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Initialize ICMP echo ID and sequence to random values #412

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Jan 30, 2019
Merged

Initialize ICMP echo ID and sequence to random values #412

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20 changes: 19 additions & 1 deletion prober/icmp.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ package prober
import (
"bytes"
"context"
"math/rand"
"net"
"os"
"sync"
Expand All @@ -32,10 +33,27 @@ import (
)

var (
icmpID int
icmpSequence uint16
icmpSequenceMutex sync.Mutex
)

func init() {
// PID is typically 1 when running in a container; in that case, set
// the ICMP echo ID to a random value to avoid potential clashes with
// other blackbox_exporter instances. See #411.
if pid := os.Getpid(); pid == 1 {
icmpID = rand.Intn(1 << 16)
} else {
icmpID = pid & 0xffff
}

// Start the ICMP echo sequence at a random offset to prevent them from
// being in sync when several blackbox_exporter instances are restarted
// at the same time. See #411.
icmpSequence = uint16(rand.Intn(1 << 16))
}

func getICMPSequence() uint16 {
icmpSequenceMutex.Lock()
defer icmpSequenceMutex.Unlock()
Expand Down Expand Up @@ -129,7 +147,7 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
}

body := &icmp.Echo{
ID: os.Getpid() & 0xffff,
ID: icmpID,
Seq: int(getICMPSequence()),
Data: data,
}
Expand Down