logd: Fix ClearUidLogs() when writer_active_ is true

Previously ClearUidLogs() would Compress() the log buffer in all
cases, however that is the wrong behavior when writer_active_ is true
and would leave the SerializedLogChunk object in an invalid state.  If
more logs are written to the log, then write_offset() will be higher
than the compressed size of the log, violating a CHECK() when later
decompressing the log.

This change does not call Compress() in ClearUidLogs() if
writer_active_ is true.  It upgrades a check in Compress() from a
simple if statement to a CHECK() to prevent against this happening in
the future.

It adds a test that exercises the previously failing path.

Bug: 166187079
Test: unit tests
Change-Id: Ic5fbcf16f724af1c20170b8f4e6e2daadf6a9529

1 files changed, 24 insertions, 0 deletions

diff --git a/logd/SerializedLogChunkTest.cpp b/logd/SerializedLogChunkTest.cpp
index f10b9c673..3b451252d 100644
--- a/logd/SerializedLogChunkTest.cpp
+++ b/logd/SerializedLogChunkTest.cpp
@@ -281,3 +281,27 @@ TEST_P(UidClearTest, save_beginning_and_end) {
 }
 
 INSTANTIATE_TEST_CASE_P(UidClearTests, UidClearTest, testing::Values(true, false));
+
+// b/166187079: ClearUidLogs() should not compress the log if writer_active_ is true
+TEST(SerializedLogChunk, ClearUidLogs_then_FinishWriting) {
+    static constexpr size_t kChunkSize = 10 * 4096;
+    static constexpr uid_t kUidToClear = 1000;
+    static constexpr uid_t kOtherUid = 1234;
+
+    SerializedLogChunk chunk{kChunkSize};
+    static const char msg1[] = "saved first message";
+    static const char msg2[] = "cleared interior message";
+    static const char msg3[] = "last message stays";
+    ASSERT_NE(nullptr, chunk.Log(1, log_time(), kOtherUid, 1, 2, msg1, sizeof(msg1)));
+    ASSERT_NE(nullptr, chunk.Log(2, log_time(), kUidToClear, 1, 2, msg2, sizeof(msg2)));
+    ASSERT_NE(nullptr, chunk.Log(3, log_time(), kOtherUid, 1, 2, msg3, sizeof(msg3)));
+
+    chunk.ClearUidLogs(kUidToClear, LOG_ID_MAIN, nullptr);
+
+    ASSERT_NE(nullptr, chunk.Log(4, log_time(), kOtherUid, 1, 2, msg3, sizeof(msg3)));
+
+    chunk.FinishWriting();
+    // The next line would violate a CHECK() during decompression with the faulty code.
+    chunk.IncReaderRefCount();
+    chunk.DecReaderRefCount();
+}