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CPP: Fix some use after free FPs. #14275

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Merged
MathiasVP merged 4 commits into from
Oct 3, 2023
Merged

CPP: Fix some use after free FPs. #14275

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9de6230
CPP: Add use after free false positive example.
alexet Sep 20, 2023
d084931
CPP: Fix use after free FPs by elimnatiing freeing nodes rather than …
alexet Sep 20, 2023
2860c0c
CPP: Move test into correct file.
alexet Sep 27, 2023
6b0ae0f
CPP: Remove unned argument from use-after-free
alexet Sep 27, 2023
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11 changes: 5 additions & 6 deletions cpp/ql/src/Critical/UseAfterFree.ql
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Original file line number Diff line number Diff line change
Expand Up @@ -29,8 +29,7 @@ private predicate externalCallNeverDereferences(FormattingFunctionCall call, int
)
}

predicate isUse0(DataFlow::Node n, Expr e) {
e = n.asExpr() and
predicate isUse0(Expr e) {
not isFree(_, e, _) and
(
e = any(PointerDereferenceExpr pde).getOperand()
Expand All @@ -43,7 +42,7 @@ predicate isUse0(DataFlow::Node n, Expr e) {
or
// Assume any function without a body will dereference the pointer
exists(int i, Call call, Function f |
n.asExpr() = call.getArgument(i) and
e = call.getArgument(i) and
f = call.getTarget() and
not f.hasEntryPoint() and
// Exclude known functions we know won't dereference the pointer.
Expand All @@ -57,7 +56,7 @@ module ParameterSinks {
import semmle.code.cpp.ir.ValueNumbering

predicate flowsToUse(DataFlow::Node n) {
isUse0(n, _)
isUse0(n.asExpr())
or
exists(DataFlow::Node succ |
flowsToUse(succ) and
Expand Down Expand Up @@ -90,7 +89,7 @@ module ParameterSinks {
) {
pragma[only_bind_out](source.asParameter()) = pragma[only_bind_out](init.getParameter()) and
paramToUse(source, sink) and
isUse0(sink, _)
isUse0(sink.asExpr())
}

private InitializeParameterInstruction getAnAlwaysDereferencedParameter0() {
Expand Down Expand Up @@ -139,7 +138,7 @@ module IsUse {
private import semmle.code.cpp.ir.dataflow.internal.DataFlowImplCommon

predicate isUse(DataFlow::Node n, Expr e) {
isUse0(n, e)
isUse0(e) and n.asExpr() = e
or
exists(CallInstruction call, InitializeParameterInstruction init |
n.asOperand().getDef().getUnconvertedResultExpression() = e and
Expand Down
1 change: 1 addition & 0 deletions cpp/ql/test/query-tests/Critical/MemoryFreed/MemoryFreed.expected
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Expand Up @@ -96,6 +96,7 @@
| test_free.cpp:255:10:255:10 | p |
| test_free.cpp:260:9:260:9 | p |
| test_free.cpp:263:12:263:12 | p |
| test_free.cpp:269:7:269:11 | ... = ... |
| virtual.cpp:18:10:18:10 | a |
| virtual.cpp:19:10:19:10 | c |
| virtual.cpp:38:10:38:10 | b |
Expand Down
1 change: 1 addition & 0 deletions cpp/ql/test/query-tests/Critical/MemoryFreed/MemoryMayNotBeFreed.expected
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@@ -1 +1,2 @@
| test_free.cpp:36:22:36:35 | ... = ... | This memory allocation may not be released at $@. | test_free.cpp:38:1:38:1 | return ... | this exit point |
| test_free.cpp:267:12:267:17 | call to malloc | This memory allocation may not be released at $@. | test_free.cpp:270:1:270:1 | return ... | this exit point |
6 changes: 6 additions & 0 deletions cpp/ql/test/query-tests/Critical/MemoryFreed/test_free.cpp
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Expand Up @@ -261,4 +261,10 @@ void test_ref_delete(int *&p) {
p = new int;
use(p); // GOOD
delete p; // GOOD
}

void test_free_assign() {
void *a = malloc(10);
void *b;
free(b = a); // GOOD
}