead of memcpy() > > I would tend to agree. Something like: > > diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c > index 4d27300c287c..21e0e6206ecc 100644 > --- a/net/sched/cls_u32.c > +++ b/net/sched/cls_u32.c > @@ -1040,7 +1040,9 @@ static int u32_change(struct net *net, struct sk_buff *in_skb, > } > #endif > > - memcpy(&n->sel, s, sel_size); > + unsafe_memcpy(&n->sel, s, sel_size, > + /* A composite flex-array structure destination, > + * which was correctly sized and allocated above. */); > RCU_INIT_POINTER(n->ht_up, ht); > n->handle = handle; > n->fshift = s->hmask ? ffs(ntohl(s->hmask)) - 1 : 0; > > This alloc/partial-copy pattern is relatively common in the kernel, so > I've been considering adding a helper for it. It'd be like kmemdup(), > but more like kmemdup_offset(), which only the object from a certainly > point is copied. > > -- > Kees Cook
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