On Sat, Apr 10, 2021 at 01:00:34PM +0200, Eric Dumazet wrote: > On Sat, Apr 10, 2021 at 12:12 PM Eric Dumazet <eduma...@google.com> wrote: > > > > On Sat, Apr 10, 2021 at 11:51 AM Phillip Potter <p...@philpotter.co.uk> > > wrote: > > > > > > Zero-fill skb->data in __alloc_skb function of net/core/skbuff.c, > > > up to start of struct skb_shared_info bytes. Fixes a KMSAN-found > > > uninit-value bug reported by syzbot at: > > > https://syzkaller.appspot.com/bug?id=abe95dc3e3e9667fc23b8d81f29ecad95c6f106f > > > > > > Reported-by: syzbot+2e406a9ac75bb71d4...@syzkaller.appspotmail.com > > > Signed-off-by: Phillip Potter <p...@philpotter.co.uk> > > > --- > > > net/core/skbuff.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > > index 785daff48030..9ac26cdb5417 100644 > > > --- a/net/core/skbuff.c > > > +++ b/net/core/skbuff.c > > > @@ -215,6 +215,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t > > > gfp_mask, > > > * to allow max possible filling before reallocation. > > > */ > > > size = SKB_WITH_OVERHEAD(ksize(data)); > > > + memset(data, 0, size); > > > prefetchw(data + size); > > > > > > Certainly not. > > > > There is a difference between kmalloc() and kzalloc() > > > > Here you are basically silencing KMSAN and make it useless. > > > > Please fix the real issue, or stop using KMSAN if it bothers you. > > My understanding of the KMSAN bug (when I released it months ago) was > that it was triggered by some invalid assumptions in geneve_xmit() > > The syzbot repro sends a packet with a very small size (Ethernet > header only) and no IP/IPv6 header > > Fix for ipv4 part (sorry, not much time during week end to test all this) > > diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c > index > e3b2375ac5eb55f544bbc1f309886cc9be189fd1..0a72779bc74bc50c20c34c05b2c525cca829f33c > 100644 > --- a/drivers/net/geneve.c > +++ b/drivers/net/geneve.c > @@ -892,6 +892,9 @@ static int geneve_xmit_skb(struct sk_buff *skb, > struct net_device *dev, > __be16 sport; > int err; > > + if (!pskb_network_may_pull(skb, sizeof(struct iphdr)) > + return -EINVAL; > + > sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true); > rt = geneve_get_v4_rt(skb, dev, gs4, &fl4, info, > geneve->cfg.info.key.tp_dst, sport);
Dear Eric, Thank you for your help/feedback. I have crafted a patch using your code above and the equivalent check for geneve6_xmit_skb, and this works for me on my local KMSAN build. I am also running it through syzbot to check there as well. I will send out with appropriate attribution assuming all is OK on the testing front. Regards, Phil
