[dfsan] Add wrappers for v*printf functions

[gbalats]

Summary

Functions vsnprintf, vsprintf and vfprintf commonly occur in DFSan warnings.

[stephan.yichao.zhao]

compiler-rt/test/dfsan/custom.cpp

1948

We added test cases here to verify these functions' behavior.
Although internally we know it does the same as others, it would still be good to apply some tests. Can reusing sprintf's test code reduce duplicated test code?

[stephan.yichao.zhao]

vfprintf is actually a potential output point, and can be considered as a sink.

It is like __dfsw_write, and needs a callback so that users can decide whether to take this as a sink.

[gbalats]

compiler-rt/test/dfsan/custom.cpp

1948

This is what I started with but it ended up either over-complicating the test or adding duplicated code. Do you expect it's ever possible for the implementations of sprintf and vsprintf to diverge?

[stephan.yichao.zhao]

compiler-rt/test/dfsan/custom.cpp

1948

int sprintf_ish( char * s, const char * format, ... )
{
  va_list args;
  va_start (args, format);
  int r = vsprintf (s ,format, args);
  va_end (args);
  return r;
}

// When testing vsprintf
#define PRINT sprintf_ish
// When testing sprintf
#define PRINT sprintf

sprintf_ish is like a conversion from ... to va_list.
The existing sprintf test code needs a function like this kind of signature. I am not sure if in C we can define a function pointer with ... argument.
If not, we can replace those sprintf in the current test code by PRINT, and define PRINT differently when testing sprintf and vsprintf.
If function pointer works, then we can carry on a pointer to sprintf_ish.

[stephan.yichao.zhao]

compiler-rt/test/dfsan/custom.cpp

1948

re "Do you expect ... to diverge?": I guess no, while testing them mainly protects dfsan_custom.cpp in case anyone changes them in the future.

[gbalats]

compiler-rt/test/dfsan/custom.cpp

1948

Tried to share the testing code by introducing a function pointer and then passing either s(n)printf or vs(n)printf respectively. However, this seems to hit a DFSan limitation by being unable to handle indirect calls to variable-argument functions:

==57096==FATAL: DataFlowSanitizer: unsupported indirect call to vararg function snprintf

The macro idea would require all the testing code for these functions to be turned into a macro as well so that we can instantiate it twice, which would be very clunky.

[stephan.yichao.zhao]

Please remove vfprintf from the change's description or add a TODO in vfprintf about adding a callback to track it as an output point.

[gbalats]

In D106195#2884750, @stephan.yichao.zhao wrote:

vfprintf is actually a potential output point, and can be considered as a sink.

It is like __dfsw_write, and needs a callback so that users can decide whether to take this as a sink.

Isn't this the same for fprintf then which is also discarded currently?

[stephan.yichao.zhao]

In D106195#2898145, @gbalats wrote:

In D106195#2884750, @stephan.yichao.zhao wrote:

vfprintf is actually a potential output point, and can be considered as a sink.

It is like __dfsw_write, and needs a callback so that users can decide whether to take this as a sink.

Isn't this the same for fprintf then which is also discarded currently?

If we wanted to track output accurately, maybe fprintf also needs a callback. But this is out of the scope of this change.

compiler-rt/lib/dfsan/dfsan_custom.cpp

int __dfso_snprintf(char *str, size_t size, const char *format,
   va_list ap;
   va_start(ap, ret_origin);
   int ret = format_buffer(str, size, format, va_labels, ret_label, va_origins,
                           ret_origin, ap);
   va_end(ap);
   return ret;
 }
 
