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path: root/seccomp.patch
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diff -Naur mupdf-1.11-source/Makefile mupdf/Makefile
--- mupdf-1.11-source/Makefile	2017-04-05 13:02:21.000000000 +0200
+++ mupdf/Makefile	2017-08-20 13:59:29.260759115 +0200
@@ -16,6 +16,12 @@
 # set a variable that was set on the command line.
 CFLAGS += $(XCFLAGS) -Iinclude -Igenerated
 LIBS += $(XLIBS) -lm
+LIBS += -lseccomp
+
+# please note: rules set in makerules do not work yet.
+# HAVE_LIBSECCOMP should be defined here
+# todo: implement protectedView option
+# and additional mupdf-x11-sandbox binary should be created for protectedView
 
 LIBS += $(FREETYPE_LIBS)
 LIBS += $(HARFBUZZ_LIBS)
@@ -34,6 +40,7 @@
 CFLAGS += $(JPEGXR_CFLAGS)
 CFLAGS += $(LIBCRYPTO_CFLAGS)
 CFLAGS += $(LIBJPEG_CFLAGS)
+CFLAGS += $(LIBSECCOMP_CFLAGS)
 CFLAGS += $(LURATECH_CFLAGS)
 CFLAGS += $(MUJS_CFLAGS)
 CFLAGS += $(OPENJPEG_CFLAGS)
@@ -344,14 +351,14 @@
 
 ifeq "$(HAVE_X11)" "yes"
 MUVIEW_X11_EXE := $(OUT)/mupdf-x11
-MUVIEW_X11_OBJ := $(addprefix $(OUT)/platform/x11/, x11_main.o x11_image.o pdfapp.o)
+MUVIEW_X11_OBJ := $(addprefix $(OUT)/platform/x11/, x11_main.o libsec.o x11_image.o pdfapp.o)
 $(MUVIEW_X11_OBJ) : $(FITZ_HDR) $(PDF_HDR)
 $(MUVIEW_X11_EXE) : $(MUVIEW_X11_OBJ) $(MUPDF_LIB) $(THIRD_LIB)
 	$(LINK_CMD) $(X11_LIBS)
 
 ifeq "$(HAVE_CURL)" "yes"
 MUVIEW_X11_CURL_EXE := $(OUT)/mupdf-x11-curl
-MUVIEW_X11_CURL_OBJ := $(addprefix $(OUT)/platform/x11/curl/, x11_main.o x11_image.o pdfapp.o curl_stream.o)
+MUVIEW_X11_CURL_OBJ := $(addprefix $(OUT)/platform/x11/curl/, x11_main.o libsec.o x11_image.o pdfapp.o curl_stream.o)
 $(MUVIEW_X11_CURL_OBJ) : $(FITZ_HDR) $(PDF_HDR)
 $(MUVIEW_X11_CURL_EXE) : $(MUVIEW_X11_CURL_OBJ) $(MUPDF_LIB) $(THIRD_LIB) $(CURL_LIB)
 	$(LINK_CMD) $(X11_LIBS) $(CURL_LIBS) $(SYS_CURL_DEPS)
diff -Naur mupdf-1.11-source/Makerules mupdf/Makerules
--- mupdf-1.11-source/Makerules	2017-04-05 13:02:21.000000000 +0200
+++ mupdf/Makerules	2017-08-20 13:57:17.007431507 +0200
@@ -155,6 +155,12 @@
 SYS_OPENJPEG_LIBS := $(shell pkg-config --libs libopenjp2)
 endif
 
