PR fortran/95091 - Buffer overflows with submodules and long symbols

With submodules, name mangling results in long internal symbols.  This
requires adjustment of the sizes of temporaries to avoid buffer overflows.

2020-06-07  Harald Anlauf  <anlauf@gmx.de>

gcc/fortran/
	PR fortran/95091
	* class.c (get_unique_type_string, gfc_hash_value): Enlarge
	buffers, and check whether the strings returned by
	get_unique_type_string() fit.

(cherry picked from commit b342cfd648e6658363c7c8fef83af8f59dba1795)

gcc/fortran/class.c

@@ -509,9 +509,11 @@ get_unique_type_string (char *string, gfc_symbol *derived)
 static void
 get_unique_hashed_string (char *string, gfc_symbol *derived)
 {
-  /* Provide sufficient space to hold "symbol_Pdtsymbol".  */
-  char tmp[2*GFC_MAX_SYMBOL_LEN+5];
+  /* Provide sufficient space to hold "symbol.symbol_symbol".  */
+  char tmp[3*GFC_MAX_SYMBOL_LEN+3];
   get_unique_type_string (&tmp[0], derived);
+  size_t len = strnlen (tmp, sizeof (tmp));
+  gcc_assert (len < sizeof (tmp));
   /* If string is too long, use hash value in hex representation (allow for
      extra decoration, cf. gfc_build_class_symbol & gfc_find_derived_vtab).
      We need space to for 15 characters "__class_" + symbol name + "_%d_%da",
@@ -532,12 +534,13 @@ unsigned int
 gfc_hash_value (gfc_symbol *sym)
 {
   unsigned int hash = 0;
-  /* Provide sufficient space to hold "symbol_Pdtsymbol".  */
-  char c[2*GFC_MAX_SYMBOL_LEN+5];
+  /* Provide sufficient space to hold "symbol.symbol_symbol".  */
+  char c[3*GFC_MAX_SYMBOL_LEN+3];
   int i, len;
 
   get_unique_type_string (&c[0], sym);
-  len = strlen (c);
+  len = strnlen (c, sizeof (c));
+  gcc_assert (len < sizeof (c));
 
   for (i = 0; i < len; i++)
     hash = (hash << 6) + (hash << 16) - hash + c[i];

gcc/testsuite/gfortran.dg/pr95091.f90

+! { dg-do compile }
+! { dg-options "-fsecond-underscore" }
+! PR fortran/95091 - ICE in gfc_hash_value
+
+module m2345678901234567890123456789012345678901234567890123456789_123
+  type t2345678901234567890123456789012345678901234567890123456789_123
+  end type t2345678901234567890123456789012345678901234567890123456789_123
+  interface
+     module subroutine s2345678901234567890123456789012345678901234567890123456789_123 &
+          (x2345678901234567890123456789012345678901234567890123456789_123)
+    end
+  end interface
+end
+submodule(m2345678901234567890123456789012345678901234567890123456789_123) &
+     n2345678901234567890123456789012345678901234567890123456789_123
+  type, extends(t2345678901234567890123456789012345678901234567890123456789_123) :: &
+    u2345678901234567890123456789012345678901234567890123456789_123
+  end type
+end