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Message-ID: <44e8dcf8-bf64-0407-65bb-122d0853c672@huawei.com> Date: Tue, 2 Apr 2019 11:09:28 +0800 From: hujunwei <hujunwei4@...wei.com> To: <davem@...emloft.net>, <kuznet@....inr.ac.ru>, <yoshfuji@...ux-ipv6.org>, <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org> CC: <mingfangsen@...wei.com>, <liuzhiqiang26@...wei.com>, <zhangwenhao8@...wei.com>, <wangxiaogang3@...wei.com> Subject: [PATCH v3 net] ipv6: Fix dangling pointer when ipv6 fragment From: Junwei Hu <hujunwei4@...wei.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@...wei.com> Reported-by: Wenhao Zhang <zhangwenhao8@...wei.com> Reported-by: syzbot+e8ce541d095e486074fc@...kaller.appspotmail.com Reviewed-by: Zhiqiang Liu <liuzhiqiang26@...wei.com> Acked-by: Martin KaFai Lau <kafai@...com> --- V2->V3: - fix patch format issue - add Acked-by net/ipv6/ip6_output.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index edbd12067170..533be3268e52 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -601,11 +601,12 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, inet6_sk(skb->sk) : NULL; struct ipv6hdr *tmp_hdr; struct frag_hdr *fh; - unsigned int mtu, hlen, left, len; + unsigned int mtu, hlen, left, len, nexthdr_offset; int hroom, troom; __be32 frag_id; int ptr, offset = 0, err = 0; u8 *prevhdr, nexthdr = 0; + nexthdr_offset = prevhdr - skb_network_header(skb); err = ip6_find_1stfragopt(skb, &prevhdr); if (err < 0) @@ -646,6 +647,7 @@ 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); -- 2.19.1
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