Introduction:
Crafting custom DHCP responses requires the ability to specify the source IP address, a feature not readily accessible within the standard Go networking library. This article explores the challenges and solutions involved in using raw sockets in Go to overcome this limitation.
Security Implications:
Spoofing the source IP address of a DHCP packet possesses serious security risks. Consequently, elevated privileges or special capabilities are essential for forging packets with custom headers in Linux environments.
Raw Sockets in Go:
The net package lacks raw socket functionality due to its specialized nature. However, the go.net subrepository provides the necessary modules:
Header Spoofing:
To manipulate the DHCP headers, it is crucial to utilize ipv4.RawConn's ReadFrom method for reading the original packet. The following code snippet demonstrates how to set up the headers for the subsequent WriteTo call:
<code class="go">for { hdr, payload, _, err := conn.ReadFrom(buf) if err != nil { ... } hdr.ID = 0 hdr.Checksum = 0 hdr.Src = ... /* Address derived from GIADDR */ hdr.Dst = ... /* Destination address */ if err := conn.WriteTo(hdr, payload, nil); err != nil { ... } }</code>
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