Prevent readTrainInfo from crashing statsd.

copy_n in readTrainInfo needs an input iterator and an output iterator.
When we read the size of the trainName, we were passing an
outputIterator that was a pointer to size_t. The goal was to fill up the
size_t with the length of the train. However, we need to do this byte by
byte, and by passing the pointer to the size_t, we increment by size_t
bytes instead of one bytes when we increment the iterator.

The change now is to use linux read, which is the mirror to how we write
the file. This code is cleaner and less error prone than reading the
file to a string.

Another thing this cl does is implement some sanity checks to make sure
we dont read pass the string input buffer, and to try to safeguard
against devices that upgrade from beta 1 to beta 2 and have a trainInfo
from beta1 stored on the device (since they are not backwards
compatible.) Another option here is to create a separate file for
everything besides the experiment ids, but that might not be deasible in
the time we have.

Test: storage manager unit tests pass
Test: debug phonesky apk to trigger binary push, manually inspecting the
file created to ensure the write works, and using adb shell cmd stats
pull-source to verify the read works.
Test: statsd testdrive 10051

Bug: 128460940
Change-Id: I3c08d946db9c43d77e5efca2eb1088adbb4a3ce1

cmds/statsd/src/storage/StorageManager.cpp

@@ -116,14 +116,16 @@ bool StorageManager::writeTrainInfo(int64_t trainVersionCode, const std::string&
     const size_t trainNameSizeByteCount = sizeof(trainNameSize);
     result = write(fd, (uint8_t*)&trainNameSize, trainNameSizeByteCount);
     if (result != trainNameSizeByteCount) {
-        VLOG("Failed to write %s", file_name.c_str());
+        VLOG("Failed to write train name size for %s", file_name.c_str());
+        close(fd);
         return false;
     }
 
     // Write trainName to file
     result = write(fd, trainName.c_str(), trainNameSize);
     if (result != trainNameSize) {
-        VLOG("Failed to write %s", file_name.c_str());
+        VLOG("Failed to write train name for%s", file_name.c_str());
+        close(fd);
         return false;
     }
 
@@ -131,7 +133,18 @@ bool StorageManager::writeTrainInfo(int64_t trainVersionCode, const std::string&
     const size_t statusByteCount = sizeof(status);
     result = write(fd, (uint8_t*)&status, statusByteCount);
     if (result != statusByteCount) {
-        VLOG("Failed to write %s", file_name.c_str());
+        VLOG("Failed to write status for %s", file_name.c_str());
+        close(fd);
+        return false;
+    }
+
+    // Write experiment id size to file.
+    const size_t experimentIdSize = experimentIds.size();
+    const size_t experimentIdsSizeByteCount = sizeof(experimentIdSize);
+    result = write(fd, (uint8_t*) &experimentIdSize, experimentIdsSizeByteCount);
+    if (result != experimentIdsSizeByteCount) {
+        VLOG("Failed to write experiment id size for %s", file_name.c_str());
+        close(fd);
         return false;
     }
 
@@ -140,13 +153,15 @@ bool StorageManager::writeTrainInfo(int64_t trainVersionCode, const std::string&
     if (result == experimentIds.size()) {
         VLOG("Successfully wrote %s", file_name.c_str());
     } else {
-        VLOG("Failed to write %s", file_name.c_str());
+        VLOG("Failed to write experiment ids for %s", file_name.c_str());
+        close(fd);
         return false;
     }
 
     result = fchown(fd, AID_STATSD, AID_STATSD);
     if (result) {
         VLOG("Failed to chown %s to statsd", file_name.c_str());
+        close(fd);
         return false;
     }
 
@@ -170,39 +185,73 @@ bool StorageManager::readTrainInfo(InstallTrainInfo& trainInfo) {
         if (name[0] == '.') {
             continue;
         }
+
+        size_t result;
+
         trainInfo.trainVersionCode = StrToInt64(name);
         string fullPath = StringPrintf("%s/%s", TRAIN_INFO_DIR, name);
         int fd = open(fullPath.c_str(), O_RDONLY | O_CLOEXEC);
-        if (fd != -1) {
-            string str;
-            if (android::base::ReadFdToString(fd, &str)) {
-                close(fd);
-
-                auto it = str.begin();
-
-                // Read # of bytes taken by trainName in the file
-                size_t trainNameSize;
-                const size_t trainNameSizeByteCount = sizeof(trainNameSize);
-                std::copy_n(it, trainNameSizeByteCount, &trainNameSize);
-                it += trainNameSizeByteCount;
-
-                // Read trainName
-                std::copy_n(it, trainNameSize, std::back_inserter(trainInfo.trainName));
-                it += trainNameSize;
-
-                // Read status
-                const size_t statusByteCount = sizeof(trainInfo.status);
-                std::copy_n(it, statusByteCount, &trainInfo.status);
-                it += statusByteCount;
-
-                // Read experimentIds
-                std::copy(it, str.end(), std::back_inserter(trainInfo.experimentIds));
-
-                VLOG("Read train info file successful: %s", fullPath.c_str());
-                return true;
-            }
+        if (fd == -1) {
+            return false;
         }
+
+        // Read # of bytes taken by trainName in the file.
+        size_t trainNameSize;
+        result = read(fd, &trainNameSize, sizeof(size_t));
+        if (result != sizeof(size_t)) {
+            VLOG("Failed to read train name size from file %s", fullPath.c_str());
+            close(fd);
+            return false;
+        }
+
+        // Read trainName
+        trainInfo.trainName.resize(trainNameSize);
+        result = read(fd, trainInfo.trainName.data(), trainNameSize);
+        if (result != trainNameSize) {
+            VLOG("Failed to read train name from file %s", fullPath.c_str());
+            close(fd);
+            return false;
+        }
+
+        // Read status
+        const size_t statusByteCount = sizeof(trainInfo.status);
+        result = read(fd, &trainInfo.status, statusByteCount);
+        if (result != statusByteCount) {
+            VLOG("Failed to read train status from file %s", fullPath.c_str());
+            close(fd);
+            return false;
+        }
+
+        // Read experiment ids size.
+        size_t experimentIdSize;
+        result = read(fd, &experimentIdSize, sizeof(size_t));
+        if (result != sizeof(size_t)) {
+            VLOG("Failed to read train experiment id size from file %s", fullPath.c_str());
+            close(fd);
+            return false;
+        }
+
+        // Read experimentIds
+        trainInfo.experimentIds.resize(experimentIdSize);
+        result = read(fd, trainInfo.experimentIds.data(), experimentIdSize);
+        if (result != experimentIdSize) {
+            VLOG("Failed to read train experiment ids from file %s", fullPath.c_str());
+            close(fd);
+            return false;
+        }
+
+        // Expect to be at EOF.
+        char c;
+        result = read(fd, &c, 1);
+        if (result != 0) {
+            VLOG("Failed to read train info from file %s. Did not get expected EOF.", fullPath.c_str());
+            close(fd);
+            return false;
+        }
+
+        VLOG("Read train info file successful: %s", fullPath.c_str());
         close(fd);
+        return true;
     }
     return false;
 }