lstab: Don't free lstab on update.

The modification timestamp of the leapfile is checked with every
call of lstab_utc2tai(). If the file is modified, the provided lstab
structure is freed and a new one is allocated from the updated leapfile.
But the new lstab is not returned to the caller as the function doesn't
accept a pointer to the pointer to lstab. This causes reading from the
freed memory and leak of the newly allocated memory.

Modify update_leapsecond_table() to read the updated leapfile into the
existing lstab structure instead of the reallocation.

Signed-off-by: Miroslav Lichvar <[email protected]>

lstab.c

@@ -195,7 +195,6 @@ struct lstab *lstab_create(const char *filename)
 
 int update_leapsecond_table(struct lstab *lstab)
 {
-	const char* leapfile;
 	struct stat statbuf;
 	int err;
 
@@ -212,14 +211,14 @@ int update_leapsecond_table(struct lstab *lstab)
 		return 0;
 	}
 	printf("updating leap seconds file\n");
-	leapfile = lstab->leapfile;
-	lstab_destroy(lstab);
 
-	lstab = lstab_create(leapfile);
-	if (!lstab) {
+	if (lstab_read(lstab, lstab->leapfile)) {
+		lstab->length = 0;
 		return -1;
 	}
 
+	lstab->lsfile_mtime = statbuf.st_mtim.tv_sec;
+
 	return 0;
 }