+ifeq "$(shell pkg-config --exists libseccomp && echo yes)" "yes"
+HAVE_LIBSECCOMP = yes
+SYS_LIBSECCOMP_CFLAGS = $(shell pkg-config --cflags libseccomp)
+SYS_LIBSECCOMP_LIBS = $(shell pkg-config --libs libseccomp)
+endif
+
 SYS_JBIG2DEC_LIBS := -ljbig2dec
 SYS_LIBJPEG_LIBS := -ljpeg
 SYS_ZLIB_LIBS := -lz
@@ -279,3 +285,8 @@
 HAVE_X11 ?= no
 HAVE_GLFW ?= no
 endif
+
+ifeq "$(HAVE_PTHREADS)" "yes"
+CFLAGS += -DHAVE_PTHREADS
+LIBS += -lpthread
+endif
diff -Naur mupdf-1.11-source/Makethird mupdf/Makethird
--- mupdf-1.11-source/Makethird	2017-04-05 13:02:21.000000000 +0200
+++ mupdf/Makethird	2017-08-20 14:00:35.777422904 +0200
@@ -721,3 +721,10 @@
 PTHREAD_CFLAGS := $(SYS_PTHREAD_CFLAGS)
 PTHREAD_LIBS := $(SYS_PTHREAD_LIBS)
 #endif
+
+# --- libSeccomp ---
+
+ifeq "$(HAVE_LIBSECCOMP)" "yes"
+LIBSECCOMP_CFLAGS := $(SYS_LIBSECCOMP_CFLAGS)
+LIBSECCOMP_LIBS := $(SYS_LIBSECCOMP_LIBS)
+endif
diff -Naur mupdf-1.11-source/platform/x11/libsec.c mupdf/platform/x11/libsec.c
--- mupdf-1.11-source/platform/x11/libsec.c	1970-01-01 01:00:00.000000000 +0100
+++ mupdf/platform/x11/libsec.c	2017-10-28 17:17:23.053794622 +0200
@@ -0,0 +1,501 @@
+#include "libsec.h"
+#include <stdio.h>
+
+#define HAVE_LIBSECCOMP
+#ifdef HAVE_LIBSECCOMP
+
+#include <seccomp.h> /* libseccomp */
+#include <sys/prctl.h> /* prctl */
+#include <sys/socket.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#define DENY_RULE(call) { if (seccomp_rule_add (ctx, SCMP_ACT_KILL, SCMP_SYS(call), 0) < 0) goto out; }
+#define ALLOW_RULE(call) { if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(call), 0) < 0) goto out; }
+
+scmp_filter_ctx ctx;
+
+
+int protectedMode(void){
+
+    // prevent child processes from getting more priv e.g. via setuid, capabilities, ...
+    //prctl(PR_SET_NO_NEW_PRIVS, 1);
+
+    if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+        perror("prctl SET_NO_NEW_PRIVS");
+        exit(EXIT_FAILURE);
+    }
+
+
+    // prevent escape via ptrace
+    //prctl(PR_SET_DUMPABLE, 0);
+
+    if(prctl (PR_SET_DUMPABLE, 0, 0, 0, 0)){
+        perror("prctl PR_SET_DUMPABLE");
+        exit(EXIT_FAILURE);
+    }
+
+
+    // initialize the filter
+    ctx = seccomp_init(SCMP_ACT_ALLOW);
+    if (ctx == NULL)
+        return 1;
+
+    DENY_RULE (_sysctl);
+    DENY_RULE (acct);
+    DENY_RULE (add_key);
+    DENY_RULE (adjtimex);
+    DENY_RULE (chroot);
+    DENY_RULE (clock_adjtime);
+    DENY_RULE (create_module);
+    DENY_RULE (delete_module);
+    DENY_RULE (fanotify_init);
+    DENY_RULE (finit_module);
+    DENY_RULE (get_kernel_syms);
+    DENY_RULE (get_mempolicy);
+    DENY_RULE (init_module);
+    DENY_RULE (io_cancel);
+    DENY_RULE (io_destroy);
+    DENY_RULE (io_getevents);
+    DENY_RULE (io_setup);
+    DENY_RULE (io_submit);
+    DENY_RULE (ioperm);
+    DENY_RULE (iopl);
+    DENY_RULE (ioprio_set);
+    DENY_RULE (kcmp);
+    DENY_RULE (kexec_file_load);
+    DENY_RULE (kexec_load);
+    DENY_RULE (keyctl);
+    DENY_RULE (lookup_dcookie);
+    DENY_RULE (mbind);
+    DENY_RULE (nfsservctl);
+    DENY_RULE (migrate_pages);
+    DENY_RULE (modify_ldt);
+    DENY_RULE (mount);
+    DENY_RULE (move_pages);
+    DENY_RULE (name_to_handle_at);
+    DENY_RULE (open_by_handle_at);
+    DENY_RULE (perf_event_open);
+    DENY_RULE (pivot_root);
+    DENY_RULE (process_vm_readv);
+    DENY_RULE (process_vm_writev);
+    DENY_RULE (ptrace);
+    DENY_RULE (reboot);
+    DENY_RULE (remap_file_pages);
+    DENY_RULE (request_key);
+    DENY_RULE (set_mempolicy);
+    DENY_RULE (swapoff);
+    DENY_RULE (swapon);
+    DENY_RULE (sysfs);
+    DENY_RULE (syslog);
+    DENY_RULE (tuxcall);
+    DENY_RULE (umount2);
+    DENY_RULE (uselib);
+    DENY_RULE (vmsplice);
+
+    //applying filter...
+    if (seccomp_load (ctx) >= 0){
+	// free ctx after the filter has been loaded into the kernel
+	seccomp_release(ctx);
+        return 0;
+    }
+    
+  out:
+    //something went wrong
+    //printf("something went wrong\n");
+    seccomp_release(ctx);
+    return 1;
+}
+
+
+int protectedView(void){
+
+    // prevent child processes from getting more priv e.g. via setuid, capabilities, ...
+    //prctl(PR_SET_NO_NEW_PRIVS, 1);
+
