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Message-Id: <20220927153700.3071688-1-keescook@chromium.org> Date: Tue, 27 Sep 2022 08:37:01 -0700 From: Kees Cook <keescook@...omium.org> To: Jamal Hadi Salim <jhs@...atatu.com> Cc: Kees Cook <keescook@...omium.org>, Eric Dumazet <edumazet@...gle.com>, Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, syzbot+a2c4601efc75848ba321@...kaller.appspotmail.com, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: [PATCH] net: sched: cls_u32: Avoid memcpy() false-positive warning To work around a misbehavior of the compiler's ability to see into composite flexible array structs (as detailed in the coming memcpy() hardening series[1]), use unsafe_memcpy(), as the sizing, bounds-checking, and allocation are all very tightly coupled here. This silences the false-positive reported by syzbot: memcpy: detected field-spanning write (size 80) of single field "&n->sel" at net/sched/cls_u32.c:1043 (size 16) [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org Cc: Jamal Hadi Salim <jhs@...atatu.com> Cc: Eric Dumazet <edumazet@...gle.com> Cc: Cong Wang <xiyou.wangcong@...il.com> Cc: Jiri Pirko <jiri@...nulli.us> Cc: "David S. Miller" <davem@...emloft.net> Cc: Jakub Kicinski <kuba@...nel.org> Cc: Paolo Abeni <pabeni@...hat.com> Cc: netdev@...r.kernel.org Reported-by: syzbot+a2c4601efc75848ba321@...kaller.appspotmail.com Link: https://lore.kernel.org/lkml/000000000000a96c0b05e97f0444@google.com/ Signed-off-by: Kees Cook <keescook@...omium.org> --- net/sched/cls_u32.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c index 4d27300c287c..5f33472aad36 100644 --- a/net/sched/cls_u32.c +++ b/net/sched/cls_u32.c @@ -1040,7 +1040,11 @@ 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 with struct_size(), + * bounds-checked against nla_len(), and allocated + * above. */); RCU_INIT_POINTER(n->ht_up, ht); n->handle = handle; n->fshift = s->hmask ? ffs(ntohl(s->hmask)) - 1 : 0; -- 2.34.1
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