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Merge pull request #20193 from MathiasVP/fix-fp-in-overflow-buffer

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C++: Fix FP in `cpp/overflow-buffer`
This commit is contained in:
Mathias Vorreiter Pedersen
2025-08-11 10:45:06 +02:00
committed by GitHub
parent a1bc865691 b00107f927
commit 851cb04d36
4 changed files with 45 additions and 19 deletions
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22
cpp/ql/lib/semmle/code/cpp/commons/Buffer.qll
View File

@@ -57,6 +57,18 @@ 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`.
*/
@@ -64,12 +76,8 @@ 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
@@ -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)
)
)

4
cpp/ql/src/change-notes/2025-08-08-overflow-buffer.md Normal file
View File

@@ -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
cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/UnboundedWrite.expected
View File

@@ -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 | |
@@ -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
@@ -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 |

14
cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/tests.cpp
View File

@@ -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];