From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47280) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dqHGQ-0004F1-4E for qemu-devel@nongnu.org; Fri, 08 Sep 2017 07:16:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dqHGL-0002T7-1V for qemu-devel@nongnu.org; Fri, 08 Sep 2017 07:15:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39286) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dqHGK-0002Sc-Oh for qemu-devel@nongnu.org; Fri, 08 Sep 2017 07:15:52 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DC0A35F7B9 for ; Fri, 8 Sep 2017 11:15:51 +0000 (UTC) Date: Fri, 8 Sep 2017 13:15:46 +0200 From: Eduardo Otubo Message-ID: <20170908111546.GA13739@vader> References: <20170908091027.9104-1-otubo@redhat.com> <20170908091027.9104-5-otubo@redhat.com> <2ebb2804-a613-0942-ee9b-aa900093ac98@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <2ebb2804-a613-0942-ee9b-aa900093ac98@redhat.com> Subject: Re: [Qemu-devel] [PATCHv5 4/5] seccomp: add spawn argument to command line List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Thomas Huth Cc: qemu-devel@nongnu.org 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 > > --- > > 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 > > > > 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 > > -@item -sandbox @var{arg}[,obsolete=@var{string}][,elevateprivileges=@var{string}] > > +@item -sandbox @var{arg}[,obsolete=@var{string}][,elevateprivileges=@var{string}][,spawn=@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'. > > @@ -4037,6 +4040,8 @@ disable it. The default is 'off'. > > Enable Obsolete system calls > > @item elevateprivileges=@var{string} > > Disable set*uid|gid system calls > > +@item spawn=@var{string} > > +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