fix: agent - eBPF Fix TCP DNS client request loss #9218
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Note that TCP DNS adds two length bytes at the beginning of the protocol, whereas UDP DNS does not. We need to handle this properly to ensure that these two length bytes are not sent to the upper layer. When receiving data, the client does not first receive two bytes but instead receives everything at once; whereas the server receives two bytes (length) first and then receives the remaining bytes. When the client sends a request, it combines both 'A' and 'AAAA' type queries into a single request to the CoreDNS server. The first two bytes represent the length, but this length only includes the 'A' query, not the combined length of both the 'A' and 'AAAA' queries (the total size is referred to as "count" here). As a result, the length check may miss this case. This fixes the issue where the client fails to retrieve the request by adding direction judgment.
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下面是客户端 wrk:worker_0 和服务端 coredns 的DNS通信行为。
双记录查询：客户端同时发送A和AAAA记录请求，是支持IPv4/IPv6双栈环境的典型行为（如Pod网络配置为双栈模式）。
服务端先收取 A 记录(上面)的查询信息进行应答：
应答记录 服务端再收取 AAAA 查询进行应答：
客户端接收(A的应答，注意它没有先读取4字节)：
客户端接收( |
sharang
approved these changes
Feb 28, 2025
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Note that TCP DNS adds two length bytes at the beginning of the protocol, whereas UDP DNS does not. We need to handle this properly to ensure that these two length bytes are not sent to the upper layer.
When receiving data, the client does not first receive two bytes but instead receives everything at once; whereas the server receives two bytes (length) first and then receives the remaining bytes.
When the client sends a request, it combines both 'A' and 'AAAA' type queries into a single request to the CoreDNS server. The first two bytes represent the length, but this length only includes the 'A' query, not the combined length of both the 'A' and 'AAAA' queries (the total size is referred to as "count" here). As a result, the length check may miss this case.
This fixes the issue where the client fails to retrieve the request by adding direction judgment.
This PR is for:
Affected branches