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[Wunsafe-buffer-usage] Fix false positives in handling string literals. #115552

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Merged
merged 1 commit into from
Nov 12, 2024
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[Wunsafe-buffer-usage] Fix false positives in handling string literals. #115552

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28 changes: 19 additions & 9 deletions clang/lib/Analysis/UnsafeBufferUsage.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -436,21 +436,31 @@ AST_MATCHER(ArraySubscriptExpr, isSafeArraySubscript) {

const auto *BaseDRE =
dyn_cast<DeclRefExpr>(Node.getBase()->IgnoreParenImpCasts());
if (!BaseDRE)
return false;
if (!BaseDRE->getDecl())
return false;
const auto *CATy = Finder->getASTContext().getAsConstantArrayType(
BaseDRE->getDecl()->getType());
if (!CATy)
const auto *SLiteral =
dyn_cast<StringLiteral>(Node.getBase()->IgnoreParenImpCasts());
uint64_t size;

if (!BaseDRE && !SLiteral)
return false;

if (BaseDRE) {
if (!BaseDRE->getDecl())
return false;
const auto *CATy = Finder->getASTContext().getAsConstantArrayType(
BaseDRE->getDecl()->getType());
if (!CATy) {
return false;
}
size = CATy->getLimitedSize();
} else if (SLiteral) {
size = SLiteral->getLength() + 1;
}

if (const auto *IdxLit = dyn_cast<IntegerLiteral>(Node.getIdx())) {
const APInt ArrIdx = IdxLit->getValue();
// FIXME: ArrIdx.isNegative() we could immediately emit an error as that's a
// bug
if (ArrIdx.isNonNegative() &&
ArrIdx.getLimitedValue() < CATy->getLimitedSize())
if (ArrIdx.isNonNegative() && ArrIdx.getLimitedValue() < size)
return true;
}

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14 changes: 14 additions & 0 deletions clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -38,3 +38,17 @@ void constant_idx_unsafe(unsigned idx) {
// expected-note@-1{{change type of 'buffer' to 'std::array' to label it for hardening}}
buffer[10] = 0; // expected-note{{used in buffer access here}}
}

void constant_id_string(unsigned idx) {
char safe_char = "abc"[1]; // no-warning
safe_char = ""[0];
safe_char = "\0"[0];

char abcd[5] = "abc";
abcd[2]; // no-warning

char unsafe_char = "abc"[3];
unsafe_char = "abc"[-1]; //expected-warning{{unsafe buffer access}}
unsafe_char = ""[1]; //expected-warning{{unsafe buffer access}}
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This shouldn't be a warning either.

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@malavikasamak malavikasamak Nov 11, 2024 •
edited
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In this case, I think we should warn, as the length here including the null terminator is 1.

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Sorry, my bad. You're right

unsafe_char = ""[idx]; //expected-warning{{unsafe buffer access}}
}
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