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

PATCH RESEND In review Andrei Vagin 4 participants 4 messages Mar 19, 2019 – Mar 20, 2019 ptrace support

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Andrei Vagin

author

2019-03-19 19:20 UTC #0 lore raw

PATCH RESEND 1/1 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_GET_SIGMASK returns saved_sigmask is it's set. PTRACE_SETSIGMASK drops the TIF_RESTORE_SIGMASK flag.

Link http://lkml.kernel.org/r/[email protected] open here

Fixes 29000caecbe8 ("ptrace: add ability to get/set signal-blocked mask")

Signed-off-by Andrei Vagin <[email protected]>

Cc Oleg Nesterov <[email protected]>

Cc "Eric W. Biederman" <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

Signed-off-by Stephen Rothwell <[email protected]>

---

Hello Andrew,

This patch is in a queue for a long time and it looks like you are waiting ack from Oleg. He said the patch is fine:
https://www.spinics.net/lists/kernel/msg2972154.html

And promised to send a formal ack in reply to this email.

 include/linux/sched/signal.h | 18 ++++++++++++++++++
 kernel/ptrace.c              | 15 +++++++++++++--
 2 files changed, 31 insertions(+), 2 deletions(-)

include/linux/sched/signal.h +18 -0

index ae5655197698..e412c092c1e8 100644
@@ -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)

kernel/ptrace.c +13 -2

index 771e93f9c43f..6f357f4fc859 100644
@@ -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;
 	}

Signature · 1 line

2.20.1

Dmitry V. Levin

2019-03-19 22:32 UTC #1 lore raw

Quoted 6 lines · Andrei Vagin

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.

Quoted 7 lines

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.

If it's not too late, could somebody tweak the commit message so that PTRACE_GET_SIGMASK becomes PTRACE_GETSIGMASK and "is it's set" is changed to "if it's set", please?

Signature · 1 line

ldv

Andrew Morton

2019-03-19 22:58 UTC #2 lore raw

Quoted 12 lines · On Wed, 20 Mar 2019 01:32:53 +0300 "Dmitry V. Levin" <[email protected]> wrote:

Quoted 11 lines · Andrei Vagin
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.

Quoted 6 lines

Quoted 2 lines
This patch fixes this problem. PTRACE_GET_SIGMASK returns saved_sigmask is it's set. PTRACE_SETSIGMASK drops the TIF_RESTORE_SIGMASK flag.
If it's not too late, could somebody tweak the commit message so that PTRACE_GET_SIGMASK becomes PTRACE_GETSIGMASK and "is it's set" is changed to "if it's set", please?

I made those changes to my copy.

Oleg Nesterov

maintainer Acked-by on v1 1/1

2019-03-20 13:27 UTC #3 lore raw

In reply to Andrei Vagin

Quoted 7 lines · Andrei Vagin

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.

Quoted 7 lines

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.

Acked-by Oleg Nesterov <[email protected]>