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fix(dialer): enforce IP block list before socket creation #124

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fix(dialer): enforce IP block list before socket creation #124

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15 changes: 13 additions & 2 deletions internal/dialer/dialer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,8 @@ var ErrForbiddenRequest = errors.New("forbidden")
// Dialer is a wrapper around net.Dialer that uses a dnscache.Resolver to cache DNS lookups.
type Dialer struct {
net.Dialer
resolver *dnscache.Resolver
resolver *dnscache.Resolver
blockedIPs []net.IP
}

// New creates a new Dialer.
Expand All @@ -25,7 +26,8 @@ func New(resolver *dnscache.Resolver, blockedIps []net.IP) *Dialer {
Dialer: net.Dialer{
Control: safeControl(blockedIps),
},
resolver: resolver,
resolver: resolver,
blockedIPs: blockedIps,
}
}

Expand All @@ -47,6 +49,15 @@ func (d *Dialer) DialContext(ctx context.Context, network, address string) (conn
return nil, err
}
for _, ip := range ips {
// Check against the blocked list before attempting socket creation.
// safeControl fires after the socket is opened, which can fail first on
// systems that don't support a particular address family (e.g. IPv6).
parsed := net.ParseIP(ip)
for _, blocked := range d.blockedIPs {
if parsed != nil && parsed.Equal(blocked) {
return nil, ErrForbiddenRequest
}
}
conn, err = d.Dialer.DialContext(ctx, network, net.JoinHostPort(ip, port))
if err == nil {
break
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