+SANITIZER_INTERFACE_ATTRIBUTE
+int __dfsw_vsprintf(char *str, const char *format, dfsan_label str_label,
+                    dfsan_label format_label, dfsan_label *va_labels,
+                    dfsan_label *ret_label, va_list ap) {
+  int ret = format_buffer(str, ~0ul, format, va_labels, ret_label, nullptr,
+                          nullptr, ap);
+  return ret;
+}
+
+SANITIZER_INTERFACE_ATTRIBUTE
+int __dfso_vsprintf(char *str, const char *format, dfsan_label str_label,
+                    dfsan_label format_label, dfsan_label *va_labels,
+                    dfsan_label *ret_label, dfsan_origin str_origin,
+                    dfsan_origin format_origin, dfsan_origin *va_origins,
+                    dfsan_origin *ret_origin, va_list ap) {
+  int ret = format_buffer(str, ~0ul, format, va_labels, ret_label, va_origins,
+                          ret_origin, ap);
+  return ret;
+}
+
+SANITIZER_INTERFACE_ATTRIBUTE
+int __dfsw_vsnprintf(char *str, size_t size, const char *format,
+                     dfsan_label str_label, dfsan_label size_label,
+                     dfsan_label format_label, dfsan_label *va_labels,
+                     dfsan_label *ret_label, va_list ap) {
+  int ret = format_buffer(str, size, format, va_labels, ret_label, nullptr,
+                          nullptr, ap);
+  return ret;
+}
+
+SANITIZER_INTERFACE_ATTRIBUTE
+int __dfso_vsnprintf(char *str, size_t size, const char *format,
+                     dfsan_label str_label, dfsan_label size_label,
+                     dfsan_label format_label, dfsan_label *va_labels,
+                     dfsan_label *ret_label, dfsan_origin str_origin,
+                     dfsan_origin size_origin, dfsan_origin format_origin,
+                     dfsan_origin *va_origins, dfsan_origin *ret_origin,
+                     va_list ap) {
+  int ret = format_buffer(str, size, format, va_labels, ret_label, va_origins,
+                          ret_origin, ap);
+  return ret;
+}
+
 static void BeforeFork() {
   StackDepotLockAll();
   GetChainedOriginDepot()->LockAll();
 }
 
 static void AfterFork() {
   GetChainedOriginDepot()->UnlockAll();
   StackDepotUnlockAll();

compiler-rt/lib/dfsan/done_abilist.txt

 fun:socket=discard
 fun:strerror=discard
 fun:strspn=discard
 fun:strcspn=discard
 fun:symlink=discard
 fun:syscall=discard
 fun:unlink=discard
 fun:uselocale=discard
+fun:vfprintf=discard
 
 # Functions that produce output does not depend on the input (need to zero the
 # shadow manually).
 fun:_dl_get_tls_static_info=custom
 fun:clock_gettime=custom
 fun:dlopen=custom
 fun:epoll_wait=custom
 fun:fgets=custom

 fun:sigemptyset=custom
 fun:sigaction=custom
 fun:signal=custom
 fun:gettimeofday=custom
 
 # sprintf-like
 fun:sprintf=custom
 fun:snprintf=custom
+fun:vsprintf=custom
+fun:vsnprintf=custom
 
 # TODO: custom
 fun:asprintf=discard
 fun:qsort=discard
 
 # fork
 fun:fork=custom
 

compiler-rt/test/dfsan/custom.cpp

#endif
   ASSERT_INIT_ORIGINS(buf + 7, 2, s_o);
   ASSERT_READ_LABEL(buf + 9, 4, 0);
   ASSERT_READ_LABEL(buf + 13, 4, i_label);
   ASSERT_INIT_ORIGINS(buf + 13, 4, y_o);
   ASSERT_READ_LABEL(buf + 17, 2, 0);
   ASSERT_LABEL(r, 0);
 }
 
+// This is essentially the same as sprintf with the only difference that it
+// uses a va_list instead of varargs. This empty function is here to appease
+// the check-wrappers script.
+void test_vsprintf() {}
+
+// Same here, but for snprintf.
+void test_vsnprintf() {}
+
 // Tested by a seperate source file.  This empty function is here to appease the
 // check-wrappers script.
 void test_fork() {}
 
 int main(void) {
   i_label = 1;
   j_label = 2;
   k_label = 4;
int main(void) {
   test_strrchr();
   test_strstr();
   test_strtod();
   test_strtol();
   test_strtoll();
   test_strtoul();
   test_strtoull();
   test_time();
+  test_vsprintf();
+  test_vsnprintf();
   test_write();
 }