Allow any syscall to be blacklisted (#1447)

Allow any syscall to be blacklisted with aid of LD_PRELOAD library,
libpostexecseccomp.so.

Closes: #1447

3 files changed, 110 insertions, 0 deletions

diff --git a/src/libpostexecseccomp/Makefile.in b/src/libpostexecseccomp/Makefile.in
new file mode 100644
index 000000000..92803342c
--- /dev/null
+++ b/src/libpostexecseccomp/Makefile.in
@@ -0,0 +1,26 @@
+CC=@CC@
+PREFIX=@prefix@
+VERSION=@PACKAGE_VERSION@
+NAME=@PACKAGE_NAME@
+HAVE_FATAL_WARNINGS=@HAVE_FATAL_WARNINGS@
+
+H_FILE_LIST       = $(sort $(wildcard *.[h]))
+C_FILE_LIST       = $(sort $(wildcard *.c))
+OBJS = $(C_FILE_LIST:.c=.o)
+BINOBJS =  $(foreach file, $(OBJS), $file)
+CFLAGS += -ggdb $(HAVE_FATAL_WARNINGS) -O2 -DVERSION='"$(VERSION)"' -fstack-protector-all -D_FORTIFY_SOURCE=2 -fPIC -Wformat -Wformat-security
+LDFLAGS += -pie -Wl,-z,relro -Wl,-z,now
+
+all: libpostexecseccomp.so
+
+%.o : %.c $(H_FILE_LIST)
+        $(CC) $(CFLAGS) $(INCLUDE) -c $< -o $@
+
+libpostexecseccomp.so: $(OBJS)
+        $(CC) $(LDFLAGS) -shared -fPIC -z relro -o $@ $(OBJS) -ldl
+
+
+clean:; rm -f $(OBJS) libpostexecseccomp.so
+
+distclean: clean
+        rm -fr Makefile
diff --git a/src/libpostexecseccomp/libpostexecseccomp.c b/src/libpostexecseccomp/libpostexecseccomp.c
new file mode 100644
index 000000000..801f968a6
--- /dev/null
+++ b/src/libpostexecseccomp/libpostexecseccomp.c
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2017 Firejail Authors
+ *
+ * This file is part of firejail project
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+#include "libpostexecseccomp.h"
+#include <fcntl.h>
+#include <linux/audit.h>
+#include <linux/bpf.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h>
+#include <sys/mman.h>
+#include <sys/prctl.h>
+#include <sys/ptrace.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+__attribute__((constructor))
+static void load_seccomp(void) {
+        int fd = open(RUN_SECCOMP_POSTEXEC, O_RDONLY);
+        if (fd == -1)
+                return;
+
+        int size = lseek(fd, 0, SEEK_END);
+        unsigned short entries = (unsigned short) size / (unsigned short) sizeof(struct sock_filter);
+        struct sock_filter *filter = MAP_FAILED;
+        if (size != 0)
+                filter = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+
+        close(fd);
+
+        if (size == 0 || filter == MAP_FAILED)
+                return;
+
+        // install filter
+        struct sock_fprog prog = {
+                .len = entries,
+                .filter = filter,
+        };
+
+        prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+        prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
+        munmap(filter, size);
+}
diff --git a/src/libpostexecseccomp/libpostexecseccomp.h b/src/libpostexecseccomp/libpostexecseccomp.h
new file mode 100644
index 000000000..c4aca540a
--- /dev/null
+++ b/src/libpostexecseccomp/libpostexecseccomp.h
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2017 Firejail Authors
+ *
+ * This file is part of firejail project
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+#ifndef LIBPOSTEXECSECCOMP_H
+#define LIBPOSTEXECSECCOMP_H
+
+#define RUN_SECCOMP_POSTEXEC    "/run/firejail/mnt/seccomp.postexec"
+
+#endif