[kernel-hardening] Re: [PATCH v11 10/12] ptrace,seccomp: Add PTRACE_SECCOMP support

[Oleg Nesterov <oleg@redhat.com>]

On 02/24, Will Drewry wrote:
>
>  arch/Kconfig              |    1 +
>  include/linux/ptrace.h    |    7 +++++--
>  include/linux/seccomp.h   |    4 +++-
>  include/linux/tracehook.h |    6 ++++++
>  kernel/ptrace.c           |    4 ++++
>  kernel/seccomp.c          |   18 ++++++++++++++++++

FYI, this conflicts with the changes -mm tree.

The changes in ptrace.* confict with Denys's
"ptrace: simplify PTRACE_foo constants and PTRACE_SETOPTIONS code"

The change in tracehook.h conflicts with
"ptrace: the killed tracee should not enter the syscall"

> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -354,6 +354,24 @@ int __secure_computing_int(int this_syscall)
>  			seccomp_send_sigsys(this_syscall, reason_code);
>  			return -1;
>  		}
> +		case SECCOMP_RET_TRACE: {
> +			int ret;
> +			struct pt_regs *regs = task_pt_regs(current);
> +			if (!(test_tsk_thread_flag(current, TIF_SYSCALL_TRACE)) ||
> +			    !(current->ptrace & PT_TRACE_SECCOMP))
> +				return -1;
> +			/*
> +			 * PT_TRACE_SECCOMP and seccomp.trace indicate whether
> +			 * tracehook_report_syscall_entry needs to signal the
> +			 * tracer.  This avoids race conditions in hand off and
> +			 * the requirement for TIF_SYSCALL_TRACE ensures that
> +			 * we are in the syscall slow path.
> +			 */
> +			current->seccomp.trace = 1;
> +			ret = tracehook_report_syscall_entry(regs);
> +			current->seccomp.trace = 0;
> +			return ret;

To be honest, this interface looks a bit strange to me...

Once again, sorry if this was already discussed. But perhaps it would
be better to introduce PTRACE_EVENT_SECCOMP/PTRACE_O_SECCOMP instead?

SECCOMP_RET_TRACE: could simply do ptrace_event(PTRACE_EVENT_SECCOMP)
unconditionaly. The tracer can set the option and do PTRACE_CONT if it
doesn't want the system call notifications.

This is also much simpler, no need to change ptrace/tracehook files.

Oleg.