[psaux] Fix segfault.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10768

* src/psaux/cffdecode.c (cff_decoder_parse_charstrings)
<cff_op_callothersubr> [CFF_CONFIG_OPTION_OLD_ENGINE]: Check
argument.

ChangeLog

@@ -1,11 +1,23 @@
 2018-10-02  Werner Lemberg  <wl@gnu.org>
 
-	[psaux] Fix numeric overflow.
+	[psaux] Fix segfault.
 
 	Reported as
 
 	  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10768
 
+	* src/psaux/cffdecode.c (cff_decoder_parse_charstrings)
+	<cff_op_callothersubr> [CFF_CONFIG_OPTION_OLD_ENGINE]: Check
+	argument.
+
+2018-10-02  Werner Lemberg  <wl@gnu.org>
+
+	[psaux] Fix numeric overflow.
+
+	Reported as
+
+	  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10740
+
 	* src/psaux/cffdecode.c (cff_decoder_parse_charstrings) <cff_op_roll>
 	[CFF_CONFIG_OPTION_OLD_ENGINE]: Use NEG_INT.
 

src/psaux/cffdecode.c

@@ -2027,20 +2027,31 @@
           break;
 
         case cff_op_callothersubr:
-          /* this is an invalid Type 2 operator; however, there        */
-          /* exist fonts which are incorrectly converted from probably */
-          /* Type 1 to CFF, and some parsers seem to accept it         */
+          {
+            FT_Fixed  arg;
 
-          FT_TRACE4(( " callothersubr (invalid op)\n" ));
 
-          /* subsequent `pop' operands should add the arguments,       */
-          /* this is the implementation described for `unknown' other  */
-          /* subroutines in the Type1 spec.                            */
-          /*                                                           */
-          /* XXX Fix return arguments (see discussion below).          */
-          args -= 2 + ( args[-2] >> 16 );
-          if ( args < stack )
-            goto Stack_Underflow;
+            /* this is an invalid Type 2 operator; however, there      */
+            /* exist fonts which are incorrectly converted from        */
+            /* probably Type 1 to CFF, and some parsers seem to accept */
+            /* it                                                      */
+
+            FT_TRACE4(( " callothersubr (invalid op)\n" ));
+
+            /* subsequent `pop' operands should add the arguments,     */
+            /* this is the implementation described for `unknown'      */
+            /* other subroutines in the Type1 spec.                    */
+            /*                                                         */
+            /* XXX Fix return arguments (see discussion below).        */
+
+            arg = 2 + ( args[-2] >> 16 );
+            if ( arg >= CFF_MAX_OPERANDS )
+              goto Stack_Underflow;
+
+            args -= arg;
+            if ( args < stack )
+              goto Stack_Underflow;
+          }
           break;
 
         case cff_op_pop: