[PATCH 14/22] introduce PT_SYSCALL_TRACE flag

[Oleg Nesterov]

Currently tracehooks assume that if the ptraced task has
TIF_SYSCALL_TRACE set, the tracee should report the syscall.
This is not true, this thread flag can be set by utrace.

Add the new internal ptrace flag, PT_SYSCALL_TRACE. Change
ptrace_set_syscall_trace() to set/clear this bit along with
TIF_SYSCALL_TRACE, change ptrace_report_syscall() to check
this flag instead of PT_PTRACED.

Signed-off-by: Oleg Nesterov <oleg at redhat.com>
---
 include/linux/ptrace.h    |    3 +++
 include/linux/tracehook.h |    2 +-
 kernel/ptrace.c           |    7 +++++--
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 9178d5c..98d995d 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -90,6 +90,8 @@
 
 #define PT_TRACE_MASK	0x000003f4
 
+#define PT_SYSCALL_TRACE	0x00010000
+
 /* single stepping state bits (used on ARM and PA-RISC) */
 #define PT_SINGLESTEP_BIT	31
 #define PT_SINGLESTEP		(1<<PT_SINGLESTEP_BIT)
@@ -187,6 +189,7 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
 	child->ptrace = 0;
 	if (unlikely(ptrace) && (current->ptrace & PT_PTRACED)) {
 		child->ptrace = current->ptrace;
+		child->ptrace &= ~PT_SYSCALL_TRACE;
 		__ptrace_link(child, current->parent);
 	}
 
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 3c7b6b3..6ce7a37 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -76,7 +76,7 @@ static inline void ptrace_report_syscall(struct pt_regs *regs)
 {
 	int ptrace = task_ptrace(current);
 
-	if (!(ptrace & PT_PTRACED))
+	if (!(ptrace & PT_SYSCALL_TRACE))
 		return;
 
 	ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index b6fd922..0825a01 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -39,10 +39,13 @@ static void ptrace_signal_wake_up(struct task_struct *p, int quiescent)
 
 static void ptrace_set_syscall_trace(struct task_struct *p, bool on)
 {
-	if (on)
+	if (on) {
+		p->ptrace |= PT_SYSCALL_TRACE;
 		set_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
-	else
+	} else {
+		p->ptrace &= ~PT_SYSCALL_TRACE;
 		clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
+	}
 }
 
 /*
-- 
1.5.5.1