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C++: Fix FP in cpp/overflow-buffer #20193

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Merged
merged 4 commits into from
Aug 11, 2025
+45 −19
Merged

C++: Fix FP in cpp/overflow-buffer #20193

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26be983
C++: Add FP.
MathiasVP Aug 8, 2025
d76ce4f
C++: Also handle reference types when computing 'trueSize'.
MathiasVP Aug 8, 2025
0c9d14f
C++: Accept test changes.
MathiasVP Aug 8, 2025
b00107f
C++: Add change note.
MathiasVP Aug 8, 2025
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22 changes: 15 additions & 7 deletions cpp/ql/lib/semmle/code/cpp/commons/Buffer.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -57,19 +57,27 @@ private Class getRootType(FieldAccess fa) {
)
}

/**
* Gets the size of `v`. This predicate does not have a result when the
* unspecified type of `v` is a `ReferenceType`.
*/
private int getVariableSize(Variable v) {
exists(Type t |
t = v.getUnspecifiedType() and
not t instanceof ReferenceType and
result = t.getSize()
)
}

/**
* Gets the size of the buffer access at `va`.
*/
private int getSize(VariableAccess va) {
exists(Variable v | va.getTarget() = v |
// If `v` is not a field then the size of the buffer is just
// the size of the type of `v`.
exists(Type t |
t = v.getUnspecifiedType() and
not v instanceof Field and
not t instanceof ReferenceType and
result = t.getSize()
)
not v instanceof Field and
result = getVariableSize(v)
or
exists(Class c, int trueSize |
// Otherwise, we find the "outermost" object and compute the size
Expand All @@ -92,7 +100,7 @@ private int getSize(VariableAccess va) {
// buffer is `12 - 4 = 8`.
c = getRootType(va) and
// we calculate the size based on the last field, to avoid including any padding after it
trueSize = max(Field f | | f.getOffsetInClass(c) + f.getUnspecifiedType().getSize()) and
trueSize = max(Field f | | f.getOffsetInClass(c) + getVariableSize(f)) and
result = trueSize - v.(Field).getOffsetInClass(c)
)
)
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4 changes: 4 additions & 0 deletions cpp/ql/src/change-notes/2025-08-08-overflow-buffer.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* Fixed a false positive in `cpp/overflow-buffer` when the type of the destination buffer is a reference to a class/struct type.
24 changes: 12 additions & 12 deletions cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/UnboundedWrite.expected
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Original file line number Diff line number Diff line change
Expand Up @@ -27,8 +27,8 @@ edges
| main.cpp:9:29:9:32 | *argv | tests_restrict.c:15:41:15:44 | *argv | provenance | |
| main.cpp:9:29:9:32 | tests_restrict_main output argument | main.cpp:10:20:10:23 | **argv | provenance | |
| main.cpp:9:29:9:32 | tests_restrict_main output argument | main.cpp:10:20:10:23 | *argv | provenance | |
| main.cpp:10:20:10:23 | **argv | tests.cpp:1060:32:1060:35 | **argv | provenance | |
| main.cpp:10:20:10:23 | *argv | tests.cpp:1060:32:1060:35 | *argv | provenance | |
| main.cpp:10:20:10:23 | **argv | tests.cpp:1074:32:1074:35 | **argv | provenance | |
| main.cpp:10:20:10:23 | *argv | tests.cpp:1074:32:1074:35 | *argv | provenance | |
| overflowdestination.cpp:23:45:23:48 | **argv | overflowdestination.cpp:23:45:23:48 | **argv | provenance | |
