The following patch was adapted for GNU Ghostscript
by Mark H Weaver <mhw@netris.org> based on:

http://git.ghostscript.com/?p=ghostpdl.git;a=commit;h=6d444c273da5499a4cd72f21cb6d4c9a5256807d

From 6d444c273da5499a4cd72f21cb6d4c9a5256807d Mon Sep 17 00:00:00 2001
From: Chris Liddell <chris.liddell@artifex.com>
Date: Wed, 5 Oct 2016 09:55:55 +0100
Subject: [PATCH] Bug 697178: Add a file permissions callback

For the rare occasions when the graphics library directly opens a file
(currently for reading), this allows us to apply any restrictions on
file access normally applied in the interpteter.
---
 base/gsicc_manage.c | 10 ++++++----
 base/gslibctx.c     | 12 +++++++++++-
 base/gslibctx.h     |  7 +++++++
 psi/imain.c         |  2 ++
 psi/int.mak         |  2 +-
 psi/zfile.c         | 19 +++++++++++++++++++
 psi/zfile.h         |  7 +++++++
 7 files changed, 53 insertions(+), 6 deletions(-)

diff --git a/base/gsicc_manage.c b/base/gsicc_manage.c
index 931c2a6..e9c09c3 100644
--- a/base/gsicc_manage.c
+++ b/base/gsicc_manage.c
@@ -1028,10 +1028,12 @@ gsicc_open_search(const char* pname, int namelen, gs_memory_t *mem_gc,
     }
 
     /* First just try it like it is */
-    str = sfopen(pname, "rb", mem_gc);
-    if (str != NULL) {
-        *strp = str;
-        return 0;
+    if (gs_check_file_permission(mem_gc, pname, namelen, "r") >= 0) {
+        str = sfopen(pname, "rb", mem_gc);
+        if (str != NULL) {
+            *strp = str;
+            return 0;
+        }
     }
 
     /* If that fails, try %rom% */ /* FIXME: Not sure this is needed or correct */
diff --git a/base/gslibctx.c b/base/gslibctx.c
index eaa0458..37ce1ca 100644
--- a/base/gslibctx.c
+++ b/base/gslibctx.c
@@ -121,7 +121,7 @@ int gs_lib_ctx_init( gs_memory_t *mem )
         mem->gs_lib_ctx = NULL;
         return -1;
     }
- 
+    pio->client_check_file_permission = NULL;
     gp_get_realtime(pio->real_time_0);
 
     return 0;
@@ -262,3 +262,13 @@ void errflush(const gs_memory_t *mem)
         fflush(mem->gs_lib_ctx->fstderr);
     /* else nothing to flush */
 }
+
+int
+gs_check_file_permission (gs_memory_t *mem, const char *fname, const int len, const char *permission)
+{
+    int code = 0;
+    if (mem->gs_lib_ctx->client_check_file_permission != NULL) {
+        code = mem->gs_lib_ctx->client_check_file_permission(mem, fname, len, permission);
+    }
+    return code;
+}
diff --git a/base/gslibctx.h b/base/gslibctx.h
index 7a4e110..020e2d9 100644
--- a/base/gslibctx.h
+++ b/base/gslibctx.h
@@ -32,6 +32,9 @@ typedef struct gs_fapi_server_s gs_fapi_server;
 #  define gs_font_dir_DEFINED
 typedef struct gs_font_dir_s gs_font_dir;
 #endif
+
+typedef int (*client_check_file_permission_t) (gs_memory_t *mem, const char *fname, const int len, const char *permission);
+
 typedef struct gs_lib_ctx_s
 {
     gs_memory_t *memory;  /* mem->gs_lib_ctx->memory == mem */
@@ -59,6 +62,7 @@ typedef struct gs_lib_ctx_s
     bool dict_auto_expand;  /* ps dictionary: false level 1 true level 2 or 3 */
     /* A table of local copies of the IODevices */
     struct gx_io_device_s **io_device_table;
+    client_check_file_permission_t client_check_file_permission;
     /* Define the default value of AccurateScreens that affects setscreen
        and setcolorscreen. */
     bool screen_accurate_screens;
@@ -108,6 +112,9 @@ int
 void gs_lib_ctx_set_icc_directory(const gs_memory_t *mem_gc, const char* pname,
                         int dir_namelen);
 
