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Merge pull request #18615 from MathiasVP/fix-fp-buffer-overflow
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C++: Fix FPs in `cpp/overflow-buffer`
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@MathiasVP
MathiasVP authored Jan 29, 2025
2 parents 6e31214 + 48cae7e commit 4b2c7ef
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Showing 6 changed files with 80 additions and 16 deletions.
21 changes: 18 additions & 3 deletions cpp/ql/lib/semmle/code/cpp/commons/Buffer.qll
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Expand Up @@ -54,13 +54,28 @@ private int isSource(Expr bufferExpr, Element why) {
result = bufferExpr.(AllocationExpr).getSizeBytes() and
why = bufferExpr
or
exists(Type bufferType |
exists(Type bufferType, Variable v |
v = why and
// buffer is the address of a variable
why = bufferExpr.(AddressOfExpr).getAddressable() and
bufferType = why.(Variable).getUnspecifiedType() and
result = bufferType.getSize() and
bufferType = v.getUnspecifiedType() and
not bufferType instanceof ReferenceType and
not any(Union u).getAMemberVariable() = why
|
not v instanceof Field and
result = bufferType.getSize()
or
// If it's an address of a field (i.e., a non-static member variable)
// then it's okay to use that address to access the other member variables.
// For example, this is okay:
// ```
// struct S { uint8_t a, b, c; };
// S s;
// memset(&s.a, 0, sizeof(S) - offsetof(S, a));
exists(Field f |
v = f and
result = f.getDeclaringType().getSize() - f.getByteOffset()
)
)
or
exists(Union bufferType |
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4 changes: 4 additions & 0 deletions cpp/ql/src/change-notes/2025-01-28-overflow-buffer.md
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@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* The "Call to memory access function may overflow buffer" query (`cpp/overflow-buffer`) now produces fewer FPs involving non-static member variables.
2 changes: 1 addition & 1 deletion cpp/ql/test/query-tests/Security/CWE/CWE-119/SAMATE/UnboundedWrite.expected
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@@ -1,4 +1,4 @@
edges
subpaths
nodes
subpaths
#select
4 changes: 4 additions & 0 deletions cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowBuffer.expected
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Expand Up @@ -49,6 +49,10 @@
| tests.cpp:577:7:577:13 | access to array | This array indexing operation accesses a negative index -1 on the $@. | tests.cpp:565:7:565:12 | buffer | array |
| tests.cpp:637:6:637:15 | access to array | This array indexing operation accesses a negative index -1 on the $@. | tests.cpp:633:7:633:12 | buffer | array |
| tests.cpp:645:7:645:13 | access to array | This array indexing operation accesses a negative index -1 on the $@. | tests.cpp:633:7:633:12 | buffer | array |
| tests.cpp:708:3:708:8 | call to memset | This 'memset' operation accesses 24 bytes but the $@ is only 8 bytes. | tests.cpp:693:16:693:16 | c | destination buffer |
| tests.cpp:712:3:712:8 | call to memset | This 'memset' operation accesses 16 bytes but the $@ is only 8 bytes. | tests.cpp:693:16:693:16 | c | destination buffer |
| tests.cpp:716:3:716:8 | call to memset | This 'memset' operation accesses 24 bytes but the $@ is only 16 bytes. | tests.cpp:692:16:692:16 | b | destination buffer |
| tests.cpp:727:2:727:7 | call to memset | This 'memset' operation accesses 24 bytes but the $@ is only 8 bytes. | tests.cpp:693:16:693:16 | c | destination buffer |
| tests_restrict.c:12:2:12:7 | call to memcpy | This 'memcpy' operation accesses 2 bytes but the $@ is only 1 byte. | tests_restrict.c:7:6:7:13 | smallbuf | source buffer |
| unions.cpp:26:2:26:7 | call to memset | This 'memset' operation accesses 200 bytes but the $@ is only 100 bytes. | unions.cpp:21:10:21:11 | mu | destination buffer |
| unions.cpp:30:2:30:7 | call to memset | This 'memset' operation accesses 200 bytes but the $@ is only 100 bytes. | unions.cpp:15:7:15:11 | small | destination buffer |
