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Avoid undefined behavior when nullptr is passed to memcpy with size 0

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This commit is contained in:
Roman Gershman 2019-05-23 06:03:35 +03:00 committed by Derek Mauro
parent ce65f5ac3c
commit 27c30ec671
2 changed files with 25 additions and 5 deletions
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16
absl/strings/str_cat.cc
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@ -89,7 +89,9 @@ static char* Append(char* out, const AlphaNum& x) {
// memcpy is allowed to overwrite arbitrary memory, so doing this after the
// call would force an extra fetch of x.size().
char* after = out + x.size();
memcpy(out, x.data(), x.size());
if (x.size() != 0) {
memcpy(out, x.data(), x.size());
}
return after;
}
@ -146,8 +148,10 @@ std::string CatPieces(std::initializer_list<absl::string_view> pieces) {
char* out = begin;
for (const absl::string_view piece : pieces) {
const size_t this_size = piece.size();
memcpy(out, piece.data(), this_size);
out += this_size;
if (this_size != 0) {
memcpy(out, piece.data(), this_size);
out += this_size;
}
}
assert(out == begin + result.size());
return result;
@ -176,8 +180,10 @@ void AppendPieces(std::string* dest,
char* out = begin + old_size;
for (const absl::string_view piece : pieces) {
const size_t this_size = piece.size();
memcpy(out, piece.data(), this_size);
out += this_size;
if (this_size != 0) {
memcpy(out, piece.data(), this_size);
out += this_size;
}
}
assert(out == begin + dest->size());
}

14
absl/strings/str_cat_test.cc
View file

@ -408,6 +408,20 @@ TEST(StrCat, VectorBoolReferenceTypes) {
EXPECT_EQ(result, "1010");
}
// Passing nullptr to memcpy is undefined behavior and this test
// provides coverage of codepaths that handle empty strings with nullptrs.
TEST(StrCat, AvoidsMemcpyWithNullptr) {
EXPECT_EQ(absl::StrCat(42, absl::string_view{}), "42");
// Cover CatPieces code.
EXPECT_EQ(absl::StrCat(1, 2, 3, 4, 5, absl::string_view{}), "12345");
// Cover AppendPieces.
std::string result;
absl::StrAppend(&result, 1, 2, 3, 4, 5, absl::string_view{});
EXPECT_EQ(result, "12345");
}
#ifdef GTEST_HAS_DEATH_TEST
TEST(StrAppend, Death) {
std::string s = "self";