Messages in this thread Patch in this message | | | Subject | Re: [PATCH net] ipv6: Fix dangling pointer when ipv6 fragment | From | Eric Dumazet <> | Date | Sat, 30 Mar 2019 00:48:06 -0700 |
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On 03/30/2019 12:29 AM, hujunwei wrote: > From: Junwei Hu <hujunwei4@huawei.com> > > At the beginning of ip6_fragment func, the prevhdr pointer is > obtained in the ip6_find_1stfragopt func. > However, all the pointers pointing into skb header may change > when calling skb_checksum_help func with > skb->ip_summed = CHECKSUM_PARTIAL condition. > The prevhdr pointe will be dangling if it is not reloaded after > calling __skb_linearize func in skb_checksum_help func. > > Here, I add a variable, nexthdr_offset, to evaluate the offset, > which does not changes even after calling __skb_linearize func. > > Fixes: 405c92f7a541 ("ipv6: add defensive check for CHECKSUM_PARTIAL skbs in ip_fragment") > Signed-off-by: Junwei Hu <hujunwei4@huawei.com> > Reported-by: Wenhao Zhang <zhangwenhao8@huawei.com> > Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Interesting.
We got a syzbot report yesterday about this issue. (email thread : BUG: unable to handle kernel paging request in ip6_fragment)
<quote> syzbot found the following crash on:
HEAD commit: 8c838f53 dpaa2-eth: fix race condition with bql frame acco.. git tree: net console output: https://syzkaller.appspot.com/x/log.txt?x=12b83a9b200000 kernel config: https://syzkaller.appspot.com/x/.config?x=f05902bca21d8935 dashboard link: https://syzkaller.appspot.com/bug?extid=e8ce541d095e486074fc compiler: gcc (GCC) 9.0.0 20181231 (experimental)
Unfortunately, I don't have any reproducer for this crash yet.
IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com </quote>
> > --- > net/ipv6/ip6_output.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c > index edbd12067170..6db3c60b3b66 100644 > --- a/net/ipv6/ip6_output.c > +++ b/net/ipv6/ip6_output.c > @@ -606,12 +606,14 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, > __be32 frag_id; > int ptr, offset = 0, err = 0; > u8 *prevhdr, nexthdr = 0; > + u8 nexthdr_offset; > > err = ip6_find_1stfragopt(skb, &prevhdr); > if (err < 0) > goto fail; > hlen = err; > nexthdr = *prevhdr; > + nexthdr_offset = prevhdr - skb_network_header(skb); > > mtu = ip6_skb_dst_mtu(skb); > > @@ -646,6 +648,8 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, > (err = skb_checksum_help(skb))) > goto fail; > > + prevhdr = skb_network_header(skb) + nexthdr_offset; > + > hroom = LL_RESERVED_SPACE(rt->dst.dev); > if (skb_has_frag_list(skb)) { > unsigned int first_len = skb_pagelen(skb); >
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