ptrace: add ability to get/set signal-blocked mask

crtools uses a parasite code for dumping processes.  The parasite code is
injected into a process with help PTRACE_SEIZE.

Currently crtools blocks signals from a parasite code.  If a process has
pending signals, crtools wait while a process handles these signals.

This method is not suitable for stopped tasks.  A stopped task can have a
few pending signals, when we will try to execute a parasite code, we will
need to drop SIGSTOP, but all other signals must remain pending, because a
state of processes must not be changed during checkpointing.

This patch adds two ptrace commands to set/get signal-blocked mask.

I think gdb can use this commands too.

[akpm@linux-foundation.org: be consistent with brace layout]
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 45 insertions, 2 deletions

diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index 52ebcc89f306..cf1019e15f5b 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -61,6 +61,9 @@ struct ptrace_peeksiginfo_args {
         __s32 nr;       /* how may siginfos to take */
 };
 
+#define PTRACE_GETSIGMASK       0x420a
+#define PTRACE_SETSIGMASK       0x420b
+
 /* Read signals from a shared (process wide) queue */
 #define PTRACE_PEEKSIGINFO_SHARED       (1 << 0)
 
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 335a7ae697f5..ba5e6cea181a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -844,6 +844,47 @@ int ptrace_request(struct task_struct *child, long request,
                         ret = ptrace_setsiginfo(child, &siginfo);
                 break;
 
+        case PTRACE_GETSIGMASK:
+                if (addr != sizeof(sigset_t)) {
+                        ret = -EINVAL;
+                        break;
+                }
+
+                if (copy_to_user(datavp, &child->blocked, sizeof(sigset_t)))
+                        ret = -EFAULT;
+                else
+                        ret = 0;
+
+                break;
+
+        case PTRACE_SETSIGMASK: {
+                sigset_t new_set;
+
+                if (addr != sizeof(sigset_t)) {
+                        ret = -EINVAL;
+                        break;
+                }
+
+                if (copy_from_user(&new_set, datavp, sizeof(sigset_t))) {
+                        ret = -EFAULT;
+                        break;
+                }
+
+                sigdelsetmask(&new_set, sigmask(SIGKILL)|sigmask(SIGSTOP));
+
+                /*
+                 * Every thread does recalc_sigpending() after resume, so
+                 * retarget_shared_pending() and recalc_sigpending() are not
+                 * called here.
+                 */
+                spin_lock_irq(&child->sighand->siglock);
+                child->blocked = new_set;
+                spin_unlock_irq(&child->sighand->siglock);
+
+                ret = 0;
+                break;
+        }
+
         case PTRACE_INTERRUPT:
                 /*
                  * Stop tracee without any side-effect on signal or job
@@ -948,8 +989,7 @@ int ptrace_request(struct task_struct *child, long request,
 
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
         case PTRACE_GETREGSET:
-        case PTRACE_SETREGSET:
-        {
+        case PTRACE_SETREGSET: {
                 struct iovec kiov;
                 struct iovec __user *uiov = datavp;