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.

Author: nikias

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;
+}

src/common.h

@@ -22,11 +22,13 @@
 #define COMMON_H
 
 #include <stddef.h>
+#include "time64.h"
 
 #define MAC_EPOCH 978307200
 
 size_t dtostr(char *buf, size_t bufsize, double realval);
 int num_digits_i(int64_t i);
 int num_digits_u(uint64_t i);
+int plist_real_to_time64(double realval, Time64_T *timev);
 
 #endif

src/jplist.c

@@ -257,7 +257,10 @@ static plist_err_t node_to_json(node_t node, bytearray_t **outbuf, uint32_t dept
         break;
     case PLIST_DATE:
         if (coerce) {
-            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);
             char datebuf[32];

src/oplist.c

@@ -301,7 +301,10 @@ static plist_err_t node_to_openstep(node_t node, bytearray_t **outbuf, uint32_t
         break;
     case PLIST_DATE:
         if (coerce) {
-            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);
             char datebuf[32];

src/out-default.c

@@ -231,7 +231,10 @@ static plist_err_t node_to_string(node_t node, bytearray_t **outbuf, uint32_t de
         break;
     case PLIST_DATE:
         {
-            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) {

src/out-limd.c

@@ -220,7 +220,10 @@ static plist_err_t node_to_string(node_t node, bytearray_t **outbuf, uint32_t de
         break;
     case PLIST_DATE:
         {
-            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) {

src/out-plutil.c

@@ -237,7 +237,10 @@ static plist_err_t node_to_string(node_t node, bytearray_t **outbuf, uint32_t de
         break;
     case PLIST_DATE:
         {
-            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) {

src/time64.h

@@ -11,6 +11,13 @@ typedef long long       Int64;
 typedef Int64           Time64_T;
 typedef Int64           Year;
 
+#ifndef TIME64_MIN
+#define TIME64_MIN ((Time64_T)INT64_MIN)
+#endif
+
+#ifndef TIME64_MAX
+#define TIME64_MAX ((Time64_T)INT64_MAX)
+#endif
 
 /* A copy of the tm struct but with a 64 bit year */
 struct TM64 {

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) {