common: validate PLIST_DATE values before Time64_T conversion

Avoid undefined behavior when serializing malformed PLIST_DATE values
containing NaN, infinity, or values outside the Time64_T range. Add a
shared helper for checked date conversion and use it across writer paths.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/common.c b/src/common.c
index 0b11d57..810c2e0 100644
--- a/src/common.c
+++ b/src/common.c
@@ -98,3 +98,18 @@ int num_digits_u(uint64_t i)
     return n;
 }
 #undef PO10u_LIMIT
+
+int plist_real_to_time64(double realval, Time64_T *timev)
+{
+    if (!timev || !isfinite(realval)) {
+        return -1;
+    }
+
+    if (realval < (double)TIME64_MIN - (double)MAC_EPOCH ||
+        realval > (double)TIME64_MAX - (double)MAC_EPOCH) {
+        return -1;
+    }
+
+    *timev = (Time64_T)realval + MAC_EPOCH;
+    return 0;
+}