+    if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+        perror("prctl SET_NO_NEW_PRIVS");
+        exit(EXIT_FAILURE);
+    }
+
+
+    // prevent escape via ptrace
+    //prctl(PR_SET_DUMPABLE, 0);
+
+    if(prctl (PR_SET_DUMPABLE, 0, 0, 0, 0)){
+        perror("prctl PR_SET_DUMPABLE");
+        exit(EXIT_FAILURE);
+    }
+
+    
+    // initialize the filter
+    ctx = seccomp_init(SCMP_ACT_KILL);
+    if (ctx == NULL)
+        return 1;
+
+
+    ALLOW_RULE (access);
+    ALLOW_RULE (brk);
+    ALLOW_RULE (clock_gettime);
+    ALLOW_RULE (close);
+    ALLOW_RULE (connect);
+    ALLOW_RULE (exit);
+    ALLOW_RULE (exit_group);
+    ALLOW_RULE (fcntl);  /* not specified below */
+    ALLOW_RULE (fstat);
+    ALLOW_RULE (futex);
+    ALLOW_RULE (getpeername);
+    ALLOW_RULE (getrlimit);
+    ALLOW_RULE (getsockname);
+    ALLOW_RULE (getsockopt);  /* needed for access to x11 socket in network namespace (without abstract sockets) */
+    ALLOW_RULE (lseek);
+    ALLOW_RULE (mmap);
+    ALLOW_RULE (mprotect);
+    ALLOW_RULE (mremap);
+    ALLOW_RULE (munmap);
+    //ALLOW_RULE (open);  /* specified below */
+    //ALLOW_RULE (openat);  /* specified below */
+    ALLOW_RULE (prctl);
+    ALLOW_RULE (poll);
+    ALLOW_RULE (read);
+    ALLOW_RULE (recvfrom);
+    ALLOW_RULE (recvmsg);
+    ALLOW_RULE (restart_syscall);
+    ALLOW_RULE (rt_sigaction);
+    ALLOW_RULE (seccomp);
+    ALLOW_RULE (select);
+    ALLOW_RULE (shmat);
+    ALLOW_RULE (shmctl);
+    ALLOW_RULE (shmget);
+    ALLOW_RULE (shutdown);
+    ALLOW_RULE (stat);
+    //ALLOW_RULE (socket);  /* specified below */
+    ALLOW_RULE (sysinfo);
+    ALLOW_RULE (uname);
+    //ALLOW_RULE (write);  /* specified below */
+    ALLOW_RULE (writev);  /* not specified below */
+    ALLOW_RULE (wait4);  /* trying to open links should not crash the app */
+
+    
+	/* special restrictions for socket, only allow AF_UNIX/AF_LOCAL */
+	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
+	                      SCMP_CMP(0, SCMP_CMP_EQ, AF_UNIX)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
+	                      SCMP_CMP(0, SCMP_CMP_EQ, AF_LOCAL)) < 0)
+		goto out;
+
+
+	/* special restrictions for open, prevent opening files for writing */
+	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY | O_RDWR, 0)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ERRNO (EACCES), SCMP_SYS(open), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ERRNO (EACCES), SCMP_SYS(open), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) < 0)
+		goto out;
+
+
+	/* special restrictions for openat, prevent opening files for writing */
+	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(openat), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY | O_RDWR, 0)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ERRNO (EACCES), SCMP_SYS(openat), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ERRNO (EACCES), SCMP_SYS(openat), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) < 0)
+		goto out;
+
+
+
+
+    // ------------ experimental filters ---------------
+
+
+
+
+    /* this filter is susceptible to TOCTOU race conditions, providing limited use */
+    /* allow opening only specified files identified by their file descriptors*/
+
+    // this requires either a list of all files to open (A LOT!!!)
+    // or needs to be applied only after initialisation, right before parsing
+    // if(seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(read), 1,
+    //                         SCMP_CMP(SCMP_CMP_EQ, fd)) < 0) // or < 1 ???
+    //     goto out;
+
+
+    /* restricting write access */
+
+    /* allow stdin */
+    // if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
+    //                         SCMP_CMP(0, SCMP_CMP_EQ, 0)) < 0 )
+    //     goto out;
+
+    /* allow stdout */
+    // if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
+    //                             SCMP_CMP(0, SCMP_CMP_EQ, 1)) < 0 )
+    //     goto out;
+
+    /* allow stderr */
+    if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
+                                 SCMP_CMP(0, SCMP_CMP_EQ, 2)) < 0 )
+        goto out;
+
+
+    /* restrict writev (write a vector) access */
