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Prevent a nil pointer dereference segfault #120

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merged 2 commits into from
May 3, 2024
Merged

Prevent a nil pointer dereference segfault #120

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023c8e1
Prevent a nil pointer dereference segfault
boydjeff Apr 19, 2024
7c6a612
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boydjeff May 3, 2024
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23 changes: 20 additions & 3 deletions client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -151,24 +151,24 @@ func newClient(v4 bool, v6 bool) (*client, error) {
var mconn6 *net.UDPConn
var err error

// Establish unicast connections
if v4 {
uconn4, err = net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
if err != nil {
log.Printf("[ERR] mdns: Failed to bind to udp4 port: %v", err)
}
}

if v6 {
uconn6, err = net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
if err != nil {
log.Printf("[ERR] mdns: Failed to bind to udp6 port: %v", err)
}
}

if uconn4 == nil && uconn6 == nil {
return nil, fmt.Errorf("failed to bind to any unicast udp port")
}

// Establish multicast connections
if v4 {
mconn4, err = net.ListenMulticastUDP("udp4", nil, ipv4Addr)
if err != nil {
Expand All @@ -181,11 +181,28 @@ func newClient(v4 bool, v6 bool) (*client, error) {
log.Printf("[ERR] mdns: Failed to bind to udp6 port: %v", err)
}
}

if mconn4 == nil && mconn6 == nil {
return nil, fmt.Errorf("failed to bind to any multicast udp port")
}

// Check that unicast and multicast connections have been made for IPv4 and IPv6
// and disable the respective protocol if not.
if uconn4 == nil || mconn4 == nil {
logger.Printf("[INFO] mdns: Failed to listen to both unicast and multicast on IPv4")
uconn4 = nil
mconn4 = nil
v4 = false
}
if uconn6 == nil || mconn6 == nil {
logger.Printf("[INFO] mdns: Failed to listen to both unicast and multicast on IPv6")
uconn6 = nil
mconn6 = nil
v6 = false
}
if !v4 && !v6 {
return nil, fmt.Errorf("at least one of IPv4 and IPv6 must be enabled for querying")
}

c := &client{
use_ipv4: v4,
use_ipv6: v6,
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