[clang-tools-extra] 6e7dd1e - [clangd] Assert on varint encoding

[Kadir Cetinkaya via cfe-commits]

Author: Kadir Cetinkaya
Date: 2020-11-13T17:01:07+01:00
New Revision: 6e7dd1e3e1170080b76b5dcc5716bdd974343233

URL: https://github.com/llvm/llvm-project/commit/6e7dd1e3e1170080b76b5dcc5716bdd974343233
DIFF: https://github.com/llvm/llvm-project/commit/6e7dd1e3e1170080b76b5dcc5716bdd974343233.diff

LOG: [clangd] Assert on varint encoding

5th byte of a varint can't be bigger than 0x0f, fix a test and add an
assertion.

Differential Revision: https://reviews.llvm.org/D91405

Added: 
    

Modified: 
    clang-tools-extra/clangd/index/Serialization.cpp
    clang-tools-extra/clangd/unittests/SerializationTests.cpp

Removed: 
    


################################################################################
diff  --git a/clang-tools-extra/clangd/index/Serialization.cpp b/clang-tools-extra/clangd/index/Serialization.cpp
index 0b82224fa715..8b0ae3925a2f 100644
--- a/clang-tools-extra/clangd/index/Serialization.cpp
+++ b/clang-tools-extra/clangd/index/Serialization.cpp
@@ -21,6 +21,7 @@
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/raw_ostream.h"
+#include <cstdint>
 #include <vector>
 
 namespace clang {
@@ -81,12 +82,17 @@ class Reader {
 
   uint32_t consumeVar() {
     constexpr static uint8_t More = 1 << 7;
-    uint8_t B = consume8();
+
+    // Use a 32 bit unsigned here to prevent promotion to signed int (unless int
+    // is wider than 32 bits).
+    uint32_t B = consume8();
     if (LLVM_LIKELY(!(B & More)))
       return B;
     uint32_t Val = B & ~More;
     for (int Shift = 7; B & More && Shift < 32; Shift += 7) {
       B = consume8();
+      // 5th byte of a varint can only have lowest 4 bits set.
+      assert((Shift != 28 || B == (B & 0x0f)) && "Invalid varint encoding");
       Val |= (B & ~More) << Shift;
     }
     return Val;

diff  --git a/clang-tools-extra/clangd/unittests/SerializationTests.cpp b/clang-tools-extra/clangd/unittests/SerializationTests.cpp
index 94db6c9127a8..ca7d3ba7e3e1 100644
--- a/clang-tools-extra/clangd/unittests/SerializationTests.cpp
+++ b/clang-tools-extra/clangd/unittests/SerializationTests.cpp
@@ -366,9 +366,9 @@ TEST(SerializationTest, NoCrashOnBadArraySize) {
   Pos += FileDigest.size();
 
   // Varints are little-endian base-128 numbers, where the top-bit of each byte
-  // indicates whether there are more. 8fffffff7f -> 0xffffffff.
+  // indicates whether there are more. ffffffff0f -> 0xffffffff.
   std::string CorruptSrcs =
-      (Srcs->Data.take_front(Pos) + llvm::fromHex("8fffffff7f") +
+      (Srcs->Data.take_front(Pos) + llvm::fromHex("ffffffff0f") +
        "some_random_garbage")
           .str();
   Srcs->Data = CorruptSrcs;