+    // this does not seem reliable but it surprisingly is. investigate more
+    //if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(writev), 1,
+    //                            SCMP_CMP(0, SCMP_CMP_EQ, 3)) < 0 )
+    //    goto out;
+
+    //test if repeating this after some time or denying it works
+
+
+    // firest attempt to filter poll requests
+    // if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(poll), 1,
+    // 	                      SCMP_CMP(0, SCMP_CMP_MASKED_EQ, POLLIN | POLL, 0)) < 0)
+    // 	goto out;
+
+
+    /* restrict fcntl calls */
+    // this syscall sets the file descriptor to read write
+    //if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fcntl), 1,
+    //                            SCMP_CMP(0, SCMP_CMP_EQ, 3)) < 0 )
+    //    goto out;
+    // fcntl(3, F_GETFL)                       = 0x2 (flags O_RDWR)
+    // fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
+    // fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
+
+
+
+
+    // ------------------ end of experimental filters ------------------
+
+    //applying filter...
+    if (seccomp_load (ctx) >= 0){
+	// free ctx after the filter has been loaded into the kernel
+	seccomp_release(ctx);
+        return 0;
+    }
+
+ out:
+    //something went wrong
+    seccomp_release(ctx);
+    return 1;
+}
+
+int renderFilter(void){
+
+    // prevent child processes from getting more priv e.g. via setuid, capabilities, ...
+    //prctl(PR_SET_NO_NEW_PRIVS, 1);
+
+    if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+        perror("prctl SET_NO_NEW_PRIVS");
+        exit(EXIT_FAILURE);
+    }
+
+
+    // prevent escape via ptrace
+    //prctl(PR_SET_DUMPABLE, 0);
+
+    if(prctl (PR_SET_DUMPABLE, 0, 0, 0, 0)){
+        perror("prctl PR_SET_DUMPABLE");
+        exit(EXIT_FAILURE);
+    }
+
+    
+    // initialize the filter
+    ctx = seccomp_init(SCMP_ACT_KILL);
+    if (ctx == NULL)
+        return 1;
+
+
+    ALLOW_RULE (access);
+    ALLOW_RULE (brk);
+    ALLOW_RULE (clock_gettime);
+    ALLOW_RULE (close);
+    //ALLOW_RULE (connect);
+    ALLOW_RULE (exit);
+    ALLOW_RULE (exit_group);
+    ALLOW_RULE (fcntl);  /* not specified below */
+    ALLOW_RULE (fstat);
+    ALLOW_RULE (futex);
+    ALLOW_RULE (getpeername);
+    ALLOW_RULE (getrlimit);
+    //ALLOW_RULE (getsockname);
+    //ALLOW_RULE (getsockopt); 
+    ALLOW_RULE (lseek);
+    ALLOW_RULE (mmap);
+    ALLOW_RULE (mprotect);
+    ALLOW_RULE (mremap);
+    ALLOW_RULE (munmap);
+    //ALLOW_RULE (open);  /* specified below */
+    //ALLOW_RULE (openat);  /* specified below */
+    ALLOW_RULE (poll);
+    ALLOW_RULE (read);
+    ALLOW_RULE (recvfrom);
+    ALLOW_RULE (recvmsg);
+    ALLOW_RULE (restart_syscall);
+    ALLOW_RULE (rt_sigaction);
+    ALLOW_RULE (select);
+    ALLOW_RULE (shmat);
+    ALLOW_RULE (shmctl);
+    ALLOW_RULE (shmget);
+    ALLOW_RULE (shutdown);
+    ALLOW_RULE (stat);
+    //ALLOW_RULE (socket);
+    ALLOW_RULE (sysinfo);
+    ALLOW_RULE (uname);
+    //ALLOW_RULE (write);  /* specified below */
+    ALLOW_RULE (writev);  /* not specified below */
+    ALLOW_RULE (wait4);  /* trying to open links should not crash the app */
+
+    
+	/* special restrictions for socket, only allow AF_UNIX/AF_LOCAL */
+    //	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
+    //	                      SCMP_CMP(0, SCMP_CMP_EQ, AF_UNIX)) < 0)
+    //		goto out;
+
+    //	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
+    //	                      SCMP_CMP(0, SCMP_CMP_EQ, AF_LOCAL)) < 0)
+    //		goto out;
+
+
+	/* special restrictions for open, prevent opening files for writing */
+	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY | O_RDWR, 0)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ERRNO (EACCES), SCMP_SYS(open), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ERRNO (EACCES), SCMP_SYS(open), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) < 0)
+		goto out;
+
+
+	/* special restrictions for openat, prevent opening files for writing */
+	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(openat), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY | O_RDWR, 0)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ERRNO (EACCES), SCMP_SYS(openat), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) < 0)
