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Re: [PATCH v2 051/109] virtiofsd: add seccomp whitelist

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v2 051/109] virtiofsd: add seccomp whitelist
Date: Tue, 21 Jan 2020 16:54:41 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 
On 1/21/20 1:23 PM, Dr. David Alan Gilbert (git) wrote:

From: Stefan Hajnoczi <address@hidden>

Only allow system calls that are needed by virtiofsd.  All other system
calls cause SIGSYS to be directed at the thread and the process will
coredump.

Restricting system calls reduces the kernel attack surface and limits
what the process can do when compromised.

Signed-off-by: Stefan Hajnoczi <address@hidden>
with additional entries by:
Signed-off-by: Ganesh Maharaj Mahalingam <address@hidden>
Signed-off-by: Masayoshi Mizuma <address@hidden>
Signed-off-by: Misono Tomohiro <address@hidden>
Signed-off-by: piaojun <address@hidden>
Signed-off-by: Vivek Goyal <address@hidden>
Signed-off-by: Eric Ren <address@hidden>
Signed-off-by: Dr. David Alan Gilbert <address@hidden>
---
  Makefile                         |   2 +-
  tools/virtiofsd/Makefile.objs    |   5 +-
  tools/virtiofsd/passthrough_ll.c |   2 +
  tools/virtiofsd/seccomp.c        | 150 +++++++++++++++++++++++++++++++
  tools/virtiofsd/seccomp.h        |  14 +++
  5 files changed, 171 insertions(+), 2 deletions(-)
  create mode 100644 tools/virtiofsd/seccomp.c
  create mode 100644 tools/virtiofsd/seccomp.h

diff --git a/Makefile b/Makefile
index a87e06ad93..967d59c98a 100644
--- a/Makefile
+++ b/Makefile
@@ -327,7 +327,7 @@ HELPERS-y += vhost-user-gpu$(EXESUF)
  vhost-user-json-y += contrib/vhost-user-gpu/50-qemu-gpu.json
  endif
-ifdef CONFIG_LINUX 
+ifeq ($(CONFIG_LINUX)$(CONFIG_SECCOMP),yy)
  HELPERS-y += virtiofsd$(EXESUF)


Something is weird here, because I got:

$ make virtiofsd
  ...
  CC      tools/virtiofsd/seccomp.o
tools/virtiofsd/seccomp.c:14:21: fatal error: seccomp.h: No such file or directory 
 #include <seccomp.h>
                     ^

Indeed I don't have libseccomp installed, ./configure reported:

...
QGA MSI support   no
seccomp support   no
coroutine backend ucontext
coroutine pool    yes
debug stack usage no
...

Note also:

$ make print-CONFIG_LINUX
CONFIG_LINUX=y
$ make print-CONFIG_SECCOMP
CONFIG_SECCOMP=
$ make print-CONFIG_LIBCAP_NG
CONFIG_LIBCAP_NG=y
$ make print-HELPERS-y
HELPERS-y=qemu-bridge-helper


