Make sure cmp_time() doesn't mess up due to a time_t overflow.

Fixes bug 10643.

2 files changed, 11 insertions, 7 deletions

diff --git a/NEWS b/NEWS
index 9ad83068..a65b3bb3 100644
--- a/NEWS
+++ b/NEWS
@@ -104,6 +104,9 @@ Changes since 3.1.0:
       inc-recursive copy that is preserving directory times. e.g. using
       --omit-dir-times will avoid these early directories being created.
 
+    - Fix a bug in cmp_time() that would return a wrong result if the 2 times
+      differed by an amount greater than what a time_t can hold.
+
   DEVELOPER RELATED:
 
     - We now include an example systemd file (in packaging/systemd).
diff --git a/util.c b/util.c
index bd537ae9..05aa86a0 100644
--- a/util.c
+++ b/util.c
@@ -1325,16 +1325,17 @@ char *timestring(time_t t)
 int cmp_time(time_t file1, time_t file2)
 {
 	if (file2 > file1) {
-		if (file2 - file1 <= modify_window)
-			return 0;
-		return -1;
+		/* The final comparison makes sure that modify_window doesn't overflow a
+		 * time_t, which would mean that file2 must be in the equality window. */
+		if (!modify_window || (file2 > file1 + modify_window && file1 + modify_window > file1))
+			return -1;
+	} else if (file1 > file2) {
+		if (!modify_window || (file1 > file2 + modify_window && file2 + modify_window > file2))
+			return 1;
 	}
-	if (file1 - file2 <= modify_window)
-		return 0;
-	return 1;
+	return 0;
 }
 
-
 #ifdef __INSURE__XX
 #include <dlfcn.h>