On Mon, Feb 27, 2012 at 11:54 AM, Oleg Nesterov [off-list ref] wrote:

On 02/24, Will Drewry wrote:

quoted

 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"

What's the best way to reconcile this in this day and age? I don't see
these in kernel-next yet and I can't tell if there is a public -mm
anywhere anymore.  I can use the patches from the mailing list with
Denys's changes if that'd be good enough.  His cleanup will make this
code even smaller!

quoted

--- 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.

Works for me - this also gets rid of the extra int for brief state
tracking. I'll switch over to that in the next rev.  (More follow-ups
to your reviews incoming too :).

Thanks!
will