+		goto out;
+
+	if (seccomp_rule_add (ctx, SCMP_ACT_ERRNO (EACCES), SCMP_SYS(openat), 1,
+	                      SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) < 0)
+		goto out;
+
+	
+
+
+
+    // ------------ experimental filters ---------------
+
+
+
+
+    /* this filter is susceptible to TOCTOU race conditions, providing limited use */
+    /* allow opening only specified files identified by their file descriptors*/
+
+    // this requires either a list of all files to open (A LOT!!!)
+    // or needs to be applied only after initialisation, right before parsing
+    // if(seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(read), 1,
+    //                         SCMP_CMP(SCMP_CMP_EQ, fd)) < 0) // or < 1 ???
+    //     goto out;
+
+
+    /* restricting write access */
+
+    /* allow stdin */
+    // if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
+    //                         SCMP_CMP(0, SCMP_CMP_EQ, 0)) < 0 )
+    //     goto out;
+
+    /* allow stdout */
+    // if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
+    //                             SCMP_CMP(0, SCMP_CMP_EQ, 1)) < 0 )
+    //     goto out;
+
+    /* allow stderr */
+    if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
+                                 SCMP_CMP(0, SCMP_CMP_EQ, 2)) < 0 )
+        goto out;
+
+
+    /* restrict writev (write a vector) access */
+    // this does not seem reliable but it surprisingly is. investigate more
+    //if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(writev), 1,
+    //                            SCMP_CMP(0, SCMP_CMP_EQ, 3)) < 0 )
+    //    goto out;
+
+    //test if repeating this after some time or denying it works
+
+
+    // firest attempt to filter poll requests
+    // if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(poll), 1,
+    // 	                      SCMP_CMP(0, SCMP_CMP_MASKED_EQ, POLLIN | POLL, 0)) < 0)
+    // 	goto out;
+
+
+    /* restrict fcntl calls */
+    // this syscall sets the file descriptor to read write
+    //if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fcntl), 1,
+    //                            SCMP_CMP(0, SCMP_CMP_EQ, 3)) < 0 )
+    //    goto out;
+    // fcntl(3, F_GETFL)                       = 0x2 (flags O_RDWR)
+    // fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
+    // fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
+
+
+
+
+    // ------------------ end of experimental filters ------------------
+
+    //applying filter...
+    if (seccomp_load (ctx) >= 0){
+	// free ctx after the filter has been loaded into the kernel
+	seccomp_release(ctx);
+        return 0;
+    }
+
+ out:
+    //something went wrong
+    seccomp_release(ctx);
+    return 1;
+}
+
+
+#else /* HAVE_LIBSECCOMP */
+
+
+int protectedMode(void){
+
+    perror("No seccomp support compiled-in\n");
+    return 1;
+}
+
+int protectedView(void){
+
+    perror("No seccomp support compiled-in\n");
+    return 1;
+}
+
+int renderFilter(void){
+
+    perror("No seccomp support compiled-in\n");
+    return 1;
+}
+
+#endif /* HAVE_LIBSECCOMP */
diff -Naur mupdf-1.11-source/platform/x11/libsec.h mupdf/platform/x11/libsec.h
--- mupdf-1.11-source/platform/x11/libsec.h	1970-01-01 01:00:00.000000000 +0100
+++ mupdf/platform/x11/libsec.h	2017-03-15 23:01:14.285040855 +0100
@@ -0,0 +1,19 @@
+#ifndef SECCOMP_H
+#define SECCOMP_H
+
+/* basic filter */
+// this mode allows normal use
+// only dangerous syscalls are blacklisted
+int protectedMode(void);
+
+/* secure read-only mode */
+// whitelist minimal syscalls only
+// this mode does not allow writing files
+// or to open external links and applications
+// network connections are prohibited as well
+int protectedView(void);
+
+// restrict the process to use only the minimal syscalls needed to render the target document
+int renderFilter(void);
+
+#endif
diff -Naur mupdf-1.11-source/platform/x11/x11_main.c mupdf/platform/x11/x11_main.c
--- mupdf-1.11-source/platform/x11/x11_main.c	2017-04-05 13:02:21.000000000 +0200
+++ mupdf/platform/x11/x11_main.c	2017-08-20 13:54:43.330771684 +0200
@@ -1,5 +1,18 @@
 #include "pdfapp.h"
 
