ptrace: take into account saved_sigmask in PTRACE{GET,SET}SIGMASK

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_GETSIGMASK returns saved_sigmask
if it's set.  PTRACE_SETSIGMASK drops the TIF_RESTORE_SIGMASK flag.

Link: http://lkml.kernel.org/r/20181120060616.6043-1-avagin@gmail.com
Fixes: 29000caecbe8 ("ptrace: add ability to get/set signal-blocked mask")
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 31 insertions, 2 deletions

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index ae5655197698..e412c092c1e8 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -418,10 +418,20 @@ 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);
@@ -439,6 +449,10 @@ 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;
@@ -447,6 +461,10 @@ 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 771e93f9c43f..6f357f4fc859 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.
@@ -924,18 +925,26 @@ 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;
@@ -961,6 +970,8 @@ 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;
         }