[Forensics-changes] [yara] 144/192: Fix undefined behavior in hash (#642)

[Hilko Bengen]

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bengen pushed a commit to annotated tag v3.6.0
in repository yara.

commit 7fd1330917573bf7074bd366eee0792bbdd8bbcf
Author: Nate Rosenblum <flander at gmail.com>
Date:   Thu Apr 20 12:07:52 2017 -0700

    Fix undefined behavior in hash (#642)
    
    The previous rotation implementation invoked undefined behavior for
    every index in the target string where i % 32 == 0. Found via ASan.
    
    Fixes #641
---
 libyara/hash.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libyara/hash.c b/libyara/hash.c
index b515677..776d96c 100644
--- a/libyara/hash.c
+++ b/libyara/hash.c
@@ -35,9 +35,15 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <yara/mem.h>
 #include <yara/error.h>
 
-#define ROTATE_INT32(x, shift) \
-    ((x << (shift % 32)) | (x >> (32 - (shift % 32))))
+// Constant-time left rotate that does not invoke undefined behavior.
+// http://blog.regehr.org/archives/1063
+uint32_t rotl32(uint32_t x, uint32_t shift) {
+  assert(shift < 32);
+  return (x << shift) | (x >> (-shift & 31));
+}
 
+#define ROTATE_INT32(x, shift) \
+    rotl32(x, shift % 32)
 
 uint32_t byte_to_int32[]  =
 {

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