+//todo: set this flag in makefile
+#define HAVE_LIBSECCOMP
+#define USE_PROTECTEDVIEW
+#ifdef USE_PROTECTEDVIEW
+#ifndef HAVE_LIBSECCOMP
+#define HAVE_LIBSECCOMP
+#endif /* HAVE_LIBSECCOMP */
+#endif /* USE_PROTECTEDVIEW */
+
+#ifdef HAVE_LIBSECCOMP
+#include "libsec.h"
+#endif /* HAVE_LIBSECCOMP */
+
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #include <X11/Xatom.h>
@@ -108,6 +121,8 @@
 static struct timeval tmo_advance;
 static struct timeval tmo_at;
 
+int protectedViewSet = 0;
+
 /*
  * Dialog boxes
  */
@@ -723,32 +738,41 @@
 
 void winopenuri(pdfapp_t *app, char *buf)
 {
-	char *browser = getenv("BROWSER");
-	pid_t pid;
-	if (!browser)
-	{
+
+
+        //protectedView does not allow opening external apps
+        if(!protectedViewSet){
+
+
+	    char *browser = getenv("BROWSER");
+	    pid_t pid;
+	    if (!browser)
+		{
 #ifdef __APPLE__
-		browser = "open";
+		    browser = "open";
 #else
-		browser = "xdg-open";
+		    browser = "xdg-open";
 #endif
-	}
-	/* Fork once to start a child process that we wait on. This
-	 * child process forks again and immediately exits. The
-	 * grandchild process continues in the background. The purpose
-	 * of this strange two-step is to avoid zombie processes. See
-	 * bug 695701 for an explanation. */
-	pid = fork();
-	if (pid == 0)
-	{
-		if (fork() == 0)
+		}
+	    /* Fork once to start a child process that we wait on. This
+	     * child process forks again and immediately exits. The
+	     * grandchild process continues in the background. The purpose
+	     * of this strange two-step is to avoid zombie processes. See
+	     * bug 695701 for an explanation. */
+	    pid = fork();
+	    if (pid == 0)
 		{
-			execlp(browser, browser, buf, (char*)0);
-			fprintf(stderr, "cannot exec '%s'\n", browser);
+		    if (fork() == 0)
+			{
+			    execlp(browser, browser, buf, (char*)0);
+			    fprintf(stderr, "cannot exec '%s'\n", browser);
+			}
+		    exit(0);
 		}
-		exit(0);
-	}
-	waitpid(pid, NULL, 0);
+	    waitpid(pid, NULL, 0);
+
+	}//protectedViewSet
+	
 }
 
