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Date: Fri, 28 Oct 2022 21:07:52 -0700 From: Eric Dumazet <edumazet@...gle.com> To: Ziyang Xuan <william.xuanziyang@...wei.com> Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, peterpenkov96@...il.com, maheshb@...gle.com, ast@...nel.org, daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com Subject: Re: [PATCH net] net: tun: fix bugs for oversize packet when napi frags enabled On Fri, Oct 28, 2022 at 8:32 PM Ziyang Xuan <william.xuanziyang@...wei.com> wrote: > > Recently, we got two syzkaller problems because of oversize packet > when napi frags enabled. > > One of the problems is because the first seg size of the iov_iter > from user space is very big, it is 2147479538 which is bigger than > the threshold value for bail out early in __alloc_pages(). And > skb->pfmemalloc is true, __kmalloc_reserve() would use pfmemalloc > reserves without __GFP_NOWARN flag. Thus we got a warning as following: > > ======================================================== > > Restrict the packet size less than ETH_MAX_MTU to fix the problems. > Add len check in tun_napi_alloc_frags() simply. Athough that makes > some kinds of packets payload size slightly smaller than the length > allowed by the protocol, for example, ETH_HLEN + sizeof(struct ipv6hdr) > smaller when the tun device type is IFF_TAP and the packet is IPv6. But > I think that the effect is small and can be ignored. I am not sure about ETH_MAX_MTU being completely safe. napi_get_frags() / napi_alloc_skb() is reserving NET_SKB_PAD + NET_IP_ALIGN bytes. transport_header being an offset from skb->head, we probably want to use (ETH_MAX_MTU - NET_SKB_PAD - NET_IP_ALIGN) My objection to your initial patch was that you were using PAGE_SIZE, while Ethernet MTU can easily be ~9000 But 0xFFFF is a bit too much/risky. Thanks. > > Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") > Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com> > --- > drivers/net/tun.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 27c6d235cbda..98d3160fcae2 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -1459,7 +1459,7 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile, > int err; > int i; > > - if (it->nr_segs > MAX_SKB_FRAGS + 1) > + if (it->nr_segs > MAX_SKB_FRAGS + 1 || len > ETH_MAX_MTU) > return ERR_PTR(-EMSGSIZE); > > local_bh_disable(); > -- > 2.25.1 >
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