Fix some ubsan failures in erasure tests KIKIMR-18923

2 files changed, 13 insertions, 9 deletions

diff --git a/ydb/core/erasure/erasure_perf_test.cpp b/ydb/core/erasure/erasure_perf_test.cpp
index 79965e9bdeb..5983da63560 100644
--- a/ydb/core/erasure/erasure_perf_test.cpp
+++ b/ydb/core/erasure/erasure_perf_test.cpp
@@ -101,7 +101,10 @@ std::pair<double, double> MeasureTime(TErasureType &type, TVector<ui32> &missedP
             for (ui32 i = 0; i < type.TotalPartCount(); ++i) {
                 auto data = partSet.Parts[i].OwnedString.GetContiguousSpan();
                 TString newOwnedString(partSize, '\0');
-                memcpy(newOwnedString.Detach(), data.data(), data.size());
+                if (data.size() > 0) {
+                    Y_VERIFY(partSize >= data.size());
+                    memcpy(newOwnedString.Detach(), data.data(), data.size());
+                }
                 partSet.Parts[i].ReferenceTo(partSet.Parts[i].OwnedString);
             }
         }
diff --git a/ydb/core/erasure/ut_util.h b/ydb/core/erasure/ut_util.h
index ef2f7236553..4f994158a11 100644
--- a/ydb/core/erasure/ut_util.h
+++ b/ydb/core/erasure/ut_util.h
@@ -5,6 +5,7 @@
 #include <util/random/mersenne64.h>
 #include <util/stream/null.h>
 #include <util/string/printf.h>
+#include <util/system/unaligned_mem.h>
 
 IOutputStream& Ctest = Cnull;
 
@@ -56,15 +57,15 @@ inline void GenNextCombination(ui32 *variants, ui32 const k, ui32 const n) {
 inline TString GenerateRandomString(NPrivate::TMersenne64 &randGen, size_t dataSize) {
     TString testString;
     testString.resize(dataSize);
-    char *writePosChar = (char *)testString.data();
-    ui32 charParts = testString.size() % sizeof(ui64);
-    for (ui32 i = 0; i < charParts; ++i) {
-        writePosChar[i] = (char)randGen.GenRand();
+    char *p = testString.Detach();
+    while (dataSize >= sizeof(ui64)) {
+        WriteUnaligned<ui64>(p, randGen.GenRand());
+        p += sizeof(ui64);
+        dataSize -= sizeof(ui64);
     }
-    ui64 *writePos64 = (ui64 *)writePosChar;
-    ui32 ui64Parts = testString.size() / sizeof(ui64);
-    for (ui32 i = 0; i < ui64Parts; ++i) {
-        writePos64[i] = randGen.GenRand();
+    while (dataSize > 0) {
+        *p++ = (char)randGen.GenRand();
+        --dataSize;
     }
     return testString;
 }