Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751844AbbFMXyF (ORCPT ); Sat, 13 Jun 2015 19:54:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50635 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751237AbbFMXx5 (ORCPT ); Sat, 13 Jun 2015 19:53:57 -0400 Date: Sun, 14 Jun 2015 01:52:50 +0200 From: Oleg Nesterov To: Tycho Andersen Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Kees Cook , Andy Lutomirski , Will Drewry , Roland McGrath , Pavel Emelyanov , "Serge E. Hallyn" Subject: Re: [PATCH v5] seccomp: add ptrace options for suspend/resume Message-ID: <20150613235250.GA25252@redhat.com> References: <1434207768-16729-1-git-send-email-tycho.andersen@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1434207768-16729-1-git-send-email-tycho.andersen@canonical.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5812 Lines: 155 On 06/13, Tycho Andersen wrote: > > This patch is the first step in enabling checkpoint/restore of processes > with seccomp enabled. So just in case, I am fine with this version. > One of the things CRIU does while dumping tasks is inject code into them > via ptrace to collect information that is only available to the process > itself. However, if we are in a seccomp mode where these processes are > prohibited from making these syscalls, then what CRIU does kills the task. > > This patch adds a new ptrace option, PTRACE_O_SUSPEND_SECCOMP, that enables > a task from the init user namespace which has CAP_SYS_ADMIN and no seccomp > filters to disable (and re-enable) seccomp filters for another task so that > they can be successfully dumped (and restored). We restrict the set of > processes that can disable seccomp through ptrace because although today > ptrace can be used to bypass seccomp, there is some discussion of closing > this loophole in the future and we would like this patch to not depend on > that behavior and be future proofed for when it is removed. > > Note that seccomp can be suspended before any filters are actually > installed; this behavior is useful on criu restore, so that we can suspend > seccomp, restore the filters, unmap our restore code from the restored > process' address space, and then resume the task by detaching and have the > filters resumed as well. > > v2 changes: > > * require that the tracer have no seccomp filters installed > * drop TIF_NOTSC manipulation from the patch > * change from ptrace command to a ptrace option and use this ptrace option > as the flag to check. This means that as soon as the tracer > detaches/dies, seccomp is re-enabled and as a corrollary that one can not > disable seccomp across PTRACE_ATTACHs. > > v3 changes: > > * get rid of various #ifdefs everywhere > * report more sensible errors when PTRACE_O_SUSPEND_SECCOMP is incorrectly > used > > v4 changes: > > * get rid of may_suspend_seccomp() in favor of a capable() check in ptrace > directly > > v5 changes: > > * check that seccomp is not enabled (or suspended) on the tracer > > Signed-off-by: Tycho Andersen > CC: Kees Cook > CC: Andy Lutomirski > CC: Will Drewry > CC: Roland McGrath > CC: Oleg Nesterov > CC: Pavel Emelyanov > CC: Serge E. Hallyn > --- > include/linux/ptrace.h | 1 + > include/uapi/linux/ptrace.h | 6 ++++-- > kernel/ptrace.c | 13 +++++++++++++ > kernel/seccomp.c | 8 ++++++++ > 4 files changed, 26 insertions(+), 2 deletions(-) > > diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h > index 987a73a..061265f 100644 > --- a/include/linux/ptrace.h > +++ b/include/linux/ptrace.h > @@ -34,6 +34,7 @@ > #define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP) > > #define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT) > +#define PT_SUSPEND_SECCOMP (PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT) > > /* single stepping state bits (used on ARM and PA-RISC) */ > #define PT_SINGLESTEP_BIT 31 > diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h > index cf1019e..a7a6979 100644 > --- a/include/uapi/linux/ptrace.h > +++ b/include/uapi/linux/ptrace.h > @@ -89,9 +89,11 @@ struct ptrace_peeksiginfo_args { > #define PTRACE_O_TRACESECCOMP (1 << PTRACE_EVENT_SECCOMP) > > /* eventless options */ > -#define PTRACE_O_EXITKILL (1 << 20) > +#define PTRACE_O_EXITKILL (1 << 20) > +#define PTRACE_O_SUSPEND_SECCOMP (1 << 21) > > -#define PTRACE_O_MASK (0x000000ff | PTRACE_O_EXITKILL) > +#define PTRACE_O_MASK (\ > + 0x000000ff | PTRACE_O_EXITKILL | PTRACE_O_SUSPEND_SECCOMP) > > #include > > diff --git a/kernel/ptrace.c b/kernel/ptrace.c > index c8e0e05..496028b 100644 > --- a/kernel/ptrace.c > +++ b/kernel/ptrace.c > @@ -556,6 +556,19 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data) > if (data & ~(unsigned long)PTRACE_O_MASK) > return -EINVAL; > > + if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) { > + if (!config_enabled(CONFIG_CHECKPOINT_RESTORE) || > + !config_enabled(CONFIG_SECCOMP)) > + return -EINVAL; > + > + if (!capable(CAP_SYS_ADMIN)) > + return -EPERM; > + > + if (current->seccomp.mode != SECCOMP_MODE_DISABLED || > + current->ptrace & PT_SUSPEND_SECCOMP) > + return -EPERM; > + } > + > /* Avoid intermediate state when all opts are cleared */ > flags = child->ptrace; > flags &= ~(PTRACE_O_MASK << PT_OPT_FLAG_SHIFT); > diff --git a/kernel/seccomp.c b/kernel/seccomp.c > index 980fd26..645e42d 100644 > --- a/kernel/seccomp.c > +++ b/kernel/seccomp.c > @@ -590,6 +590,10 @@ void secure_computing_strict(int this_syscall) > { > int mode = current->seccomp.mode; > > + if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && > + unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) > + return; > + > if (mode == 0) > return; > else if (mode == SECCOMP_MODE_STRICT) > @@ -691,6 +695,10 @@ u32 seccomp_phase1(struct seccomp_data *sd) > int this_syscall = sd ? sd->nr : > syscall_get_nr(current, task_pt_regs(current)); > > + if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && > + unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) > + return SECCOMP_PHASE1_OK; > + > switch (mode) { > case SECCOMP_MODE_STRICT: > __secure_computing_strict(this_syscall); /* may call do_exit */ > -- > 2.1.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/