ptrace: kill clone/exec tracehooks

At this point, tracehooks aren't useful to mainline kernel and mostly
just add an extra layer of obfuscation.  Although they have comments,
without actual in-kernel users, it is difficult to tell what are their
assumptions and they're actually trying to achieve.  To mainline
kernel, they just aren't worth keeping around.

This patch kills the following clone and exec related tracehooks.

	tracehook_prepare_clone()
	tracehook_finish_clone()
	tracehook_report_clone()
	tracehook_report_clone_complete()
	tracehook_unsafe_exec()

The changes are mostly trivial - logic is moved to the caller and
comments are merged and adjusted appropriately.

The only exception is in check_unsafe_exec() where LSM_UNSAFE_PTRACE*
are OR'd to bprm->unsafe instead of setting it, which produces the
same result as the field is always zero on entry.  It also tests
p->ptrace instead of (p->ptrace & PT_PTRACED) for consistency, which
also gives the same result.

This doesn't introduce any behavior change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>

1 files changed, 32 insertions, 9 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index d4f0dff9d617..3c72a5b321a7 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1340,7 +1340,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         }
 
         if (likely(p->pid)) {
-                tracehook_finish_clone(p, clone_flags, trace);
+                ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
 
                 if (thread_group_leader(p)) {
                         if (is_child_reaper(pid))
@@ -1481,10 +1481,22 @@ long do_fork(unsigned long clone_flags,
         }
 
         /*
-         * When called from kernel_thread, don't do user tracing stuff.
+         * Determine whether and which event to report to ptracer.  When
+         * called from kernel_thread or CLONE_UNTRACED is explicitly
+         * requested, no event is reported; otherwise, report if the event
+         * for the type of forking is enabled.
          */
-        if (likely(user_mode(regs)))
-                trace = tracehook_prepare_clone(clone_flags);
+        if (likely(user_mode(regs)) && !(clone_flags & CLONE_UNTRACED)) {
+                if (clone_flags & CLONE_VFORK)
+                        trace = PTRACE_EVENT_VFORK;
+                else if ((clone_flags & CSIGNAL) != SIGCHLD)
+                        trace = PTRACE_EVENT_CLONE;
+                else
+                        trace = PTRACE_EVENT_FORK;
+
+                if (likely(!ptrace_event_enabled(current, trace)))
+                        trace = 0;
+        }
 
         p = copy_process(clone_flags, stack_start, regs, stack_size,
                          child_tidptr, NULL, trace);
@@ -1508,20 +1520,31 @@ long do_fork(unsigned long clone_flags,
                 }
 
                 audit_finish_fork(p);
-                tracehook_report_clone(regs, clone_flags, nr, p);
+
+                /*
+                 * Child is ready but hasn't started running yet.  Queue
+                 * SIGSTOP if it's gonna be ptraced - it doesn't matter who
+                 * attached/attaching to this task, the pending SIGSTOP is
+                 * right in any case.
+                 */
+                if (unlikely(p->ptrace)) {
+                        sigaddset(&p->pending.signal, SIGSTOP);
+                        set_tsk_thread_flag(p, TIF_SIGPENDING);
+                }
 
                 /*
                  * We set PF_STARTING at creation in case tracing wants to
                  * use this to distinguish a fully live task from one that
-                 * hasn't gotten to tracehook_report_clone() yet.  Now we
-                 * clear it and set the child going.
+                 * hasn't finished SIGSTOP raising yet.  Now we clear it
+                 * and set the child going.
                  */
                 p->flags &= ~PF_STARTING;
 
                 wake_up_new_task(p);
 
-                tracehook_report_clone_complete(trace, regs,
-                                                clone_flags, nr, p);
+                /* forking complete and child started to run, tell ptracer */
+                if (unlikely(trace))
+                        ptrace_event(trace, nr);
 
                 if (clone_flags & CLONE_VFORK) {
                         freezer_do_not_count();