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Bug
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Resolution: Unresolved
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Medium
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None
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None
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None
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OS: Ubuntu 22.04 (x86_64)
When NAT client using ICMP echo method to do traceroute after enable nat44 plugin, the TTL exceeded error packet got the wrong checksum.
After some debugging, I found that at `src/plugins/nat/nat44-ed/nat44_ed.c:3946 to 3961` , when updating checksum, nat44 only updates the inner and outer ICMP header checksum for ICMP ID but forgot to also update the outer ICMP checksum again after the inner ICMP checksum is changed.
if (f->rewrite.icmp_id != inner_echo->identifier)
{
ip_csum_t sum = icmp->checksum;
sum = ip_csum_update (sum, inner_echo->identifier,
f->rewrite.icmp_id,
nat_icmp_echo_header_t,
identifier /* changed member */);
icmp->checksum = ip_csum_fold (sum);
ip_csum_t inner_sum = inner_icmp->checksum;
inner_sum = ip_csum_update (
sum, inner_echo->identifier, f->rewrite.icmp_id,
nat_icmp_echo_header_t,
identifier /* changed member */);
inner_icmp->checksum = ip_csum_fold (inner_sum);
inner_echo->identifier = f->rewrite.icmp_id;
}
The problem is temporarily fixed after I add this snippet of code.
if (f->rewrite.icmp_id != inner_echo->identifier)
{
ip_csum_t sum = icmp->checksum;
sum = ip_csum_update (sum, inner_echo->identifier,
f->rewrite.icmp_id,
nat_icmp_echo_header_t,
identifier /* changed member */);
icmp->checksum = ip_csum_fold (sum);
ip_csum_t inner_sum = inner_icmp->checksum;
inner_sum = ip_csum_update (
sum, inner_echo->identifier, f->rewrite.icmp_id,
nat_icmp_echo_header_t,
identifier /* changed member */);
+ sum = icmp->checksum;
+ sum = ip_csum_update(sum, inner_icmp->checksum,
+ ip_csum_fold(inner_sum),
+ icmp46_header_t,
+ checksum);
+ icmp->checksum = ip_csum_fold (sum);
inner_icmp->checksum = ip_csum_fold (inner_sum);
inner_echo->identifier = f->rewrite.icmp_id;
}
How to reproduce
VPP script
nat44 plugin enable nat44 forwarding enable nat44 add interface address <wan interface> set int nat44 out <wan interface> output-feature
NAT client
traceroute -I www.google.com