 static void onkey(int c, int modifiers)
@@ -816,12 +840,42 @@
 	fprintf(stderr, "\t-S -\tfont size for EPUB layout\n");
 	fprintf(stderr, "\t-U -\tuser style sheet for EPUB layout\n");
 	fprintf(stderr, "\t-X\tdisable document styles for EPUB layout\n");
+
+#ifdef HAVE_LIBSECCOMP
+#ifndef USE_PROTECTEDVIEW //this flag enforces protectedView by default
+
+	fprintf(stderr, "\t-s -\t[strict] - use protectedView (strict sandbox)\n");
+
+#endif /* USE_PROTECTEDVIEW */
+#endif /* HAVE_LIBSECCOMP */
+
 	exit(1);
 }
 
 int main(int argc, char **argv)
 {
-	int c;
+
+
+#ifdef HAVE_LIBSECCOMP
+
+    if(protectedMode()){
+        perror("SECCOMP initialisation failed");
+        exit(EXIT_FAILURE);
+    }
+
+#endif /* HAVE_LIBSECCOMP */
+
+#ifdef USE_PROTECTEDVIEW
+
+    if(protectedView()){
+        perror("SECCOMP initialisation failed");
+        exit(EXIT_FAILURE);
+    }
+
+#endif /* USE_PROTECTEDVIEW */
+    
+
+        int c;
 	int len;
 	char buf[128];
 	KeySym keysym;
@@ -847,7 +901,7 @@
 
 	pdfapp_init(ctx, &gapp);
 
-	while ((c = fz_getopt(argc, argv, "Ip:r:A:C:W:H:S:U:Xb:")) != -1)
+	while ((c = fz_getopt(argc, argv, "Ip:r:A:C:W:H:S:U:Xb:s:")) != -1)
 	{
 		switch (c)
 		{
@@ -868,6 +922,24 @@
 		case 'U': gapp.layout_css = fz_optarg; break;
 		case 'X': gapp.layout_use_doc_css = 0; break;
 		case 'b': bps = (fz_optarg && *fz_optarg) ? fz_atoi(fz_optarg) : 4096; break;
+
+#ifdef HAVE_LIBSECCOMP
+#ifndef USE_PROTECTEDVIEW //this flag enforces protectedView by default
+
+		case 's':
+			//activate protectedView Sandbox
+			protectedViewSet = 1;
+
+    			if(protectedView()){
+		            perror("SECCOMP initialisation failed");
+		            exit(EXIT_FAILURE);
+		    	}
+
+			break;
+			
+#endif /* USE_PROTECTEDVIEW */
+#endif /* HAVE_LIBSECCOMP */
+
 		default: usage();
 		}
 	}
@@ -882,6 +954,20 @@
 
 	winopen();
 
+	// at this stage, the socket connection to the X11 server has been established and further use of socket syscalls calls can blocked
+	// this filter allow only very few syscalls that are needed for rendering the target document
+	
+	#ifdef USE_PROTECTEDVIEW
+
+	if(renderFilter()){
+	  perror("SECCOMP initialisation failed");
+	  exit(EXIT_FAILURE);
+	  }
+	    
+	#endif /* USE_PROTECTEDVIEW */
+
+
+	
 	if (resolution == -1)
 		resolution = winresolution();
 	if (resolution < MINRES)