Re: [PATCH 050/104] virtiofsd: add seccomp whitelist

[Daniel P . Berrangé]

On Thu, Dec 12, 2019 at 04:38:10PM +0000, 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>
> ---
>  Makefile                         |   2 +
>  tools/virtiofsd/Makefile.objs    |   5 +-
>  tools/virtiofsd/passthrough_ll.c |   2 +
>  tools/virtiofsd/seccomp.c        | 141 +++++++++++++++++++++++++++++++
>  tools/virtiofsd/seccomp.h        |  14 +++
>  5 files changed, 163 insertions(+), 1 deletion(-)
>  create mode 100644 tools/virtiofsd/seccomp.c
>  create mode 100644 tools/virtiofsd/seccomp.h
> 
> diff --git a/Makefile b/Makefile
> index 8a5746d8a0..3f5d04e1f7 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -322,8 +322,10 @@ HELPERS-y =
>  HELPERS-$(call land,$(CONFIG_SOFTMMU),$(CONFIG_LINUX)) = 
> qemu-bridge-helper$(EXESUF)
>  
>  ifdef CONFIG_LINUX
> +ifdef CONFIG_SECCOMP
>  HELPERS-y += virtiofsd$(EXESUF)
>  vhost-user-json-y += tools/virtiofsd/50-qemu-virtiofsd.json
> +endif
>  
>  ifdef CONFIG_VIRGL
>  ifdef CONFIG_GBM
> diff --git a/tools/virtiofsd/Makefile.objs b/tools/virtiofsd/Makefile.objs
> index 67be16332c..941b19f18e 100644
> --- a/tools/virtiofsd/Makefile.objs
> +++ b/tools/virtiofsd/Makefile.objs
> @@ -6,5 +6,8 @@ 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 754ef2618b..701608c6df 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"
>  
>  #define HAVE_POSIX_FALLOCATE 1
>  struct lo_map_elem {
> @@ -2073,6 +2074,7 @@ 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..6359bb55bb
> --- /dev/null
> +++ b/tools/virtiofsd/seccomp.c
> @@ -0,0 +1,141 @@
> +/*
> + * 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),

clone2 ?  clone3 ? IIC some archs in Linux
will require the newer variants.

> +    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),

Should be setresgid32 instead I think. We don't
want the legacy syscall that's limted to 16-bit GIDs

Needs the code fix I mention in an earlier patch too.

> +    SCMP_SYS(setresuid),

Same as above

> +    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),
> +};


Regards,
Daniel
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