[clang] [analyzer] TaintPropagation checker strlen() should not propagate (PR #66086)
Daniel Krupp via cfe-commits
cfe-commits at lists.llvm.org
Mon Sep 18 09:31:30 PDT 2023
https://github.com/dkrupp updated https://github.com/llvm/llvm-project/pull/66086
>From 889c886c3eed31335531ec61ad2b48bef15414d8 Mon Sep 17 00:00:00 2001
From: Daniel Krupp <daniel.krupp at ericsson.com>
Date: Fri, 8 Sep 2023 16:57:49 +0200
Subject: [PATCH] [analyzer] TaintPropagation checker strlen() should not
propagate
strlen(..) call should not propagate taintedness,
because it brings in many false positive findings.
It is a common pattern to copy user provided input
to another buffer. In these cases we always
get warnings about tainted data used as the malloc parameter:
buf = malloc(strlen(tainted_txt) + 1); // false warning
This pattern can lead to a denial of service attack only, when
the attacker can directly specify the size of the allocated area
as an arbitrary large number (e.g. the value is converted
from a user provided string).
Later, we could reintroduce strlen() as a taint propagating function
with the consideration not to emit warnings when the tainted value
cannot be "arbitrarily large" (such as the size of an already allocated
memory block).
---
clang/docs/ReleaseNotes.rst | 7 +++++
clang/docs/analyzer/checkers.rst | 4 +--
.../Checkers/GenericTaintChecker.cpp | 7 ++---
.../test/Analysis/taint-diagnostic-visitor.c | 13 +++++-----
clang/test/Analysis/taint-generic.c | 26 +++++++++++++------
5 files changed, 38 insertions(+), 19 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 3cdad2f7b9f0e5a..414cd7f62e2d764 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -409,6 +409,13 @@ Static Analyzer
bitwise shift operators produce undefined behavior (because some operand is
negative or too large).
+- The ``alpha.security.taint.TaintPropagation`` checker no longer propagates
+ taint on ``strlen`` and ``strnlen`` calls, unless these are marked
+ explicitly propagators in the user-provided taint configuration file.
+ This removal empirically reduces the number of false positive reports.
+ Read the PR for the details.
+ (`#66086 <https://github.com/llvm/llvm-project/pull/66086>`_)
+
.. _release-notes-sanitizers:
Sanitizers
diff --git a/clang/docs/analyzer/checkers.rst b/clang/docs/analyzer/checkers.rst
index 54ea49e7426cc86..dbd6d7787823530 100644
--- a/clang/docs/analyzer/checkers.rst
+++ b/clang/docs/analyzer/checkers.rst
@@ -2599,8 +2599,8 @@ Default propagations rules:
``memcpy``, ``memmem``, ``memmove``, ``mbtowc``, ``pread``, ``qsort``,
``qsort_r``, ``rawmemchr``, ``read``, ``recv``, ``recvfrom``, ``rindex``,
``strcasestr``, ``strchr``, ``strchrnul``, ``strcasecmp``, ``strcmp``,
- ``strcspn``, ``strlen``, ``strncasecmp``, ``strncmp``, ``strndup``,
- ``strndupa``, ``strnlen``, ``strpbrk``, ``strrchr``, ``strsep``, ``strspn``,
+ ``strcspn``, ``strncasecmp``, ``strncmp``, ``strndup``,
+ ``strndupa``, ``strpbrk``, ``strrchr``, ``strsep``, ``strspn``,
``strstr``, ``strtol``, ``strtoll``, ``strtoul``, ``strtoull``, ``tolower``,
``toupper``, ``ttyname``, ``ttyname_r``, ``wctomb``, ``wcwidth``
diff --git a/clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp
index 5da0f34b3d0464f..dae8ff0c5c8f1b8 100644
--- a/clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp
@@ -695,9 +695,10 @@ void GenericTaintChecker::initTaintRules(CheckerContext &C) const {
{{{"strpbrk"}}, TR::Prop({{0}}, {{ReturnValueIndex}})},
{{{"strndup"}}, TR::Prop({{0}}, {{ReturnValueIndex}})},
{{{"strndupa"}}, TR::Prop({{0}}, {{ReturnValueIndex}})},
- {{{"strlen"}}, TR::Prop({{0}}, {{ReturnValueIndex}})},
- {{{"wcslen"}}, TR::Prop({{0}}, {{ReturnValueIndex}})},
- {{{"strnlen"}}, TR::Prop({{0}}, {{ReturnValueIndex}})},
+
+ // strlen, wcslen, strnlen and alike intentionally don't propagate taint.
