Fix Bug 699660 "shading_param incomplete type checking"

Its possible to pass a t_struct parameter to .shfill which is not a
shading function built by .buildshading. This could then lead to memory
corruption or a segmentation fault by treating the object passed in
as if it were a shading.

Its non-trivial to check the t_struct, because this function can take
7 different kinds of structures as a parameter. Checking these is
possible, of course, but would add a performance penalty.

However, we can note that we never call .shfill without first calling
.buildshading, and we never call .buildshading without immediately
calling .shfill. So we can treat these as an atomic operation. The
.buildshading function takes all its parameters as PostScript objects
and validates them, so that should be safe.

This allows us to 'hide' the .shfill operator preventing the possibility
of passing an invalid parameter.

3 files changed, 9 insertions, 5 deletions

diff --git a/Resource/Init/gs_init.ps b/Resource/Init/gs_init.ps
index 5a5a42857..bc17d426e 100644
--- a/Resource/Init/gs_init.ps
+++ b/Resource/Init/gs_init.ps
@@ -2196,8 +2196,8 @@ SAFER { .setsafeglobal } if
 /.getiodevice /.getdevparms /.putdevparams /.bbox_transform /.matchmedia /.matchpagesize /.defaultpapersize
 /.oserrno /.setoserrno /.oserrorstring /.getCPSImode
 /.getscanconverter /.setscanconverter /.type1encrypt /.type1decrypt/.languagelevel /.setlanguagelevel /.eqproc /.fillpage /.buildpattern1 /.saslprep
-/.buildshading1 /.buildshadin2 /.buildshading3 /.buildshading4 /.buildshading5 /.buildshading6 /.buildshading7 /.buildshadingpattern
-/.argindex /.bytestring /.namestring /.stringbreak /.stringmatch /.globalvmarray /.globalvmdict /.globalvmpackedarray /.globalvmstring
+/.buildshading1 /.buildshading2 /.buildshading3 /.buildshading4 /.buildshading5 /.buildshading6 /.buildshading7 /.buildshadingpattern
+%/.shfill /.argindex /.bytestring /.namestring /.stringbreak /.stringmatch /.globalvmarray /.globalvmdict /.globalvmpackedarray /.globalvmstring
 /.localvmarray /.localvmdict /.localvmpackedarray /.localvmstring /.systemvmarray /.systemvmdict /.systemvmpackedarray /.systemvmstring /.systemvmfile /.systemvmlibfile
 /.systemvmSFD /.settrapparams /.currentsystemparams /.currentuserparams /.getsystemparam /.getuserparam /.setsystemparams /.setuserparams
 /.checkpassword /.locale_to_utf8 /.currentglobal /.gcheck /.imagepath
diff --git a/Resource/Init/gs_ll3.ps b/Resource/Init/gs_ll3.ps
index 5aa56a368..1d37e5361 100644
--- a/Resource/Init/gs_ll3.ps
+++ b/Resource/Init/gs_ll3.ps
@@ -440,6 +440,11 @@ systemdict /.reuseparamdict mark
     /shfill .systemvar /undefined signalerror
   } ifelse
 } bind def
+
+/.buildshading_and_shfill {
+  .buildshading .shfill
+} bind def
+
 systemdict /.reuseparamdict undef
 
 /.buildpattern2 {	% <template> <matrix> .buildpattern2
@@ -464,7 +469,7 @@ systemdict /.reuseparamdict undef
         % Currently, .shfill requires that the color space
         % in the pattern be the current color space.
         % Disable overprintmode for shfill
-  { dup gsave 0 .setoverprintmode .buildshading .shfill } stopped
+  { dup gsave 0 .setoverprintmode .buildshading_and_shfill } stopped
   grestore {
     /$error .systemvar /errorinfo 2 copy known {
       pop pop
diff --git a/Resource/Init/pdf_draw.ps b/Resource/Init/pdf_draw.ps
index b3d94ac1c..aef249df5 100644
--- a/Resource/Init/pdf_draw.ps
+++ b/Resource/Init/pdf_draw.ps
@@ -1365,9 +1365,8 @@ drawopdict begin
     { dup /.shading .knownget {
         exch pop
       } {
-       .buildshading
+       .buildshading_and_shfill
       } ifelse
-      .shfill
     } stopped {
       pop
       (   **** Error: Ignoring invalid smooth shading object, output may be incorrect.\n)