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24 changes: 12 additions & 12 deletions cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/UnboundedWrite.expected
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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:689:32:689:35 | **argv | provenance | |
| main.cpp:10:20:10:23 | *argv | tests.cpp:689:32:689:35 | *argv | provenance | |
| main.cpp:10:20:10:23 | **argv | tests.cpp:730:32:730:35 | **argv | provenance | |
| main.cpp:10:20:10:23 | *argv | tests.cpp:730:32:730:35 | *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:628:14:628:14 | *s [*home] | tests.cpp:628:14:628:19 | *home | provenance | |
| tests.cpp:628:14:628:14 | *s [*home] | tests.cpp:628:16:628:19 | *home | provenance | |
| tests.cpp:628:16:628:19 | *home | tests.cpp:628:14:628:19 | *home | provenance | |
| tests.cpp:689:32:689:35 | **argv | tests.cpp:714:9:714:15 | *access to array | provenance | |
| tests.cpp:689:32:689:35 | **argv | tests.cpp:715:9:715:15 | *access to array | provenance | |
| tests.cpp:689:32:689:35 | *argv | tests.cpp:714:9:714:15 | *access to array | provenance | |
| tests.cpp:689:32:689:35 | *argv | tests.cpp:715:9:715:15 | *access to array | provenance | |
| tests.cpp:714:9:714:15 | *access to array | tests.cpp:613:19:613:24 | *source | provenance | |
| tests.cpp:715:9:715:15 | *access to array | tests.cpp:622:19:622:24 | *source | provenance | |
| tests.cpp:730:32:730:35 | **argv | tests.cpp:755:9:755:15 | *access to array | provenance | |
| tests.cpp:730:32:730:35 | **argv | tests.cpp:756:9:756:15 | *access to array | provenance | |
| tests.cpp:730:32:730:35 | *argv | tests.cpp:755:9:755:15 | *access to array | provenance | |
| tests.cpp:730:32:730:35 | *argv | tests.cpp:756:9:756:15 | *access to array | provenance | |
| tests.cpp:755:9:755:15 | *access to array | tests.cpp:613:19:613:24 | *source | provenance | |
| tests.cpp:756:9:756:15 | *access to array | tests.cpp:622:19:622:24 | *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:628:14:628:14 | *s [*home] | semmle.label | *s [*home] |
| tests.cpp:628:14:628:19 | *home | semmle.label | *home |
| tests.cpp:628:16:628:19 | *home | semmle.label | *home |
| tests.cpp:689:32:689:35 | **argv | semmle.label | **argv |
| tests.cpp:689:32:689:35 | *argv | semmle.label | *argv |
| tests.cpp:714:9:714:15 | *access to array | semmle.label | *access to array |
| tests.cpp:715:9:715:15 | *access to array | semmle.label | *access to array |
| tests.cpp:730:32:730:35 | **argv | semmle.label | **argv |
| tests.cpp:730:32:730:35 | *argv | semmle.label | *argv |
| tests.cpp:755:9:755:15 | *access to array | semmle.label | *access to array |
| tests.cpp:756:9:756:15 | *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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41 changes: 41 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 @@ -685,6 +685,47 @@ int test28(MYSTRUCTREF g)
return memcmp(&g, &_myStruct, sizeof(MYSTRUCT)); // GOOD
}

#define offsetof(s, m) __builtin_offsetof(s, m)

struct HasSomeFields {
unsigned long a;
unsigned long b;
unsigned long c;

void test29() {
memset(&a, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, a)); // GOOD
};

void test30() {
memset(&b, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, b)); // GOOD
};

void test31() {
memset(&c, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, c)); // GOOD
};

void test32() {
memset(&c, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, a)); // BAD
};

void test33() {
memset(&c, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, b)); // BAD
};

void test34() {
memset(&b, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, a)); // BAD
};

void test35() {
memset(&b, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, b) - sizeof(unsigned long)); // GOOD
};
};

void test36() {
HasSomeFields hsf;
memset(&hsf.a, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, a)); // GOOD
memset(&hsf.c, 0, sizeof(HasSomeFields) - offsetof(HasSomeFields, a)); // BAD
}

int tests_main(int argc, char *argv[])
{
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