patch 8.0.0377: possible overflow when reading corrupted undo file

Problem:    Possible overflow when reading corrupted undo file.
Solution:   Check if allocated size is not too big. (King)

Author: brammool

src/undo.c

@@ -1787,7 +1787,7 @@ u_read_undo(char_u *name, char_u *hash, char_u *orig_name)
     linenr_T	line_lnum;
     colnr_T	line_colnr;
     linenr_T	line_count;
-    int		num_head = 0;
+    long	num_head = 0;
     long	old_header_seq, new_header_seq, cur_header_seq;
     long	seq_last, seq_cur;
     long	last_save_nr = 0;
@@ -1974,7 +1974,8 @@ u_read_undo(char_u *name, char_u *hash, char_u *orig_name)
      * When there are no headers uhp_table is NULL. */
     if (num_head > 0)
     {
-	uhp_table = (u_header_T **)U_ALLOC_LINE(
+	if (num_head < LONG_MAX / (long)sizeof(u_header_T *))
+	    uhp_table = (u_header_T **)U_ALLOC_LINE(
 					     num_head * sizeof(u_header_T *));
 	if (uhp_table == NULL)
 	    goto error;

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    377,
 /**/
     376,
 /**/