From: Christos Zoulas <christos@zoulas.com>
Date: Sun, 24 Sep 2017 16:04:55 +0000 (+0000)
Subject: Add and enable libseccomp support (Paul Moore)
X-Git-Tag: FILE5_33~96
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=3ddad464137378f3b57b27d5df6409185b6b8de7;p=file
Add and enable libseccomp support (Paul Moore)
---
diff --git a/ChangeLog b/ChangeLog
index 2063a23b..f76093c1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2017-09-24 12:02 Christos Zoulas <christos@zoulas.com>
+
+ * seccomp support (Paul Moore)
+
2017-09-02 11:53 Christos Zoulas <christos@zoulas.com>
* release 5.32
diff --git a/configure.ac b/configure.ac
index 946198be..fee4eded 100644
--- a/configure.ac
+++ b/configure.ac
@@ -39,6 +39,11 @@ AC_ARG_ENABLE(zlib,
[AS_HELP_STRING([--disable-zlib], [disable zlib compression support @<:@default=auto@:>@])])
AC_MSG_RESULT($enable_zlib)
+AC_MSG_CHECKING(for libseccomp support)
+AC_ARG_ENABLE(libseccomp,
+[AS_HELP_STRING([--disable-libseccomp], [disable libseccomp sandboxing @<:@default=auto@:>@])])
+AC_MSG_RESULT($enable_libseccomp)
+
AC_MSG_CHECKING(for file formats in man section 5)
AC_ARG_ENABLE(fsect-man5,
[ --enable-fsect-man5 enable file formats in man section 5],
@@ -158,6 +163,9 @@ dnl Checks for libraries
if test "$enable_zlib" != "no"; then
AC_CHECK_LIB(z, gzopen)
fi
+if test "$enable_libseccomp" != "no"; then
+ AC_CHECK_LIB(seccomp, seccomp_init)
+fi
if test "$MINGW" = 1; then
AC_CHECK_LIB(gnurx,regexec,,AC_MSG_ERROR([libgnurx is required to build file(1) with MinGW]))
fi
diff --git a/src/Makefile.am b/src/Makefile.am
index 155aec44..cbdccac2 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -19,7 +19,7 @@ MINGWLIBS =
endif
libmagic_la_LIBADD = $(LTLIBOBJS) $(MINGWLIBS)
-file_SOURCES = file.c
+file_SOURCES = file.c seccomp.c
file_LDADD = libmagic.la
CLEANFILES = magic.h
EXTRA_DIST = magic.h.in
diff --git a/src/file.c b/src/file.c
index 90e0b7e7..5152f423 100644
--- a/src/file.c
+++ b/src/file.c
@@ -32,7 +32,7 @@
#include "file.h"
#ifndef lint
-FILE_RCSID("@(#)$File: file.c,v 1.173 2017/09/18 20:40:10 christos Exp $")
+FILE_RCSID("@(#)$File: file.c,v 1.174 2017/09/24 16:04:56 christos Exp $")
#endif /* lint */
#include "magic.h"
@@ -186,6 +186,15 @@ main(int argc, char *argv[])
file_setprogname(progname);
+#ifdef HAVE_LIBSECCOMP
+#if 0
+ if (enable_sandbox_basic() == -1)
+#else
+ if (enable_sandbox_full() == -1)
+#endif
+ file_err(EXIT_FAILURE, "SECCOMP initialisation failed");
+#endif /* HAVE_LIBSECCOMP */
+
#ifdef S_IFLNK
posixly = getenv("POSIXLY_CORRECT") != NULL;
flags |= posixly ? MAGIC_SYMLINK : 0;
diff --git a/src/file.h b/src/file.h
index 3a993a3e..79490508 100644
--- a/src/file.h
+++ b/src/file.h
@@ -27,7 +27,7 @@
*/
/*
* file.h - definitions for file(1) program
- * @(#)$File: file.h,v 1.184 2017/09/18 20:40:10 christos Exp $
+ * @(#)$File: file.h,v 1.185 2017/09/24 16:04:56 christos Exp $
*/
#ifndef __file_h__
@@ -590,6 +590,18 @@ const char *fmtcheck(const char *, const char *)
__attribute__((__format_arg__(2)));
#endif
+#ifdef HAVE_LIBSECCOMP
+// basic filter
+// this mode should not interfere with normal operations
+// only some dangerous syscalls are blacklisted
+int enable_sandbox_basic(void);
+
+// enhanced filter
+// this mode allows only the necessary syscalls used during normal operation
+// extensive testing required !!!