| overflowdestination.cpp:23:45:23:48 | **argv | overflowdestination.cpp:23:45:23:48 | *argv | provenance | |
| test_buffer_overrun.cpp:32:46:32:49 | **argv | test_buffer_overrun.cpp:32:46:32:49 | **argv | provenance | |
Expand All @@ -41,12 +41,12 @@ edges
| tests.cpp:649:14:649:14 | *s [*home] | tests.cpp:649:14:649:19 | *home | provenance | |
| tests.cpp:649:14:649:14 | *s [*home] | tests.cpp:649:16:649:19 | *home | provenance | |
| tests.cpp:649:16:649:19 | *home | tests.cpp:649:14:649:19 | *home | provenance | |
| tests.cpp:1060:32:1060:35 | **argv | tests.cpp:1085:9:1085:15 | *access to array | provenance | |
| tests.cpp:1060:32:1060:35 | **argv | tests.cpp:1086:9:1086:15 | *access to array | provenance | |
| tests.cpp:1060:32:1060:35 | *argv | tests.cpp:1085:9:1085:15 | *access to array | provenance | |
| tests.cpp:1060:32:1060:35 | *argv | tests.cpp:1086:9:1086:15 | *access to array | provenance | |
| tests.cpp:1085:9:1085:15 | *access to array | tests.cpp:634:19:634:24 | *source | provenance | |
| tests.cpp:1086:9:1086:15 | *access to array | tests.cpp:643:19:643:24 | *source | provenance | |
| tests.cpp:1074:32:1074:35 | **argv | tests.cpp:1099:9:1099:15 | *access to array | provenance | |
| tests.cpp:1074:32:1074:35 | **argv | tests.cpp:1100:9:1100:15 | *access to array | provenance | |
| tests.cpp:1074:32:1074:35 | *argv | tests.cpp:1099:9:1099:15 | *access to array | provenance | |
| tests.cpp:1074:32:1074:35 | *argv | tests.cpp:1100:9:1100:15 | *access to array | provenance | |
| tests.cpp:1099:9:1099:15 | *access to array | tests.cpp:634:19:634:24 | *source | provenance | |
| tests.cpp:1100:9:1100:15 | *access to array | tests.cpp:643:19:643:24 | *source | provenance | |
| tests_restrict.c:15:41:15:44 | **argv | tests_restrict.c:15:41:15:44 | **argv | provenance | |
| tests_restrict.c:15:41:15:44 | *argv | tests_restrict.c:15:41:15:44 | *argv | provenance | |
nodes
Expand Down Expand Up @@ -80,10 +80,10 @@ nodes
| tests.cpp:649:14:649:14 | *s [*home] | semmle.label | *s [*home] |
| tests.cpp:649:14:649:19 | *home | semmle.label | *home |
| tests.cpp:649:16:649:19 | *home | semmle.label | *home |
| tests.cpp:1060:32:1060:35 | **argv | semmle.label | **argv |
| tests.cpp:1060:32:1060:35 | *argv | semmle.label | *argv |
| tests.cpp:1085:9:1085:15 | *access to array | semmle.label | *access to array |
| tests.cpp:1086:9:1086:15 | *access to array | semmle.label | *access to array |
| tests.cpp:1074:32:1074:35 | **argv | semmle.label | **argv |
| tests.cpp:1074:32:1074:35 | *argv | semmle.label | *argv |
| tests.cpp:1099:9:1099:15 | *access to array | semmle.label | *access to array |
| tests.cpp:1100:9:1100:15 | *access to array | semmle.label | *access to array |
| tests_restrict.c:15:41:15:44 | **argv | semmle.label | **argv |
| tests_restrict.c:15:41:15:44 | **argv | semmle.label | **argv |
| tests_restrict.c:15:41:15:44 | *argv | semmle.label | *argv |
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14 changes: 14 additions & 0 deletions cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1057,6 +1057,20 @@ void test30() {
strncpy(us.buffer2, "", sizeof(us) - 1); // BAD
}

struct S_Size16 {
unsigned short uint16;
unsigned char uint8;
unsigned char raw[13];
};

void test31() {
S_Size16 e;

[&e](void* data){
memcpy(&e, data, sizeof(e)); // GOOD
};
}

int tests_main(int argc, char *argv[])
{
long long arr17[19];
Expand Down