mirror of
https://github.com/safing/portmaster
synced 2025-09-01 18:19:12 +00:00
54 lines
1.5 KiB
Go
54 lines
1.5 KiB
Go
package network
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import (
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"github.com/safing/portbase/log"
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"github.com/safing/portbase/rng"
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)
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// GetUnusedLocalPort returns a local port of the specified protocol that is
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// currently unused and is unlikely to be used within the next seconds.
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func GetUnusedLocalPort(protocol uint8) (port uint16, ok bool) {
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allConns := conns.clone()
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tries := 1000
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hundredth := tries / 100
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// Try up to 1000 times to find an unused port.
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nextPort:
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for i := 0; i < tries; i++ {
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// Generate random port between 10000 and 65535
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rN, err := rng.Number(55535)
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if err != nil {
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log.Warningf("network: failed to generate random port: %s", err)
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return 0, false
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}
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port := uint16(rN + 10000)
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// Shrink range when we chew through the tries.
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portRangeStart := port - uint16(100-(i/hundredth))
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// Check if the generated port is unused.
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nextConnection:
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for _, conn := range allConns {
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// Skip connection if the protocol does not match the protocol of interest.
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if conn.Entity.Protocol != protocol {
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continue nextConnection
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}
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// Skip port if the local port is in dangerous proximity.
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// Consecutive port numbers are very common.
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if conn.LocalPort <= port && conn.LocalPort >= portRangeStart {
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continue nextPort
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}
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}
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// Log if it took more than 10 attempts.
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if i >= 10 {
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log.Warningf("network: took %d attempts to find a suitable unused port for pre-auth", i+1)
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}
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// The checks have passed. We have found a good unused port.
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return port, true
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}
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return 0, false
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}
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