[lldb/Utility] Fix DecodeUUIDBytesFromString not to access past the input buffer

[friss]

Summary

The current logig in this function reads:

while (!p.empty()) {
   if (isxdigit(p[0]) && isxdigit(p[1])) {

if p is of size one when entering the loop, the second isxdigit
will access past the end of the buffer. This patch takes the simplest
approach of verifying that the buffer is at least of size 2.

[friss]

I would have committed this right away if it weren't for the slight change in behavior I wanted to point out. With this patch, if an input string ends with a -, it won't be consumed anymore. I suppose it doesn't matter.

[labath]

In D80807#2063196, @friss wrote:

I would have committed this right away if it weren't for the slight change in behavior I wanted to point out. With this patch, if an input string ends with a -, it won't be consumed anymore. I suppose it doesn't matter.

That looks fine. A trailing - looks like someone wanted to add more bytes but then pressed return too early, so rejecting that sounds perfectly reasonable.

Since you've obviously been looking at this code lately, I've also added you the to D80755, for the mac perspective of accepting "uuid"s with different lengths.

[friss]

Abandon in favor of D80755

lldb/source/Utility/UUID.cpp

 //===-- UUID.cpp ----------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
static inline int xdigit_to_int(char ch) {
   return ch - '0';
 }
 
 llvm::StringRef
 UUID::DecodeUUIDBytesFromString(llvm::StringRef p,
                                 llvm::SmallVectorImpl<uint8_t> &uuid_bytes,
                                 uint32_t num_uuid_bytes) {
   uuid_bytes.clear();
-  while (!p.empty()) {
+  while (p.size() > 1) {
     if (isxdigit(p[0]) && isxdigit(p[1])) {
       int hi_nibble = xdigit_to_int(p[0]);
       int lo_nibble = xdigit_to_int(p[1]);
       // Translate the two hex nibble characters into a byte
       uuid_bytes.push_back((hi_nibble << 4) + lo_nibble);
 
       // Skip both hex digits
       p = p.drop_front(2);

lldb/unittests/Utility/UUIDTest.cpp

 //===-- UUIDTest.cpp ------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
TEST(UUIDTest, SetFromStringRef) {
   EXPECT_EQ(UUID::fromData("@ABCDEFGHIJKLMNO", 16), u);
 
   EXPECT_EQ(45u, u.SetFromStringRef(
                      "40-41-42-43-4445464748494a4b4c4d4e4f-50515253", 20));
   EXPECT_EQ(UUID::fromData("@ABCDEFGHIJKLMNOPQRS", 20), u);
 
   EXPECT_EQ(0u, u.SetFromStringRef("40-41-42-43-4445464748494a4b4c4d4e4f", 20));
   EXPECT_EQ(0u, u.SetFromStringRef("40xxxxx"));
+  EXPECT_EQ(0u, u.SetFromStringRef("404142434445464748494a4b4c4d4e4"));
   EXPECT_EQ(0u, u.SetFromStringRef(""));
   EXPECT_EQ(UUID::fromData("@ABCDEFGHIJKLMNOPQRS", 20), u)
       << "uuid was changed by failed parse calls";
 
   EXPECT_EQ(
       32u, u.SetFromStringRef("404142434445464748494a4b4c4d4e4f-50515253", 16));
   EXPECT_EQ(UUID::fromData("@ABCDEFGHIJKLMNO", 16), u);
 }