From: Kees Cook keescook@chromium.org
[ 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@ch...
Cc: Cong Wang xiyou.wangcong@gmail.com Cc: Jiri Pirko jiri@resnulli.us Reported-by: syzbot+a2c4601efc75848ba321@syzkaller.appspotmail.com Link: https://lore.kernel.org/lkml/000000000000a96c0b05e97f0444@google.com/ Signed-off-by: Kees Cook keescook@chromium.org Reviewed-by: Jamal Hadi Salim jhs@mojatatu.com Link: https://lore.kernel.org/r/20220927153700.3071688-1-keescook@chromium.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.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;