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Re: [Qemu-devel] [PATCHv5 4/5] seccomp: add spawn argument to command li
From: |
Eduardo Otubo |
Subject: |
Re: [Qemu-devel] [PATCHv5 4/5] seccomp: add spawn argument to command line |
Date: |
Fri, 8 Sep 2017 13:15:46 +0200 |
User-agent: |
Mutt/1.8.3+47 (5f034395e53d) (2017-05-23) |
On Fri, Sep 08, 2017 at 11:50:12AM +0200, Thomas Huth wrote:
> On 08.09.2017 11:10, Eduardo Otubo wrote:
> > This patch adds [,spawn=deny] argument to `-sandbox on' option. It
> > blacklists fork and execve system calls, avoiding Qemu to spawn new
> > threads or processes.
> >
> > Signed-off-by: Eduardo Otubo <address@hidden>
> > ---
> > include/sysemu/seccomp.h | 1 +
> > qemu-options.hx | 9 +++++++--
> > qemu-seccomp.c | 12 ++++++++++++
> > vl.c | 16 ++++++++++++++++
> > 4 files changed, 36 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/sysemu/seccomp.h b/include/sysemu/seccomp.h
> > index 4a9e63c7cd..3ab5fc4f61 100644
> > --- a/include/sysemu/seccomp.h
> > +++ b/include/sysemu/seccomp.h
> > @@ -18,6 +18,7 @@
> > #define QEMU_SECCOMP_SET_DEFAULT (1 << 0)
> > #define QEMU_SECCOMP_SET_OBSOLETE (1 << 1)
> > #define QEMU_SECCOMP_SET_PRIVILEGED (1 << 2)
> > +#define QEMU_SECCOMP_SET_SPAWN (1 << 3)
> >
> > #include <seccomp.h>
> >
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 5c1b163fb5..2b04b9f170 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -4018,6 +4018,7 @@ ETEXI
> >
> > DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \
> > "-sandbox
> > on[,obsolete=allow|deny][,elevateprivileges=allow|deny|children]\n" \
> > + " [,spawn=allow|deny]\n" \
> > " Enable seccomp mode 2 system call filter (default
> > 'off').\n" \
> > " use 'obsolete' to allow obsolete system calls that
> > are provided\n" \
> > " by the kernel, but typically no longer used by
> > modern\n" \
> > @@ -4025,10 +4026,12 @@ DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \
> > " use 'elevateprivileges' to allow or deny QEMU process
> > to elevate\n" \
> > " its privileges by blacklisting all set*uid|gid
> > system calls.\n" \
> > " The value 'children' will deny set*uid|gid system
> > calls for\n" \
> > - " main QEMU process but will allow forks and
> > execves to run unprivileged\n",
> > + " main QEMU process but will allow forks and
> > execves to run unprivileged\n" \
> > + " use 'spawn' to avoid QEMU to spawn new threads or
> > processes by\n" \
> > + " blacklisting *fork and execve\n",
> > QEMU_ARCH_ALL)
> > STEXI
> > address@hidden -sandbox @var{arg}[,address@hidden,address@hidden
> > address@hidden -sandbox
> > @var{arg}[,address@hidden,address@hidden,address@hidden
> > @findex -sandbox
> > Enable Seccomp mode 2 system call filter. 'on' will enable syscall
> > filtering and 'off' will
> > disable it. The default is 'off'.
> > @@ -4037,6 +4040,8 @@ disable it. The default is 'off'.
> > Enable Obsolete system calls
> > @item address@hidden
> > Disable set*uid|gid system calls
> > address@hidden address@hidden
> > +Disable *fork and execve
> > @end table
> > ETEXI
> >
> > diff --git a/qemu-seccomp.c b/qemu-seccomp.c
> > index 2bad16cafb..4c169febf8 100644
> > --- a/qemu-seccomp.c
> > +++ b/qemu-seccomp.c
> > @@ -79,6 +79,10 @@ static const struct QemuSeccompSyscall blacklist[] = {
> > { SCMP_SYS(setresgid), 4, QEMU_SECCOMP_SET_PRIVILEGED },
> > { SCMP_SYS(setfsuid), 4, QEMU_SECCOMP_SET_PRIVILEGED },
> > { SCMP_SYS(setfsgid), 4, QEMU_SECCOMP_SET_PRIVILEGED },
> > + /* spawn */
> > + { SCMP_SYS(fork), 8, QEMU_SECCOMP_SET_SPAWN },
> > + { SCMP_SYS(vfork), 8, QEMU_SECCOMP_SET_SPAWN },
> > + { SCMP_SYS(execve), 8, QEMU_SECCOMP_SET_SPAWN },
> > };
> >
> >
> > @@ -109,6 +113,14 @@ int seccomp_start(uint32_t seccomp_opts)
> > }
> >
> > break;
> > + case QEMU_SECCOMP_SET_SPAWN:
> > + if (seccomp_opts & QEMU_SECCOMP_SET_SPAWN) {
> > + break;
> > + } else {
> > + continue;
> > + }
> > +
>
> Remove the above empty line?
>
> Anyway, it's somewhat ugly that you need a switch-case statement here at
> all. Couldn't you simply check it like this:
>
> if (!(seccomp_opts & blacklist[i].set)) {
> continue;
> }
> ?
>
> You then just have to invert the meaning of the
> QEMU_SECCOMP_SET_OBSOLETE bit in the second patch, so that this bit is
> treated in the same way as the others (i.e. use
> uint32_t seccomp_opts = QEMU_SECCOMP_SET_OBSOLETE;
> instead of
> uint32_t seccomp_opts = 0x00000;
> in vl.c in the second patch).
That's indeed much better, but perhaps:
uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT | QEMU_SECCOMP_SET_OBSOLETE;
?
--
Eduardo Otubo
Senior Software Engineer @ RedHat
- Re: [Qemu-devel] [PATCHv5 1/5] seccomp: changing from whitelist to blacklist, (continued)
[Qemu-devel] [PATCHv5 2/5] seccomp: add obsolete argument to command line, Eduardo Otubo, 2017/09/08
[Qemu-devel] [PATCHv5 4/5] seccomp: add spawn argument to command line, Eduardo Otubo, 2017/09/08
[Qemu-devel] [PATCHv5 3/5] seccomp: add elevateprivileges argument to command line, Eduardo Otubo, 2017/09/08
[Qemu-devel] [PATCHv5 5/5] seccomp: add resourcecontrol argument to command line, Eduardo Otubo, 2017/09/08