+int enable_sandbox_full(void);
+#endif
+
protected const char *file_getprogname(void);
protected void file_setprogname(const char *);
protected void file_err(int, const char *, ...)
diff --git a/src/seccomp.c b/src/seccomp.c
new file mode 100644
index 00000000..88c73810
--- /dev/null
+++ b/src/seccomp.c
@@ -0,0 +1,246 @@
+/*
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice immediately at the beginning of the file, without modification,
+ * this list of conditions, and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+/*
+ * libseccomp hooks.
+ */
+#include "file.h"
+
+#ifndef lint
+FILE_RCSID("@(#)$File: seccomp.c,v 1.1 2017/09/24 16:04:56 christos Exp $")
+#endif /* lint */
+
+#if 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) \
+ do \
+ if (seccomp_rule_add (ctx, SCMP_ACT_KILL, SCMP_SYS(call), 0) == -1) \
+ goto out; \
+ while (/*CONSTCOND*/0)
+#define ALLOW_RULE(call) \
+ do \
+ if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(call), 0) == -1) \
+ goto out; \
+ while (/*CONSTCOND*/0)
+
+static scmp_filter_ctx ctx;
+
+
+int
+enable_sandbox_basic(void)
+{
+
+ if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
+ return -1;
+
+#if 0
+ // prevent escape via ptrace
+ prctl(PR_SET_DUMPABLE, 0);
+#endif
+
+ if (prctl (PR_SET_DUMPABLE, 0, 0, 0, 0) == -1)
+ return -1;
+
+ // 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);
+#ifdef __NR_kexec_file_load
+ DENY_RULE(kexec_file_load);
+#endif
+ 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);
+
+ // blocking dangerous syscalls that file should not need
+ DENY_RULE (execve);
+ DENY_RULE (socket);
+ // ...
+
+
+ // applying filter...
+ if (seccomp_load (ctx) == -1)
+ goto out;
+ // free ctx after the filter has been loaded into the kernel
+ seccomp_release(ctx);
+ return 0;
+
+out:
+ seccomp_release(ctx);
+ return -1;
+}
+
+
+int
+enable_sandbox_full(void)
+{
+
+ // prevent child processes from getting more priv e.g. via setuid,
+ // capabilities, ...
+ if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
+ return -1;
+
+ if (prctl(PR_SET_DUMPABLE, 0, 0, 0, 0) == -1)
+ return -1;
+
+ // initialize the filter
+ ctx = seccomp_init(SCMP_ACT_KILL);
+ if (ctx == NULL)
+ return -1;
+
+ ALLOW_RULE(access);
+ ALLOW_RULE(brk);
+ ALLOW_RULE(close);
+ ALLOW_RULE(dup2);
+ ALLOW_RULE(exit);
+ ALLOW_RULE(exit_group);
+ ALLOW_RULE(fcntl);
+ ALLOW_RULE(fstat);
+ ALLOW_RULE(getdents);
+ ALLOW_RULE(ioctl);
+ ALLOW_RULE(lseek);
+ ALLOW_RULE(lstat);
+ ALLOW_RULE(mmap);
+ ALLOW_RULE(mprotect);
+ ALLOW_RULE(mremap);
+ ALLOW_RULE(munmap);
+ ALLOW_RULE(open);
+ ALLOW_RULE(openat);
+ ALLOW_RULE(pread64);
+ ALLOW_RULE(read);
+ ALLOW_RULE(rt_sigaction);
+ ALLOW_RULE(rt_sigprocmask);
+ ALLOW_RULE(rt_sigreturn);
+ ALLOW_RULE(select);
+ ALLOW_RULE(stat);
+ ALLOW_RULE(sysinfo);
+ ALLOW_RULE(unlink);
+ ALLOW_RULE(write);
+
+
+#if 0
+ // needed by valgrind
+ ALLOW_RULE(gettid);
+ ALLOW_RULE(getpid);
+ ALLOW_RULE(readlink);
+ ALLOW_RULE(rt_sigtimedwait);
+#endif
+
+#if 0
+ /* 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)) == -1)
+ goto out;
+
+ if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
+ SCMP_CMP(0, SCMP_CMP_EQ, AF_LOCAL)) == -1)
+ 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)) == -1)
+ 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)) == -1)
+ 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)) == -1)
+ goto out;
+
+
+ /* allow stderr */
+ if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
+ SCMP_CMP(0, SCMP_CMP_EQ, 2)) == -1)
+ goto out;
+#endif
+
+ // applying filter...
+ if (seccomp_load(ctx) == -1)
+ goto out;
+ // 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;
+}
+#endif