Re: [Qemu-devel] [PATCH 2/5] seccomp: add obsolete argument to command line

[Eduardo Otubo <eduardo.otubo@profitbricks.com>]

On Tue, Mar 14, 2017 at 01=01=11PM +0100, Thomas Huth wrote:
> On 14.03.2017 12:32, Eduardo Otubo wrote:
> > This patch introduces the argument [,obsolete=allow] to the `-sandbox on'
> > option. It allows Qemu to run safely on old system that still relies on
> > old system calls.
> > 
> > Signed-off-by: Eduardo Otubo <eduardo.otubo@profitbricks.com>
> > ---
> >  include/sysemu/seccomp.h |  4 +++-
> >  qemu-options.hx          |  9 +++++++--
> >  qemu-seccomp.c           | 47 ++++++++++++++++++++++++++++++++++++++++++++++-
> >  vl.c                     | 16 +++++++++++++++-
> >  4 files changed, 71 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/sysemu/seccomp.h b/include/sysemu/seccomp.h
> > index cfc06008cb..7a7bde246b 100644
> > --- a/include/sysemu/seccomp.h
> > +++ b/include/sysemu/seccomp.h
> > @@ -15,7 +15,9 @@
> >  #ifndef QEMU_SECCOMP_H
> >  #define QEMU_SECCOMP_H
> >  
> > +#define OBSOLETE    0x0001
> > +
> >  #include <seccomp.h>
> >  
> > -int seccomp_start(void);
> > +int seccomp_start(uint8_t seccomp_opts);
> >  #endif
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 8dd8ee34a6..1403d0c85f 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -3732,13 +3732,18 @@ Old param mode (ARM only).
> >  ETEXI
> >  
> >  DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \
> > -    "-sandbox <arg>  Enable seccomp mode 2 system call filter (default 'off').\n",
> > +    "-sandbox on[,obsolete=allow]  Enable seccomp mode 2 system call filter (default 'off').\n" \
> > +    "                              obsolete: Allow obsolete system calls",
> >      QEMU_ARCH_ALL)
> >  STEXI
> > -@item -sandbox @var{arg}
> > +@item -sandbox @var{arg}[,obsolete=@var{string}]
> >  @findex -sandbox
> >  Enable Seccomp mode 2 system call filter. 'on' will enable syscall filtering and 'off' will
> >  disable it.  The default is 'off'.
> > +@table @option
> > +@item obsolete=@var{string}
> > +Enable Obsolete system calls
> > +@end table
> >  ETEXI
> >  
> >  DEF("readconfig", HAS_ARG, QEMU_OPTION_readconfig,
> > diff --git a/qemu-seccomp.c b/qemu-seccomp.c
> > index f8877b07b5..5ef36890da 100644
> > --- a/qemu-seccomp.c
> > +++ b/qemu-seccomp.c
> > @@ -31,6 +31,35 @@ struct QemuSeccompSyscall {
> >      uint8_t priority;
> >  };
> >  
> > +static const struct QemuSeccompSyscall obsolete[] = {
> > +    { SCMP_SYS(readdir), 255 },
> > +    { SCMP_SYS(_sysctl), 255 },
> > +    { SCMP_SYS(afs_syscall), 255 },
> > +    { SCMP_SYS(bdflush), 255 },
> > +    { SCMP_SYS(break), 255 },
> > +    { SCMP_SYS(create_module), 255 },
> > +    { SCMP_SYS(ftime), 255 },
> > +    { SCMP_SYS(get_kernel_syms), 255 },
> > +    { SCMP_SYS(getpmsg), 255 },
> > +    { SCMP_SYS(gtty), 255 },
> > +    { SCMP_SYS(lock), 255 },
> > +    { SCMP_SYS(mpx), 255 },
> > +    { SCMP_SYS(prof), 255 },
> > +    { SCMP_SYS(profil), 255 },
> > +    { SCMP_SYS(putpmsg), 255 },
> > +    { SCMP_SYS(query_module), 255 },
> > +    { SCMP_SYS(security), 255 },
> > +    { SCMP_SYS(sgetmask), 255 },
> > +    { SCMP_SYS(ssetmask), 255 },
> > +    { SCMP_SYS(stty), 255 },
> > +    { SCMP_SYS(sysfs), 255 },
> > +    { SCMP_SYS(tuxcall), 255 },
> > +    { SCMP_SYS(ulimit), 255 },
> > +    { SCMP_SYS(uselib), 255 },
> > +    { SCMP_SYS(ustat), 255 },
> > +    { SCMP_SYS(vserver), 255 },
> > +};
> > +
> >  static const struct QemuSeccompSyscall blacklist[] = {
> >      { SCMP_SYS(reboot), 255 },
> >      { SCMP_SYS(swapon), 255 },
> > @@ -56,7 +85,20 @@ static const struct QemuSeccompSyscall blacklist[] = {
> >      { SCMP_SYS(vserver), 255 },
> >  };
> >  
> > -int seccomp_start(void)
> > +static int is_obsolete(int syscall)
> > +{
> > +    unsigned int i = 0;
> > +
> > +    for (i = 0; i < ARRAY_SIZE(obsolete); i++) {
> > +        if (syscall == obsolete[i].num) {
> > +            return 1;
> > +        }
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> > +int seccomp_start(uint8_t seccomp_opts)
> >  {
> >      int rc = 0;
> >      unsigned int i = 0;
> > @@ -69,6 +111,9 @@ int seccomp_start(void)
> >      }
> >  
> >      for (i = 0; i < ARRAY_SIZE(blacklist); i++) {
> > +        if ((seccomp_opts & OBSOLETE) && is_obsolete(blacklist[i].num)) {
> > +            continue;
> > +        }
> >          rc = seccomp_rule_add(ctx, SCMP_ACT_KILL, blacklist[i].num, 0);
> >          if (rc < 0) {
> >              goto seccomp_return;
> > diff --git a/vl.c b/vl.c
> > index 1a95500ac7..7b08b3383b 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -269,6 +269,10 @@ static QemuOptsList qemu_sandbox_opts = {
> >              .name = "enable",
> >              .type = QEMU_OPT_BOOL,
> >          },
> > +        {
> > +            .name = "obsolete",
> > +            .type = QEMU_OPT_STRING,
> > +        },
> 
> Since this is basically a boolean switch, could you maybe rather use
> "QEMU_OPT_BOOL" here, too (and also in the following patches)? I think
> it is also easier for the users to memorize "obsolete=on" instead of
> yet-another-parameter-syntax like "obsolete=allow".
> 

Yes, that's definitely in my mind. I just wanted to make the first
draft the same way Daniel designed and evolve from there.

-- 
Eduardo Otubo
ProfitBricks GmbH