logd: validate and fill in socket credentials

- android::pidToUid() additional checking.  Make sure if we have to
  convert a PID to an UID that the parse of /proc/<pid>/status
  requires a trailing space after the number
- android::tidToPid() added, in the same vein as android::pidToUid().
- stats.tidToPid() added
- If no credentials, set PID to 0 and UID to DEFAULT_OVERFLOWUID
- If credentialed PID is 0, use stats.tidToPid()
- If credentialed UID is DEFAULT_OVERFLOWUID, use stats.pidToUid()

Test: remove +passcred from logd.rc for daemon and confirm very few
      UID=65534 or PID=0 cases actually show up
Bug: 37985222
Change-Id: I7d20506e70e67beb3043d1537cf9450ab58dc278
diff --git a/logd/LogStatistics.cpp b/logd/LogStatistics.cpp
index d20d90e..af59ddc 100644
--- a/logd/LogStatistics.cpp
+++ b/logd/LogStatistics.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <ctype.h>
 #include <fcntl.h>
 #include <inttypes.h>
 #include <pwd.h>
@@ -824,8 +825,10 @@
     FILE* fp = fopen(buffer, "r");
     if (fp) {
         while (fgets(buffer, sizeof(buffer), fp)) {
-            int uid;
-            if (sscanf(buffer, "Uid: %d", &uid) == 1) {
+            int uid = AID_LOGD;
+            char space = 0;
+            if ((sscanf(buffer, "Uid: %d%c", &uid, &space) == 2) &&
+                isspace(space)) {
                 fclose(fp);
                 return uid;
             }
@@ -834,12 +837,35 @@
     }
     return AID_LOGD;  // associate this with the logger
 }
+
+pid_t tidToPid(pid_t tid) {
+    char buffer[512];
+    snprintf(buffer, sizeof(buffer), "/proc/%u/status", tid);
+    FILE* fp = fopen(buffer, "r");
+    if (fp) {
+        while (fgets(buffer, sizeof(buffer), fp)) {
+            int pid = tid;
+            char space = 0;
+            if ((sscanf(buffer, "Tgid: %d%c", &pid, &space) == 2) &&
+                isspace(space)) {
+                fclose(fp);
+                return pid;
+            }
+        }
+        fclose(fp);
+    }
+    return tid;
+}
 }
 
 uid_t LogStatistics::pidToUid(pid_t pid) {
     return pidTable.add(pid)->second.getUid();
 }
 
+pid_t LogStatistics::tidToPid(pid_t tid) {
+    return tidTable.add(tid)->second.getPid();
+}
+
 // caller must free character string
 const char* LogStatistics::pidToName(pid_t pid) const {
     // An inconvenient truth ... getName() can alter the object