  vhost-user-json-y += tools/virtiofsd/50-qemu-virtiofsd.json
  endif
diff --git a/tools/virtiofsd/Makefile.objs b/tools/virtiofsd/Makefile.objs
index 45a807500d..076f667e46 100644
--- a/tools/virtiofsd/Makefile.objs
+++ b/tools/virtiofsd/Makefile.objs
@@ -5,5 +5,8 @@ virtiofsd-obj-y = buffer.o \
                    fuse_signals.o \
                    fuse_virtio.o \
                    helper.o \
-                  passthrough_ll.o
+                  passthrough_ll.o \
+                  seccomp.o
+seccomp.o-cflags := $(SECCOMP_CFLAGS) 
+seccomp.o-libs := $(SECCOMP_LIBS)
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 752beb459a..8748e64f33 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -58,6 +58,7 @@
  #include <unistd.h>
#include "passthrough_helpers.h" 
+#include "seccomp.h"
struct lo_map_elem { 
      union {
@@ -2090,6 +2091,7 @@ static void setup_sandbox(struct lo_data *lo, struct 
fuse_session *se)
  {
      setup_namespaces(lo, se);
      setup_mounts(lo->source);
+    setup_seccomp();
  }
int main(int argc, char *argv[]) 
diff --git a/tools/virtiofsd/seccomp.c b/tools/virtiofsd/seccomp.c
new file mode 100644
index 0000000000..2aa4d3cc66
--- /dev/null
+++ b/tools/virtiofsd/seccomp.c
@@ -0,0 +1,150 @@
+/*
+ * Seccomp sandboxing for virtiofsd
+ *
+ * Copyright (C) 2019 Red Hat, Inc.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "seccomp.h"
+#include "fuse_i.h"
+#include "fuse_log.h"
+#include <errno.h>
+#include <glib.h>
+#include <seccomp.h>
+#include <stdlib.h>
+
+/* Bodge for libseccomp 2.4.2 which broke ppoll */
+#if !defined(__SNR_ppoll) && defined(__SNR_brk)
+#ifdef __NR_ppoll
+#define __SNR_ppoll __NR_ppoll
+#else
+#define __SNR_ppoll __PNR_ppoll
+#endif
+#endif
+
+static const int syscall_whitelist[] = {
+    /* TODO ireg sem*() syscalls */
+    SCMP_SYS(brk),
+    SCMP_SYS(capget), /* For CAP_FSETID */
+    SCMP_SYS(capset),
+    SCMP_SYS(clock_gettime),
+    SCMP_SYS(clone),
+#ifdef __NR_clone3
+    SCMP_SYS(clone3),
+#endif
+    SCMP_SYS(close),
+    SCMP_SYS(copy_file_range),
+    SCMP_SYS(dup),
+    SCMP_SYS(eventfd2),
+    SCMP_SYS(exit),
+    SCMP_SYS(exit_group),
+    SCMP_SYS(fallocate),
+    SCMP_SYS(fchmodat),
+    SCMP_SYS(fchownat),
+    SCMP_SYS(fcntl),
+    SCMP_SYS(fdatasync),
+    SCMP_SYS(fgetxattr),
+    SCMP_SYS(flistxattr),
+    SCMP_SYS(flock),
+    SCMP_SYS(fremovexattr),
+    SCMP_SYS(fsetxattr),
+    SCMP_SYS(fstat),
+    SCMP_SYS(fstatfs),
+    SCMP_SYS(fsync),
+    SCMP_SYS(ftruncate),
+    SCMP_SYS(futex),
+    SCMP_SYS(getdents),
+    SCMP_SYS(getdents64),
+    SCMP_SYS(getegid),
+    SCMP_SYS(geteuid),
+    SCMP_SYS(getpid),
+    SCMP_SYS(gettid),
+    SCMP_SYS(gettimeofday),
+    SCMP_SYS(linkat),
+    SCMP_SYS(lseek),
+    SCMP_SYS(madvise),
+    SCMP_SYS(mkdirat),
+    SCMP_SYS(mknodat),
+    SCMP_SYS(mmap),
+    SCMP_SYS(mprotect),
+    SCMP_SYS(mremap),
+    SCMP_SYS(munmap),
+    SCMP_SYS(newfstatat),
+    SCMP_SYS(open),
+    SCMP_SYS(openat),
+    SCMP_SYS(ppoll),
+    SCMP_SYS(prctl), /* TODO restrict to just PR_SET_NAME? */
+    SCMP_SYS(preadv),
+    SCMP_SYS(pread64),
+    SCMP_SYS(pwritev),
+    SCMP_SYS(pwrite64),
+    SCMP_SYS(read),
+    SCMP_SYS(readlinkat),
+    SCMP_SYS(recvmsg),
+    SCMP_SYS(renameat),
+    SCMP_SYS(renameat2),
+    SCMP_SYS(rt_sigaction),
+    SCMP_SYS(rt_sigprocmask),
+    SCMP_SYS(rt_sigreturn),
+    SCMP_SYS(sendmsg),
+    SCMP_SYS(setresgid),
+    SCMP_SYS(setresuid),
+#ifdef __NR_setresgid32
+    SCMP_SYS(setresgid32),
+#endif
+#ifdef __NR_setresuid32
+    SCMP_SYS(setresuid32),
+#endif
+    SCMP_SYS(set_robust_list),
+    SCMP_SYS(symlinkat),
+    SCMP_SYS(time), /* Rarely needed, except on static builds */
+    SCMP_SYS(tgkill),
+    SCMP_SYS(unlinkat),
+    SCMP_SYS(utimensat),
+    SCMP_SYS(write),
+    SCMP_SYS(writev),
+};
+
+void setup_seccomp(void)
+{
+    scmp_filter_ctx ctx;
+    size_t i;
+
+#ifdef SCMP_ACT_KILL_PROCESS
+    ctx = seccomp_init(SCMP_ACT_KILL_PROCESS);
+    /* Handle a newer libseccomp but an older kernel */
+    if (!ctx && errno == EOPNOTSUPP) {
+        ctx = seccomp_init(SCMP_ACT_TRAP);
+    }
+#else
+    ctx = seccomp_init(SCMP_ACT_TRAP);
+#endif
+    if (!ctx) {
+        fuse_log(FUSE_LOG_ERR, "seccomp_init() failed\n");
+        exit(1);
+    }
+
+    for (i = 0; i < G_N_ELEMENTS(syscall_whitelist); i++) {
+        if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW,
+                             syscall_whitelist[i], 0) != 0) {
+            fuse_log(FUSE_LOG_ERR, "seccomp_rule_add syscall %d",
+                     syscall_whitelist[i]);
+            exit(1);
+        }
+    }
+
+    /* libvhost-user calls this for post-copy migration, we don't need it */
+    if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(ENOSYS),
+                         SCMP_SYS(userfaultfd), 0) != 0) {
+        fuse_log(FUSE_LOG_ERR, "seccomp_rule_add userfaultfd failed\n");
+        exit(1);
+    }
+
+    if (seccomp_load(ctx) < 0) {
+        fuse_log(FUSE_LOG_ERR, "seccomp_load() failed\n");
+        exit(1);
+    }
+
+    seccomp_release(ctx);
+}
diff --git a/tools/virtiofsd/seccomp.h b/tools/virtiofsd/seccomp.h
new file mode 100644
index 0000000000..86bce72652
--- /dev/null
+++ b/tools/virtiofsd/seccomp.h
@@ -0,0 +1,14 @@
+/*
+ * Seccomp sandboxing for virtiofsd
+ *
+ * Copyright (C) 2019 Red Hat, Inc.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef VIRTIOFSD_SECCOMP_H
+#define VIRTIOFSD_SECCOMP_H
+
+void setup_seccomp(void);
+
+#endif /* VIRTIOFSD_SECCOMP_H */
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