bootstat: better validation of battery level (shutdown,battery)

Replace simple strtoull with loop that ensures no leading zeros.
Restrict size of value buffer being checked as allocation was
going to end of retrieved buffer, which can cause unnecessary
memory pressure during boot.

Test: system/core/bootstat/boot_reason_test.sh
Bug: 63736262
Change-Id: Ifdc1d4fd3a73794c001577024ce7cbfde9c25028

1 files changed, 18 insertions, 6 deletions

diff --git a/bootstat/bootstat.cpp b/bootstat/bootstat.cpp
index 07d410c91..cdb4b9b3b 100644
--- a/bootstat/bootstat.cpp
+++ b/bootstat/bootstat.cpp
@@ -508,10 +508,16 @@ std::string BootReasonStrToReason(const std::string& boot_reason) {
       size_t pos = content.rfind(battery);  // last one
       std::string digits;
       if (pos != std::string::npos) {
-        digits = content.substr(pos + strlen(battery));
+        digits = content.substr(pos + strlen(battery), strlen("100 "));
+      }
+      const char* endptr = digits.c_str();
+      unsigned level = 0;
+      while (::isdigit(*endptr)) {
+        level *= 10;
+        level += *endptr++ - '0';
+        // make sure no leading zeros, except zero itself, and range check.
+        if ((level == 0) || (level > 100)) break;
       }
-      char* endptr = NULL;
-      unsigned long long level = strtoull(digits.c_str(), &endptr, 10);
       if ((level <= 100) && (endptr != digits.c_str()) && (*endptr == ' ')) {
         LOG(INFO) << "Battery level at shutdown " << level << "%";
         if (level <= battery_dead_threshold) {
@@ -552,10 +558,16 @@ std::string BootReasonStrToReason(const std::string& boot_reason) {
 
         pos = content.find(match);  // The first one it finds.
         if (pos != std::string::npos) {
-          digits = content.substr(pos + strlen(match));
+          digits = content.substr(pos + strlen(match), strlen("100 "));
+        }
+        endptr = digits.c_str();
+        level = 0;
+        while (::isdigit(*endptr)) {
+          level *= 10;
+          level += *endptr++ - '0';
+          // make sure no leading zeros, except zero itself, and range check.
+          if ((level == 0) || (level > 100)) break;
         }
-        endptr = NULL;
-        level = strtoull(digits.c_str(), &endptr, 10);
         if ((level <= 100) && (endptr != digits.c_str()) && (*endptr == ' ')) {
           LOG(INFO) << "Battery level at startup " << level << "%";
           if (level <= battery_dead_threshold) {