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fix(link): add missing BPF_F_REPLACE flag for RawAttachProgram #1995

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Merged
ti-mo merged 1 commit into from
May 13, 2026
+57 −3
Merged

fix(link): add missing BPF_F_REPLACE flag for RawAttachProgram #1995

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5 changes: 2 additions & 3 deletions link/program.go
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Original file line number Diff line number Diff line change
Expand Up @@ -50,12 +50,11 @@ func RawAttachProgram(opts RawAttachProgramOptions) error {
return fmt.Errorf("attach program: %w", err)
}

if flags == sys.BPF_F_REPLACE {
// Ensure that replacing a program works on old kernels.
attr.AttachFlags |= flags
if flags&sys.BPF_F_REPLACE != 0 {
attr.ReplaceBpfFd = fdOrID
} else {
attr.RelativeFdOrId = fdOrID
attr.AttachFlags |= flags
}
}

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55 changes: 55 additions & 0 deletions link/program_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ package link
import (
"fmt"
"net"
"os"
"testing"

"github.com/cilium/ebpf"
Expand Down Expand Up @@ -135,3 +136,57 @@ func TestRawAttachProgramAnchor(t *testing.T) {
})
qt.Assert(t, qt.IsNil(err))
}

func TestRawAttachProgramReplace(t *testing.T) {
testutils.SkipOnOldKernel(t, "5.9", "BPF_F_ALLOW_MULTI with BPF_F_REPLACE")

cgroup, progA := mustCgroupFixtures(t)

// Attach progA.
qt.Assert(t, qt.IsNil(RawAttachProgram(RawAttachProgramOptions{
Target: int(cgroup.Fd()),
Program: progA,
Attach: ebpf.AttachCGroupInetEgress,
Flags: uint32(flagAllowMulti),
})))

// Replace progA with progB. BPF_F_ALLOW_MULTI must be passed again when
// replacing a program that was originally attached with that flag.
progB := mustLoadProgram(t, ebpf.CGroupSKB, ebpf.AttachCGroupInetEgress, "")
qt.Assert(t, qt.IsNil(RawAttachProgram(RawAttachProgramOptions{
Target: int(cgroup.Fd()),
Program: progB,
Attach: ebpf.AttachCGroupInetEgress,
Flags: uint32(flagAllowMulti),
Anchor: ReplaceProgram(progA),
})))
t.Cleanup(func() {
qt.Assert(t, qt.IsNil(RawDetachProgram(RawDetachProgramOptions{
Target: int(cgroup.Fd()),
Program: progB,
Attach: ebpf.AttachCGroupInetEgress,
Flags: uint32(flagAllowMulti),
})))
})

progBInfo, err := progB.Info()
qt.Assert(t, qt.IsNil(err))
progBID, _ := progBInfo.ID()

// Query attached programs and verify only progB is present.
result, err := QueryPrograms(QueryOptions{
Target: int(cgroup.Fd()),
Attach: ebpf.AttachCGroupInetEgress,
})
qt.Assert(t, qt.IsNil(err))
qt.Assert(t, qt.HasLen(result.Programs, 1))
qt.Assert(t, qt.Equals(result.Programs[0].ID, progBID))

// progA should fail to detach.
qt.Assert(t, qt.ErrorIs(RawDetachProgram(RawDetachProgramOptions{
Target: int(cgroup.Fd()),
Program: progA,
Attach: ebpf.AttachCGroupInetEgress,
Flags: uint32(flagAllowMulti),
}), os.ErrNotExist))
}
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