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Brodes/overflow buffer fixes upstream #17384

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merged 11 commits into from
Sep 11, 2024
Merged

Brodes/overflow buffer fixes upstream #17384

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9105375
Addreessing false positive due to incorrect use of getType
bdrodes Aug 8, 2024
abd0a07
Addressing false positive with strncpy.
bdrodes Aug 8, 2024
f0eeaaf
BufferAccess must be reachable. False positives observed where access…
bdrodes Aug 12, 2024
e4d2990
Formatting and updating tests.
bdrodes Aug 12, 2024
cc953c8
Added test case to demonstrate type error corrected in this branch.
bdrodes Sep 4, 2024
77b88af
Removing commented out code and altering comments to explain why the …
bdrodes Sep 4, 2024
6f1aade
Added change log
bdrodes Sep 4, 2024
7889895
Updating change log
bdrodes Sep 4, 2024
8ab22fe
Update cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/test…
bdrodes Sep 5, 2024
1005a89
Updating test cases.
bdrodes Sep 5, 2024
58779e1
Merge branch 'main' into brodes/overflow-buffer-fixes-upstream
bdrodes Sep 10, 2024
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2 changes: 1 addition & 1 deletion 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 @@ -57,7 +57,7 @@ private int isSource(Expr bufferExpr, Element why) {
exists(Type bufferType |
// buffer is the address of a variable
why = bufferExpr.(AddressOfExpr).getAddressable() and
bufferType = why.(Variable).getType() and
bufferType = why.(Variable).getUnspecifiedType() and
result = bufferType.getSize() and
not bufferType instanceof ReferenceType and
not any(Union u).getAMemberVariable() = why
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10 changes: 8 additions & 2 deletions cpp/ql/lib/semmle/code/cpp/security/BufferAccess.qll
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Expand Up @@ -14,7 +14,11 @@ int getPointedSize(Type t) {
* BufferWrite differ.
*/
abstract class BufferAccess extends Expr {
BufferAccess() { not this.isUnevaluated() }
BufferAccess() {
not this.isUnevaluated() and
//A buffer access must be reachable (not in dead code)
reachable(this)
}

abstract string getName();

Expand All @@ -26,6 +30,8 @@ abstract class BufferAccess extends Expr {
* - 1 = buffer range [0, getSize) is accessed entirely.
* - 2 = buffer range [0, getSize) may be accessed partially or entirely.
* - 3 = buffer is accessed at offset getSize - 1.
* - 4 = buffer is accessed with null terminator read protections
* (does not read past null terminator, regardless of access size)
*/
abstract Expr getBuffer(string bufferDesc, int accessType);

Expand Down Expand Up @@ -128,7 +134,7 @@ class StrncpyBA extends BufferAccess {
or
result = this.(FunctionCall).getArgument(1) and
bufferDesc = "source buffer" and
accessType = 2
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accessType = 4
}

override Expr getSizeExpr() { result = this.(FunctionCall).getArgument(2) }
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4 changes: 3 additions & 1 deletion cpp/ql/src/Critical/OverflowStatic.ql
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Expand Up @@ -42,7 +42,9 @@ class BufferAccess extends ArrayExpr {
not exists(Macro m |
m.getName() = "strcmp" and
m.getAnInvocation().getAnExpandedElement() = this
)
) and
//A buffer access must be reachable (not in dead code)
reachable(this)
}

int bufferSize() { staticBuffer(this.getArrayBase(), _, result) }
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1 change: 1 addition & 0 deletions cpp/ql/src/Security/CWE/CWE-119/OverflowBuffer.ql
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ from
BufferAccess ba, string bufferDesc, int accessSize, int accessType, Element bufferAlloc,
int bufferSize, string message
where
accessType != 4 and
accessSize = ba.getSize() and
bufferSize = getBufferSize(ba.getBuffer(bufferDesc, accessType), bufferAlloc) and
(
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5 changes: 5 additions & 0 deletions cpp/ql/src/change-notes/2024-09-04-overflow-buffer-false-positives.md
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@@ -0,0 +1,5 @@
---
category: minorAnalysis
---
* Removed false positives caused by buffer accesses in unreachable code
* Removed false positives caused by inconsistent type checking
26 changes: 13 additions & 13 deletions cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/UnboundedWrite.expected
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Expand Up @@ -31,9 +31,9 @@ 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:657:32:657:35 | **argv | provenance | |
| main.cpp:10:20:10:23 | *argv | tests.cpp:657:32:657:35 | **argv | provenance | |
| main.cpp:10:20:10:23 | *argv | tests.cpp:657:32:657:35 | *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:689:32:689:35 | **argv | provenance | |
| main.cpp:10:20:10:23 | *argv | tests.cpp:689:32:689:35 | *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 @@ -46,12 +46,12 @@ 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:657:32:657:35 | **argv | tests.cpp:682:9:682:15 | *access to array | provenance | |
| tests.cpp:657:32:657:35 | **argv | tests.cpp:683:9:683:15 | *access to array | provenance | |
| tests.cpp:657:32:657:35 | *argv | tests.cpp:682:9:682:15 | *access to array | provenance | |
| tests.cpp:657:32:657:35 | *argv | tests.cpp:683:9:683:15 | *access to array | provenance | |
| tests.cpp:682:9:682:15 | *access to array | tests.cpp:613:19:613:24 | *source | provenance | |
| tests.cpp:683:9:683:15 | *access to array | tests.cpp:622:19:622:24 | *source | 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_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 @@ -85,10 +85,10 @@ 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:657:32:657:35 | **argv | semmle.label | **argv |
| tests.cpp:657:32:657:35 | *argv | semmle.label | *argv |
| tests.cpp:682:9:682:15 | *access to array | semmle.label | *access to array |
| tests.cpp:683:9:683:15 | *access to array | semmle.label | *access to array |
| 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_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 |
Expand Down
32 changes: 32 additions & 0 deletions cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/tests.cpp
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Expand Up @@ -654,6 +654,38 @@ void test26(bool cond)
if (ptr[-1] == 0) { return; } // GOOD: accesses buffer[1]
}

#define IND 100
#define MAX_SIZE 100
void test27(){
char *src = "";
char *dest = "abcdefgh";
int ind = 100;
char buffer[MAX_SIZE];

strncpy(dest, src, 8); // GOOD, strncpy will not read past null terminator of source

if(IND < MAX_SIZE){
buffer[IND] = 0; // GOOD: out of bounds, but inaccessible code
}
}

typedef struct _MYSTRUCT {
unsigned long a;
unsigned short b;
unsigned char z[ 100 ];
} MYSTRUCT;


const MYSTRUCT _myStruct = { 0 };
typedef const MYSTRUCT& MYSTRUCTREF;

// False positive case due to use of typedefs
int test28(MYSTRUCTREF g)
{
return memcmp(&g, &_myStruct, sizeof(MYSTRUCT)); // GOOD
}


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