+ // See the details here: https://github.com/llvm/llvm-project/pull/66086
+
{{{"strtol"}}, TR::Prop({{0}}, {{1, ReturnValueIndex}})},
{{{"strtoll"}}, TR::Prop({{0}}, {{1, ReturnValueIndex}})},
{{{"strtoul"}}, TR::Prop({{0}}, {{1, ReturnValueIndex}})},
diff --git a/clang/test/Analysis/taint-diagnostic-visitor.c b/clang/test/Analysis/taint-diagnostic-visitor.c
index f1b9ceebdd9a6b8..8a7510177f3e444 100644
--- a/clang/test/Analysis/taint-diagnostic-visitor.c
+++ b/clang/test/Analysis/taint-diagnostic-visitor.c
@@ -10,6 +10,7 @@ int scanf(const char *restrict format, ...);
int system(const char *command);
char* getenv( const char* env_var );
size_t strlen( const char* str );
+int atoi( const char* str );
void *malloc(size_t size );
void free( void *ptr );
char *fgets(char *str, int n, FILE *stream);
@@ -54,11 +55,11 @@ void taintDiagnosticVLA(void) {
// propagating through variables and expressions
char *taintDiagnosticPropagation(){
char *pathbuf;
- char *pathlist=getenv("PATH"); // expected-note {{Taint originated here}}
+ char *size=getenv("SIZE"); // expected-note {{Taint originated here}}
// expected-note at -1 {{Taint propagated to the return value}}
- if (pathlist){ // expected-note {{Assuming 'pathlist' is non-null}}
+ if (size){ // expected-note {{Assuming 'size' is non-null}}
// expected-note at -1 {{Taking true branch}}
- pathbuf=(char*) malloc(strlen(pathlist)+1); // expected-warning{{Untrusted data is used to specify the buffer size}}
+ pathbuf=(char*) malloc(atoi(size)); // expected-warning{{Untrusted data is used to specify the buffer size}}
// expected-note at -1{{Untrusted data is used to specify the buffer size}}
// expected-note at -2 {{Taint propagated to the return value}}
return pathbuf;
@@ -71,12 +72,12 @@ char *taintDiagnosticPropagation(){
char *taintDiagnosticPropagation2(){
char *pathbuf;
char *user_env2=getenv("USER_ENV_VAR2");//unrelated taint source
- char *pathlist=getenv("PATH"); // expected-note {{Taint originated here}}
+ char *size=getenv("SIZE"); // expected-note {{Taint originated here}}
// expected-note at -1 {{Taint propagated to the return value}}
char *user_env=getenv("USER_ENV_VAR");//unrelated taint source
- if (pathlist){ // expected-note {{Assuming 'pathlist' is non-null}}
+ if (size){ // expected-note {{Assuming 'size' is non-null}}
// expected-note at -1 {{Taking true branch}}
- pathbuf=(char*) malloc(strlen(pathlist)+1); // expected-warning{{Untrusted data is used to specify the buffer size}}
+ pathbuf=(char*) malloc(atoi(size)+1); // expected-warning{{Untrusted data is used to specify the buffer size}}
// expected-note at -1{{Untrusted data is used to specify the buffer size}}
// expected-note at -2 {{Taint propagated to the return value}}
return pathbuf;
diff --git a/clang/test/Analysis/taint-generic.c b/clang/test/Analysis/taint-generic.c
index c674a03cfaec6c8..10a52cb44259551 100644
--- a/clang/test/Analysis/taint-generic.c
+++ b/clang/test/Analysis/taint-generic.c
@@ -443,14 +443,18 @@ int testSprintf_propagates_taint(char *buf, char *msg) {
return 1 / x; // expected-warning {{Division by a tainted value, possibly zero}}
}
-void test_wchar_apis_propagate(const char *path) {
+void test_wchar_apis_dont_propagate(const char *path) {
+ // strlen, wcslen, strnlen and alike intentionally don't propagate taint.
+ // See the details here: https://github.com/llvm/llvm-project/pull/66086
+ // This isn't ideal, but this is only what we have now.
+
FILE *f = fopen(path, "r");
clang_analyzer_isTainted_charp((char*)f); // expected-warning {{YES}}
wchar_t wbuf[10];
fgetws(wbuf, sizeof(wbuf)/sizeof(*wbuf), f);
clang_analyzer_isTainted_wchar(*wbuf); // expected-warning {{YES}}
int n = wcslen(wbuf);
- clang_analyzer_isTainted_int(n); // expected-warning {{YES}}
+ clang_analyzer_isTainted_int(n); // expected-warning {{NO}}
wchar_t dst[100] = L"ABC";
clang_analyzer_isTainted_wchar(*dst); // expected-warning {{NO}}
@@ -458,7 +462,7 @@ void test_wchar_apis_propagate(const char *path) {
clang_analyzer_isTainted_wchar(*dst); // expected-warning {{YES}}
int m = wcslen(dst);
- clang_analyzer_isTainted_int(m); // expected-warning {{YES}}
+ clang_analyzer_isTainted_int(m); // expected-warning {{NO}}
}
int scanf_s(const char *format, ...);
@@ -948,21 +952,27 @@ void testStrndupa(size_t n) {
}
size_t strlen(const char *s);
-void testStrlen() {
+void testStrlen_dont_propagate() {
+ // strlen, wcslen, strnlen and alike intentionally don't propagate taint.
+ // See the details here: https://github.com/llvm/llvm-project/pull/66086
+ // This isn't ideal, but this is only what we have now.
char s[10];
scanf("%9s", s);
size_t result = strlen(s);
- clang_analyzer_isTainted_int(result); // expected-warning {{YES}}
+ // strlen propagating taint would bring in many false positives
+ clang_analyzer_isTainted_int(result); // expected-warning {{NO}}
}
size_t strnlen(const char *s, size_t maxlen);
-void testStrnlen(size_t maxlen) {
+void testStrnlen_dont_propagate(size_t maxlen) {
+ // strlen, wcslen, strnlen and alike intentionally don't propagate taint.
+ // See the details here: https://github.com/llvm/llvm-project/pull/66086
+ // This isn't ideal, but this is only what we have now.
char s[10];
scanf("%9s", s);
-
size_t result = strnlen(s, maxlen);
- clang_analyzer_isTainted_int(result); // expected-warning {{YES}}
+ clang_analyzer_isTainted_int(result); // expected-warning {{NO}}
}
long strtol(const char *restrict nptr, char **restrict endptr, int base);
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