Re: [Qemu-devel] [PATCH 3/4] Support for "double whitelist" filters

[Blue Swirl]

On Wed, Oct 17, 2012 at 1:15 PM, Eduardo Otubo <address@hidden> wrote:
> This patch includes a second whitelist right before the main loop. It's
> a smaller and more restricted whitelist, excluding execve() among many
> others.
>
> Signed-off-by: Eduardo Otubo <address@hidden>
> ---
>  qemu-seccomp.c | 94 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++------
>  qemu-seccomp.h |  7 ++++-
>  vl.c           | 13 +++++++-
>  3 files changed, 103 insertions(+), 11 deletions(-)
>
> diff --git a/qemu-seccomp.c b/qemu-seccomp.c
> index a25f2fa..9c68af5 100644
> --- a/qemu-seccomp.c
> +++ b/qemu-seccomp.c
> @@ -13,6 +13,7 @@
>   * GNU GPL, version 2 or (at your option) any later version.
>   */
>  #include <stdio.h>
> +#include <stdlib.h>
>  #include <seccomp.h>
>  #include "qemu-seccomp.h"
>
> @@ -21,7 +22,7 @@ struct QemuSeccompSyscall {
>      uint8_t priority;
>  };
>
> -static const struct QemuSeccompSyscall seccomp_whitelist[] = {
> +static const struct QemuSeccompSyscall seccomp_whitelist_init[] = {
>      { SCMP_SYS(timer_settime), 255 },
>      { SCMP_SYS(timer_gettime), 254 },
>      { SCMP_SYS(futex), 253 },
> @@ -118,27 +119,102 @@ static const struct QemuSeccompSyscall 
> seccomp_whitelist[] = {
>      { SCMP_SYS(accept4), 242 }
>  };
>
> -int seccomp_start(void)
> +static const struct QemuSeccompSyscall seccomp_whitelist_main_loop[] = {
> +    { SCMP_SYS(timer_settime), 255 },
> +    { SCMP_SYS(timer_gettime), 254 },
> +    { SCMP_SYS(futex), 253 },
> +    { SCMP_SYS(select), 252 },
> +    { SCMP_SYS(recvfrom), 251 },
> +    { SCMP_SYS(sendto), 250 },
> +    { SCMP_SYS(read), 249 },
> +    { SCMP_SYS(brk), 248 },
> +    { SCMP_SYS(mmap), 247 },
> +#if defined(__i386__)
> +    { SCMP_SYS(fcntl64), 245 },
> +    { SCMP_SYS(fstat64), 245 },
> +    { SCMP_SYS(stat64), 245 },
> +    { SCMP_SYS(getgid32), 245 },
> +    { SCMP_SYS(getegid32), 245 },
> +    { SCMP_SYS(getuid32), 245 },
> +    { SCMP_SYS(geteuid32), 245 },
> +    { SCMP_SYS(sigreturn), 245 },
> +    { SCMP_SYS(_newselect), 245 },
> +    { SCMP_SYS(_llseek), 245 },
> +    { SCMP_SYS(mmap2), 245},
> +    { SCMP_SYS(sigprocmask), 245 },
> +#endif
> +    { SCMP_SYS(exit), 245 },
> +    { SCMP_SYS(timer_delete), 245 },
> +    { SCMP_SYS(exit_group), 245 },
> +    { SCMP_SYS(rt_sigreturn), 245 },
> +    { SCMP_SYS(madvise), 245 },
> +    { SCMP_SYS(write), 244 },
> +    { SCMP_SYS(fcntl), 243 },
> +    { SCMP_SYS(tgkill), 242 },
> +    { SCMP_SYS(rt_sigaction), 242 },
> +    { SCMP_SYS(pipe2), 242 },
> +    { SCMP_SYS(munmap), 242 },
> +    { SCMP_SYS(mremap), 242 },
> +    { SCMP_SYS(getsockname), 242 },
> +    { SCMP_SYS(getpeername), 242 },
> +    { SCMP_SYS(close), 242 },
> +    { SCMP_SYS(accept4), 242 }

It's nice to see that for example open, creat, unlink, socket, bind,
mprotect, setrlimit and kill are not present.

