ipv6: Fix dangling pointer when ipv6 fragment
BugLink: https://bugs.launchpad.net/bugs/1828420 [ Upstream commit ef0efcd3 ] 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: 405c92f7 ("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> Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com> Acked-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com> Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
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