- Issue #2588, #2589: Fix potential integer underflow and overflow
conditions in the PyOS_vsnprintf C API function.
This is a backport of r63728 and r63734 from trunk.
diff --git a/Misc/NEWS b/Misc/NEWS
index 4eb8a80..6363f80 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -41,6 +41,9 @@
less than zero will now raise a SystemError and return NULL to indicate a
bug in the calling C code.
+- Issue #2588, #2589: Fix potential integer underflow and overflow
+ conditions in the PyOS_vsnprintf C API function.
+
Library
-------
diff --git a/Python/mysnprintf.c b/Python/mysnprintf.c
index 4d3770d..3173863 100644
--- a/Python/mysnprintf.c
+++ b/Python/mysnprintf.c
@@ -54,18 +54,28 @@
PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
{
int len; /* # bytes written, excluding \0 */
-#ifndef HAVE_SNPRINTF
+#ifdef HAVE_SNPRINTF
+#define _PyOS_vsnprintf_EXTRA_SPACE 1
+#else
+#define _PyOS_vsnprintf_EXTRA_SPACE 512
char *buffer;
#endif
assert(str != NULL);
assert(size > 0);
assert(format != NULL);
+ /* We take a size_t as input but return an int. Sanity check
+ * our input so that it won't cause an overflow in the
+ * vsnprintf return value or the buffer malloc size. */
+ if (size > INT_MAX - _PyOS_vsnprintf_EXTRA_SPACE) {
+ len = -666;
+ goto Done;
+ }
#ifdef HAVE_SNPRINTF
len = vsnprintf(str, size, format, va);
#else
/* Emulate it. */
- buffer = PyMem_MALLOC(size + 512);
+ buffer = PyMem_MALLOC(size + _PyOS_vsnprintf_EXTRA_SPACE);
if (buffer == NULL) {
len = -666;
goto Done;
@@ -75,7 +85,7 @@
if (len < 0)
/* ignore the error */;
- else if ((size_t)len >= size + 512)
+ else if ((size_t)len >= size + _PyOS_vsnprintf_EXTRA_SPACE)
Py_FatalError("Buffer overflow in PyOS_snprintf/PyOS_vsnprintf");
else {
@@ -86,8 +96,10 @@
str[to_copy] = '\0';
}
PyMem_FREE(buffer);
-Done:
#endif
- str[size-1] = '\0';
+Done:
+ if (size > 0)
+ str[size-1] = '\0';
return len;
+#undef _PyOS_vsnprintf_EXTRA_SPACE
}