From: Kees Cook <keescook@xxxxxxxxxxxx> [ Upstream commit 7cba18332e3635aaae60e4e7d4e52849de50d91b ] 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@xxxxxxxxxxxx Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx> Cc: Jiri Pirko <jiri@xxxxxxxxxxx> Reported-by: syzbot+a2c4601efc75848ba321@xxxxxxxxxxxxxxxxxxxxxxxxx Link: https://lore.kernel.org/lkml/000000000000a96c0b05e97f0444@xxxxxxxxxx/ Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220927153700.3071688-1-keescook@xxxxxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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; -- 2.35.1
