Summary

TCA_FLOWER_FLAGS (skip_hw/skip_sw) are encoded in big-endian via htonl, but netlink attributes are expected in native endian. On little-endian (x86) this flips the bits (e.g., 0x00000001 → 0x01000000), so skip_hw/skip_sw are not applied and tc flower filter add returns EINVAL or the flags are ignored. The tc CLI works because it encodes flags in native endian.

Details

• Affected: v1.3.1 and current master
• In filter_linux.go, encode does:

  var flags uint32
  if filter.SkipHw { flags |= nl.TCA_CLS_FLAGS_SKIP_HW }
  if filter.SkipSw { flags |= nl.TCA_CLS_FLAGS_SKIP_SW }
  parent.AddRtAttr(nl.TCA_FLOWER_FLAGS, htonl(flags)) // << big endian

• htonl in order.go uses binary.BigEndian
• TCA_FLOWER_FLAGS is NLA_U32 and should use native endian (like other u32 attrs via nl.Uint32Attr)

Reproduce

1. Create a Flower filter with SkipHw: true or SkipSw: true on x86
2. netlink.FilterAdd returns EINVAL or the flag is not applied (skip_hw/skip_sw missing)
3. Adding the same rule via tc CLI succeeds

Fix

- parent.AddRtAttr(nl.TCA_FLOWER_FLAGS, htonl(flags))
+ parent.AddRtAttr(nl.TCA_FLOWER_FLAGS, nl.Uint32Attr(flags))

Impact

With the fix, skip_hw/skip_sw are correctly set, matching tc CLI behavior; avoids EINVAL and ensures flower rules respect offload flags.