Fix link-layer address enumeration on macOS

[wfurt]

Fixes #125711

Summary

• expand the native and managed link-layer address buffers from 8 to 12 bytes
• clamp the copied address length to the reported source record and destination capacity
• use the fixed sdl_data capacity on SunOS, where sockaddr_dl does not expose sdl_len
• add native compile-time assertions for the interop buffer layout

The hardware-specific scenario requires a special link-layer adapter and was not reproduced locally. The bounds and layouts were validated through native compilation, the existing macOS interface enumeration tests, and specialist review.

Testing

• ./build.sh libs.native
• ./dotnet.sh build /t:test src/libraries/System.Net.NetworkInformation/tests/FunctionalTests/System.Net.NetworkInformation.Functional.Tests.csproj (246 passed)

Note

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[Copilot]

Pull request overview

This PR updates the Unix System.Native interface-address enumeration and its managed interop to safely handle link-layer (AF_LINK / sockaddr_dl) addresses that can exceed the previously assumed 8-byte buffer, particularly on macOS.

Changes:

• Expand link-layer address storage in native PAL structs and managed interop structs from 8 to 12 bytes.
• Clamp the link-layer address copy length to both the source record’s reported capacity and the destination buffer size (including a SunOS-specific path where sdl_len isn’t available).
• Add native compile-time assertions to validate the interop struct layout assumptions.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/native/libs/System.Native/pal_interfaceaddresses.h	Expands native struct link-layer address buffers to 12 bytes.
src/native/libs/System.Native/pal_interfaceaddresses.c	Adds length-clamping helper for AF_LINK and updates copies + adds layout assertions.
src/libraries/Common/src/Interop/Unix/System.Native/Interop.EnumerateInterfaceAddresses.cs	Updates managed interop structs to match the new 12-byte native buffers.

Suppressed comments (1)

src/native/libs/System.Native/pal_interfaceaddresses.c:471

• Same as above: LLADDR(sadl) is computed even when NumAddressBytes clamps to 0. Guarding the copy avoids forming a potentially out-of-bounds pointer for malformed/short records.

            memcpy_s(&nii->AddressBytes, sizeof_member(NetworkInterfaceInfo, AddressBytes), (uint8_t*)LLADDR(sadl), nii->NumAddressBytes);

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.