[PATCH] ptrace: take into account saved_sigmask in PTRACE_{GET,SET}SIGMASK

[Andrei Vagin <avagin@gmail.com>]

There are a few system calls (pselect, ppoll, etc) which replace a task
sigmask while they are running in a kernel-space

When a task calls one of these syscalls, the kernel saves a current
sigmask in task->saved_sigmask and sets a syscall sigmask.

On syscall-exit-stop, ptrace traps a task before restoring the
saved_sigmask, so PTRACE_GETSIGMASK returns the syscall sigmask and
PTRACE_SETSIGMASK does nothing, because its sigmask is replaced by
saved_sigmask, when the task returns to user-space.

This patch fixes this problem. PTRACE_GET_SIGMASK returns saved_sigmask
is it's set. PTRACE_SETSIGMASK drops the TIF_RESTORE_SIGMASK flag.

Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: 29000caecbe8 ("ptrace: add ability to get/set signal-blocked mask")
Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 include/linux/sched/signal.h | 18 ++++++++++++++++++
 kernel/ptrace.c              | 15 +++++++++++++--
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 1be35729c2c5..660d78c9af6c 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -417,10 +417,20 @@ static inline void set_restore_sigmask(void)
 	set_thread_flag(TIF_RESTORE_SIGMASK);
 	WARN_ON(!test_thread_flag(TIF_SIGPENDING));
 }
+
+static inline void clear_tsk_restore_sigmask(struct task_struct *tsk)
+{
+	clear_tsk_thread_flag(tsk, TIF_RESTORE_SIGMASK);
+}
+
 static inline void clear_restore_sigmask(void)
 {
 	clear_thread_flag(TIF_RESTORE_SIGMASK);
 }
+static inline bool test_tsk_restore_sigmask(struct task_struct *tsk)
+{
+	return test_tsk_thread_flag(tsk, TIF_RESTORE_SIGMASK);
+}
 static inline bool test_restore_sigmask(void)
 {
 	return test_thread_flag(TIF_RESTORE_SIGMASK);
@@ -438,6 +448,10 @@ static inline void set_restore_sigmask(void)
 	current->restore_sigmask = true;
 	WARN_ON(!test_thread_flag(TIF_SIGPENDING));
 }
+static inline void clear_tsk_restore_sigmask(struct task_struct *tsk)
+{
+	tsk->restore_sigmask = false;
+}
 static inline void clear_restore_sigmask(void)
 {
 	current->restore_sigmask = false;
@@ -446,6 +460,10 @@ static inline bool test_restore_sigmask(void)
 {
 	return current->restore_sigmask;
 }
+static inline bool test_tsk_restore_sigmask(struct task_struct *tsk)
+{
+	return tsk->restore_sigmask;
+}
 static inline bool test_and_clear_restore_sigmask(void)
 {
 	if (!current->restore_sigmask)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 21fec73d45d4..fc0d667f5792 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -29,6 +29,7 @@
 #include <linux/hw_breakpoint.h>
 #include <linux/cn_proc.h>
 #include <linux/compat.h>
+#include <linux/sched/signal.h>
 
 /*
  * Access another process' address space via ptrace.
@@ -925,18 +926,26 @@ int ptrace_request(struct task_struct *child, long request,
 			ret = ptrace_setsiginfo(child, &siginfo);
 		break;
 
-	case PTRACE_GETSIGMASK:
+	case PTRACE_GETSIGMASK: {
+		sigset_t *mask;
+
 		if (addr != sizeof(sigset_t)) {
 			ret = -EINVAL;
 			break;
 		}
 
-		if (copy_to_user(datavp, &child->blocked, sizeof(sigset_t)))
+		if (test_tsk_restore_sigmask(child))
+			mask = &child->saved_sigmask;
+		else
+			mask = &child->blocked;
+
+		if (copy_to_user(datavp, mask, sizeof(sigset_t)))
 			ret = -EFAULT;
 		else
 			ret = 0;
 
 		break;
+	}
 
 	case PTRACE_SETSIGMASK: {
 		sigset_t new_set;
@@ -962,6 +971,8 @@ int ptrace_request(struct task_struct *child, long request,
 		child->blocked = new_set;
 		spin_unlock_irq(&child->sighand->siglock);
 
+		clear_tsk_restore_sigmask(child);
+
 		ret = 0;
 		break;
 	}
-- 
2.17.2