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, 4 insertions, 1 deletions

diff --git a/src/xplist.c b/src/xplist.c
index 8f5cb15..3157ab0 100644
--- a/src/xplist.c
+++ b/src/xplist.c
@@ -192,7 +192,10 @@ static plist_err_t node_to_xml(node_t node, bytearray_t **outbuf, uint32_t depth
         tag = XPLIST_DATE;
         tag_len = XPLIST_DATE_LEN;
         {
-            Time64_T timev = (Time64_T)node_data->realval + MAC_EPOCH;
+            Time64_T timev;
+            if (plist_real_to_time64(node_data->realval, &timev) < 0) {
+                return PLIST_ERR_INVALID_ARG;
+            }
             struct TM _btime;
             struct TM *btime = gmtime64_r(&timev, &_btime);
             if (btime) {