> +};
> +
> +static int
> +process_whitelist(const struct QemuSeccompSyscall *whitelist,
> +                  unsigned int size, scmp_filter_ctx *ctx)
>  {
>      int rc = 0;
> +
>      unsigned int i = 0;
> -    scmp_filter_ctx ctx;
> +
> +    for (i = 0; i < size; i++) {
> +        rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, whitelist[i].num, 0);
> +        if (rc < 0) {
> +            return -1;
> +        }
> +
> +        rc = seccomp_syscall_priority(ctx, whitelist[i].num,
> +                                      whitelist[i].priority);
> +        if (rc < 0) {
> +            return -1;
> +        }
> +    }
> +    return 0;
> +}
> +
> +int
> +seccomp_start(enum whitelist_mode mode, scmp_filter_ctx *ctx)
> +{
> +    int rc = 0;
>
>      ctx = seccomp_init(SCMP_ACT_KILL);
>      if (ctx == NULL) {
> +        rc = -1;
>          goto seccomp_return;
>      }
>
> -    for (i = 0; i < ARRAY_SIZE(seccomp_whitelist); i++) {
> -        rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, seccomp_whitelist[i].num, 
> 0);
> -        if (rc < 0) {
> +    switch (mode) {
> +    case INIT:
> +        if (process_whitelist
> +            (seccomp_whitelist_init,
> +             ARRAY_SIZE(seccomp_whitelist_init), ctx) < 0) {
> +            rc = -1;
>              goto seccomp_return;
>          }
> -        rc = seccomp_syscall_priority(ctx, seccomp_whitelist[i].num,
> -                                      seccomp_whitelist[i].priority);
> -        if (rc < 0) {
> +        break;
> +    case MAIN_LOOP:
> +        if (process_whitelist
> +            (seccomp_whitelist_main_loop,
> +             ARRAY_SIZE(seccomp_whitelist_main_loop), ctx) < 0) {
> +            rc = -1;
>              goto seccomp_return;
>          }
> +        break;
> +    default:
> +        rc = -1;
> +        goto seccomp_return;
>      }
>
>      rc = seccomp_load(ctx);
> diff --git a/qemu-seccomp.h b/qemu-seccomp.h
> index b2fc3f8..1c97978 100644
> --- a/qemu-seccomp.h
> +++ b/qemu-seccomp.h
> @@ -18,5 +18,10 @@
>  #include <seccomp.h>
>  #include "osdep.h"
>
> -int seccomp_start(void);
> +enum whitelist_mode {
> +    INIT = 0,
> +    MAIN_LOOP = 1,
> +};
> +
> +int seccomp_start(enum whitelist_mode mode, scmp_filter_ctx *ctx);
>  #endif
> diff --git a/vl.c b/vl.c
> index bec68cd..773d488 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -278,6 +278,7 @@ static int default_vga = 1;
>
>  #ifdef CONFIG_SECCOMP
>  bool seccomp_on = true;
> +scmp_filter_ctx ctx;

This should be a local variable to main(), maybe also named
'main_loop_ctx' so we can add further contexts.

>  #endif
>
>  static struct {
> @@ -777,7 +778,7 @@ static int bt_parse(const char *opt)
>  static int install_seccomp_filters(void)
>  {
>  #ifdef CONFIG_SECCOMP
> -    if (seccomp_start() < 0) {
> +    if (seccomp_start(INIT, &ctx) < 0) {
>          qerror_report(ERROR_CLASS_GENERIC_ERROR,
>                  "failed to install seccomp syscall filter in the kernel");
>          return -1;
> @@ -3794,6 +3795,16 @@ int main(int argc, char **argv, char **envp)
>
>      os_setup_post();
>
> +    if (seccomp_on) {

'seccomp_on' is only available with CONFIG_SECCOMP, so this would break build.

> +#ifdef CONFIG_SECCOMP
> +        if (seccomp_start(MAIN_LOOP, &ctx) < 0) {
> +            qerror_report(ERROR_CLASS_GENERIC_ERROR,
> +                          "failed to install seccomp syscall filter in the 
> kernel");

This error message could be different from the first one.

> +            return -1;
> +        }
> +#endif
> +    }
> +
>      resume_all_vcpus();
>      main_loop();
>      bdrv_close_all();
> --
> 1.7.12
>
>