fs: Use safe math macros to prevent overflows

Replace direct arithmetic operations with macros from include/grub/safemath.h
to prevent potential overflow issues when calculating the memory sizes.

Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/fs/archelp.c

@@ -21,6 +21,7 @@
 #include <grub/fs.h>
 #include <grub/disk.h>
 #include <grub/dl.h>
+#include <grub/safemath.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
@@ -68,6 +69,7 @@ handle_symlink (struct grub_archelp_data *data,
   char *rest;
   char *linktarget;
   grub_size_t linktarget_len;
+  grub_size_t sz;
 
   *restart = 0;
 
@@ -98,7 +100,12 @@ handle_symlink (struct grub_archelp_data *data,
   if (linktarget[0] == '\0')
     return GRUB_ERR_NONE;
   linktarget_len = grub_strlen (linktarget);
-  target = grub_malloc (linktarget_len + grub_strlen (*name) + 2);
+
+  if (grub_add (linktarget_len, grub_strlen (*name), &sz) ||
+      grub_add (sz, 2, &sz))
+    return grub_error (GRUB_ERR_OUT_OF_RANGE, N_("link target length overflow"));
+
+  target = grub_malloc (sz);
   if (!target)
     return grub_errno;