Fix unlikely lock file integer overflow

* src/filelock.c (within_one_second): Accept intmax_t first arg.
Avoid undefined behavior on integer overflow.
(current_lock_owner): Simplify based on within_one_second change.

(cherry picked from commit cbacdca9e3f6dcf9b88704391f06daf7301608b0)

diff --git a/src/filelock.c b/src/filelock.c
index 69bd0322d4cfbe0c24a4beeb0832ad6e8fd74ec4..55ab15feb8d3b2bc568ad8e25460df7029dfbbf7 100644 (file)
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -298,9 +298,10 @@ lock_file_1 (Lisp_Object lfname, bool force)
 /* Return true if times A and B are no more than one second apart.  */
 
 static bool
-within_one_second (time_t a, time_t b)
+within_one_second (intmax_t a, time_t b)
 {
-  return (a - b >= -1 && a - b <= 1);
+  intmax_t diff;
+  return !ckd_sub (&diff, a, b) && -1 <= diff && diff <= 1;
 }
 \f
 /* On systems lacking ELOOP, test for an errno value that shouldn't occur.  */
@@ -469,8 +470,7 @@ current_lock_owner (lock_info_type *owner, Lisp_Object lfname)
       else if (VALID_PROCESS_ID (pid)
                && (kill (pid, 0) >= 0 || errno == EPERM)
               && (boot_time == 0
-                  || (boot_time <= TYPE_MAXIMUM (time_t)
-                      && within_one_second (boot_time, get_boot_sec ()))))
+                  || within_one_second (boot_time, get_boot_sec ())))
         return ANOTHER_OWNS_IT;
       /* The owner process is dead or has a strange pid, so try to
          zap the lockfile.  */