allocations: test for overflow of requested size

Introduce some helper macros to test integer overflow from arithmetic
and set error message appropriately.

1 files changed, 22 insertions, 0 deletions

diff --git a/src/common.h b/src/common.h
index 4b4a99775..b53798eaf 100644
--- a/src/common.h
+++ b/src/common.h
@@ -174,6 +174,28 @@ GIT_INLINE(void) git__init_structure(void *structure, size_t len, unsigned int v
 	GITERR_CHECK_VERSION(&(VERSION), _tmpl.version, #TYPE);	\
 	memcpy((PTR), &_tmpl, sizeof(_tmpl)); } while (0)
 
+/** Check for integer overflow from addition or multiplication */
+#define GIT_ALLOC_OVERFLOW_ADD(one, two) \
+	((one) + (two) < (one))
+
+/** Check for integer overflow from multiplication */
+#define GIT_ALLOC_OVERFLOW_MULTIPLY(one, two) \
+	(one && ((one) * (two)) / (one) != (two))
+
+/** Check for additive overflow, failing if it would occur. */
+#define GITERR_CHECK_ALLOC_ADD(one, two) \
+	if (GIT_ALLOC_OVERFLOW_ADD(one, two)) { \
+		giterr_set_oom(); \
+		return -1; \
+	}
+
+/** Check for multiplicative overflow, failing if it would occur. */
+#define GITERR_CHECK_ALLOC_MULTIPLY(nelem, elsize) \
+	if (GIT_ALLOC_OVERFLOW_MULTIPLY(nelem, elsize)) { \
+		giterr_set_oom(); \
+		return -1; \
+	}
+
 /* NOTE: other giterr functions are in the public errors.h header file */
 
 #include "util.h"