1 files changed, 54 insertions, 0 deletions
diff --git a/src/lib/malloc-overflow.h b/src/lib/malloc-overflow.h
new file mode 100644
index 0000000..108cc00
--- /dev/null
+++ b/src/lib/malloc-overflow.h
@@ -0,0 +1,54 @@
+#ifndef MALLOC_OVERFLOW_H
+#define MALLOC_OVERFLOW_H
+
+/* MALLOC_*() can be used to calculate memory allocation sizes. If there's an
+   overflow, it'll cleanly panic instead of causing a potential buffer
+   overflow.
+
+   Note that *_malloc(size+1) doesn't need to use MALLOC_ADD(size, 1). It wraps
+   to size==0 and the *_malloc() calls already panic if size==0. */
+static inline size_t
+malloc_multiply_check(size_t a, size_t b, size_t sizeof_a, size_t sizeof_b,
+		      const char *fname, unsigned int linenum)
+{
+	/* the first sizeof-checks are intended to optimize away this entire
+	   if-check for types that are small enough to never wrap size_t. */
+	if ((sizeof_a * 2 > sizeof(size_t) || sizeof_b * 2 > sizeof(size_t)) &&
+	    b != 0 && (a > SIZE_MAX / b)) {
+		i_panic("file %s: line %d: memory allocation overflow: %zu * %zu",
+			fname, linenum, a, b);
+	}
+	return a * b;
+}
+#ifndef STATIC_CHECKER
+#  define MALLOC_MULTIPLY(a, b) \
+	malloc_multiply_check(a, b, sizeof(a), sizeof(b), __FILE__, __LINE__)
+#else
+/* avoid warning every time about sizeof(b) when b contains any arithmetic */
+#  define MALLOC_MULTIPLY(a, b) \
+	malloc_multiply_check(a, b, sizeof(a), sizeof(size_t), __FILE__, __LINE__)
+#endif
+
+static inline size_t
+malloc_add_check(size_t a, size_t b, size_t sizeof_a, size_t sizeof_b,
+		 const char *fname, unsigned int linenum)
+{
+	/* the first sizeof-checks are intended to optimize away this entire
+	   if-check for types that are small enough to never wrap size_t. */
+	if ((sizeof_a >= sizeof(size_t) || sizeof_b >= sizeof(size_t)) &&
+	    SIZE_MAX - a < b) {
+		i_panic("file %s: line %d: memory allocation overflow: %zu + %zu",
+			fname, linenum, a, b);
+	}
+	return a + b;
+}
+#ifndef STATIC_CHECKER
+#  define MALLOC_ADD(a, b) \
+	malloc_add_check(a, b, sizeof(a), sizeof(b), __FILE__, __LINE__)
+#else
+/* avoid warning every time about sizeof(b) when b contains any arithmetic */
+#  define MALLOC_ADD(a, b) \
+	malloc_add_check(a, b, sizeof(a), sizeof(size_t), __FILE__, __LINE__)
+#endif
+
+#endif