+int
+gs_check_file_permission (gs_memory_t *mem, const char *fname, const int len, const char *permission);
+
 #define IS_LIBCTX_STDOUT(mem, f) (f == mem->gs_lib_ctx->fstdout)
 #define IS_LIBCTX_STDERR(mem, f) (f == mem->gs_lib_ctx->fstderr)
 
diff --git a/psi/imain.c b/psi/imain.c
index 9a9bb5d..6874128 100644
--- a/psi/imain.c
+++ b/psi/imain.c
@@ -57,6 +57,7 @@
 #include "ivmspace.h"
 #include "idisp.h"              /* for setting display device callback */
 #include "iplugin.h"
+#include "zfile.h"
 
 #ifdef PACIFY_VALGRIND
 #include "valgrind.h"
@@ -215,6 +216,7 @@ gs_main_init1(gs_main_instance * minst)
                                            "the_gs_name_table");
             if (code < 0)
                 return code;
+            mem->gs_lib_ctx->client_check_file_permission = z_check_file_permissions;
         }
         code = obj_init(&minst->i_ctx_p, &idmem);  /* requires name_init */
         if (code < 0)
diff --git a/psi/int.mak b/psi/int.mak
index 4654afc..bb30d51 100644
--- a/psi/int.mak
+++ b/psi/int.mak
@@ -1868,7 +1868,7 @@ $(PSOBJ)imain.$(OBJ) : $(PSSRC)imain.c $(GH) $(memory__h) $(string__h)\
  $(ialloc_h) $(iconf_h) $(idebug_h) $(idict_h) $(idisp_h) $(iinit_h)\
  $(iname_h) $(interp_h) $(iplugin_h) $(isave_h) $(iscan_h) $(ivmspace_h)\
  $(iinit_h) $(main_h) $(oper_h) $(ostack_h)\
- $(sfilter_h) $(store_h) $(stream_h) $(strimpl_h)
+ $(sfilter_h) $(store_h) $(stream_h) $(strimpl_h) $(zfile_h)
 	$(PSCC) $(PSO_)imain.$(OBJ) $(C_) $(PSSRC)imain.c
 
 #****** $(CCINT) interp.c
diff --git a/psi/zfile.c b/psi/zfile.c
index 2c6c958..2f27f82 100644
--- a/psi/zfile.c
+++ b/psi/zfile.c
@@ -197,6 +197,25 @@ check_file_permissions(i_ctx_t *i_ctx_p, const char *fname, int len,
     return check_file_permissions_reduced(i_ctx_p, fname_reduced, rlen, permitgroup);
 }
 
+/* z_check_file_permissions: see zfile.h for explanation
+ */
+int
+z_check_file_permissions(gs_memory_t *mem, const char *fname, const int len, const char *permission)
+{
+    i_ctx_t *i_ctx_p = get_minst_from_memory(mem)->i_ctx_p;
+    gs_parsed_file_name_t pname;
+    const char *permitgroup = permission[0] == 'r' ? "PermitFileReading" : "PermitFileWriting";
+    int code = gs_parse_file_name(&pname, fname, len, imemory);
+    if (code < 0)
+        return code;
+
+    if (pname.iodev && i_ctx_p->LockFilePermissions && strcmp(pname.iodev->dname, "%pipe%") == 0)
+        return e_invalidfileaccess;
+        
+    code = check_file_permissions(i_ctx_p, fname, len, permitgroup);
+    return code;
+}
+
 /* <name_string> <access_string> file <file> */
 int                             /* exported for zsysvm.c */
 zfile(i_ctx_t *i_ctx_p)
diff --git a/psi/zfile.h b/psi/zfile.h
index fdf1373..a9399c7 100644
--- a/psi/zfile.h
+++ b/psi/zfile.h
@@ -22,4 +22,11 @@
 int zopen_file(i_ctx_t *i_ctx_p, const gs_parsed_file_name_t *pfn,
            const char *file_access, stream **ps, gs_memory_t *mem);
 
+/* z_check_file_permissions: a callback (via mem->gs_lib_ctx->client_check_file_permission)
+ * to allow applying the above permissions checks when opening file(s) from
+ * the graphics library
+ */
+int
+z_check_file_permissions(gs_memory_t *mem, const char *fname,
+                                 const int len, const char *permission);
 #endif
-- 
2.9.1

