auth.c: implement polkit support for FreeBSD

FreeBSD's analog to SO_PEERCRED is LOCAL_PEERCRED, which returns a
(ABI stable) `struct xucred` rather than a `struct cred`.  Paper over the
platform differences with a typedef and a couple macros.

src/auth.c

@@ -53,17 +53,32 @@
 
 #ifdef HAVE_POLKIT
 
-#if defined(SO_PEERCRED)
+#if defined(SO_PEERCRED) || defined(LOCAL_PEERCRED)
 
 #include <polkit/polkit.h>
 #include <stdbool.h>
 
+#ifdef __FreeBSD__
+
+#include <sys/ucred.h>
+typedef struct xucred platform_cred;
+#define CRED_PID(uc) (uc).cr_pid
+#define CRED_UID(uc) (uc).cr_uid
+
+#else
+
+typedef struct ucred platform_cred;
+#define CRED_PID(uc) (uc).pid
+#define CRED_UID(uc) (uc).uid
+
+#endif
+
 extern bool disable_polkit;
 
 /* Returns non zero when the client is authorized */
 unsigned IsClientAuthorized(int socket, const char* action, const char* reader)
 {
- struct ucred cr;
+ platform_cred cr;
  socklen_t cr_len;
  int ret;
  PolkitSubject *subject;
@@ -79,7 +94,11 @@ unsigned IsClientAuthorized(int socket, const char* action, const char* reader)
  snprintf(action_name, sizeof(action_name), "org.debian.pcsc-lite.%s", action);
 
  cr_len = sizeof(cr);
+#ifdef LOCAL_PEERCRED
+ ret = getsockopt(socket, SOL_LOCAL, LOCAL_PEERCRED, &cr, &cr_len);
+#else
  ret = getsockopt(socket, SOL_SOCKET, SO_PEERCRED, &cr, &cr_len);
+#endif
  if (ret == -1)
  {
 #ifndef NO_LOG
@@ -99,7 +118,7 @@ unsigned IsClientAuthorized(int socket, const char* action, const char* reader)
  return 0;
  }
 
- subject = polkit_unix_process_new_for_owner(cr.pid, 0, cr.uid);
+ subject = polkit_unix_process_new_for_owner(CRED_PID(cr), 0, CRED_UID(cr));
  if (subject == NULL)
  {
  Log1(PCSC_LOG_CRITICAL, "polkit_unix_process_new_for_owner failed");
@@ -146,7 +165,7 @@ unsigned IsClientAuthorized(int socket, const char* action, const char* reader)
  {
  Log4(PCSC_LOG_CRITICAL,
  "Process %u (user: %u) is NOT authorized for action: %s",
- (unsigned)cr.pid, (unsigned)cr.uid, action);
+ (unsigned)CRED_PID(cr), (unsigned)CRED_UID(cr), action);
  }
 
  if (result)