[PATCH 22/31] 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 6d9282a..c10f610 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -104,6 +104,8 @@
 
 #define PT_TRACE_MASK	0x000003f4
 
+#define PT_SYSCALL_TRACE	0x00020000
+
 /* single stepping state bits (used on ARM and PA-RISC) */
 #define PT_SINGLESTEP_BIT	31
 #define PT_SINGLESTEP		(1<<PT_SINGLESTEP_BIT)
@@ -227,6 +229,7 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
 
 	if (unlikely(ptrace) && current->ptrace) {
 		child->ptrace = current->ptrace;
+		child->ptrace &= ~PT_SYSCALL_TRACE;
 		__ptrace_link(child, current->parent);
 
 		if (child->ptrace & PT_SEIZED)
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index ec2af67..eb9fe30 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -59,7 +59,7 @@ static inline void ptrace_report_syscall(struct pt_regs *regs)
 {
 	int ptrace = current->ptrace;
 
-	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 dc2ad34..7deb292 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -40,10 +40,13 @@ 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);
+	}
 }
 
 static int ptrace_trapping_sleep_fn(void *flags)
-- 
1.5.5.1