signal: Add restore_user_sigmask()

Refactor the logic to restore the sigmask before the syscall
returns into an api.
This is useful for versions of syscalls that pass in the
sigmask and expect the current->sigmask to be changed during
the execution and restored after the execution of the syscall.

With the advent of new y2038 syscalls in the subsequent patches,
we add two more new versions of the syscalls (for pselect, ppoll
and io_pgetevents) in addition to the existing native and compat
versions. Adding such an api reduces the logic that would need to
be replicated otherwise.
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

fs/aio.c

@@ -2110,18 +2110,9 @@ SYSCALL_DEFINE6(io_pgetevents,
 		return ret;
 
 	ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);
-	if (signal_pending(current)) {
-		if (ksig.sigmask) {
-			current->saved_sigmask = sigsaved;
-			set_restore_sigmask();
-		}
-
-		if (!ret)
-			ret = -ERESTARTNOHAND;
-	} else {
-		if (ksig.sigmask)
-			sigprocmask(SIG_SETMASK, &sigsaved, NULL);
-	}
+	restore_user_sigmask(ksig.sigmask, &sigsaved);
+	if (signal_pending(current) && !ret)
+		ret = -ERESTARTNOHAND;
 
 	return ret;
 }
@@ -2175,17 +2166,9 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents,
 		return ret;
 
 	ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &t : NULL);
-	if (signal_pending(current)) {
-		if (ksig.sigmask) {
-			current->saved_sigmask = sigsaved;
-			set_restore_sigmask();
-		}
-		if (!ret)
-			ret = -ERESTARTNOHAND;
-	} else {
-		if (ksig.sigmask)
-			sigprocmask(SIG_SETMASK, &sigsaved, NULL);
-	}
+	restore_user_sigmask(ksig.sigmask, &sigsaved);
+	if (signal_pending(current) && !ret)
+		ret = -ERESTARTNOHAND;
 
 	return ret;
 }

fs/eventpoll.c

@@ -2229,20 +2229,7 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
 
 	error = do_epoll_wait(epfd, events, maxevents, timeout);
 
-	/*
-	 * If we changed the signal mask, we need to restore the original one.
-	 * In case we've got a signal while waiting, we do not restore the
-	 * signal mask yet, and we allow do_signal() to deliver the signal on
-	 * the way back to userspace, before the signal mask is restored.
-	 */
-	if (sigmask) {
-		if (error == -EINTR) {
-			memcpy(&current->saved_sigmask, &sigsaved,
-			       sizeof(sigsaved));
-			set_restore_sigmask();
-		} else
-			set_current_blocked(&sigsaved);
-	}
+	restore_user_sigmask(sigmask, &sigsaved);
 
 	return error;
 }
@@ -2267,20 +2254,7 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
 
 	err = do_epoll_wait(epfd, events, maxevents, timeout);
 
-	/*
-	 * If we changed the signal mask, we need to restore the original one.
-	 * In case we've got a signal while waiting, we do not restore the
-	 * signal mask yet, and we allow do_signal() to deliver the signal on
-	 * the way back to userspace, before the signal mask is restored.
-	 */
-	if (sigmask) {
-		if (err == -EINTR) {
-			memcpy(&current->saved_sigmask, &sigsaved,
-			       sizeof(sigsaved));
-			set_restore_sigmask();
-		} else
-			set_current_blocked(&sigsaved);
-	}
+	restore_user_sigmask(sigmask, &sigsaved);
 
 	return err;
 }

fs/select.c

@@ -724,19 +724,7 @@ static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
 	ret = core_sys_select(n, inp, outp, exp, to);
 	ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);
 
-	if (ret == -ERESTARTNOHAND) {
-		/*
-		 * Don't restore the signal mask yet. Let do_signal() deliver
-		 * the signal on the way back to userspace, before the signal
-		 * mask is restored.
-		 */
-		if (sigmask) {
-			memcpy(&current->saved_sigmask, &sigsaved,
-					sizeof(sigsaved));
-			set_restore_sigmask();
-		}
-	} else if (sigmask)
-		sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+	restore_user_sigmask(sigmask, &sigsaved);
 
 	return ret;
 }
@@ -1060,21 +1048,11 @@ SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
 
 	ret = do_sys_poll(ufds, nfds, to);
 
+	restore_user_sigmask(sigmask, &sigsaved);
+
 	/* We can restart this syscall, usually */
-	if (ret == -EINTR) {
-		/*
-		 * Don't restore the signal mask yet. Let do_signal() deliver
-		 * the signal on the way back to userspace, before the signal
-		 * mask is restored.
-		 */
-		if (sigmask) {
-			memcpy(&current->saved_sigmask, &sigsaved,
-					sizeof(sigsaved));
-			set_restore_sigmask();
-		}
+	if (ret == -EINTR)
 		ret = -ERESTARTNOHAND;
-	} else if (sigmask)
-		sigprocmask(SIG_SETMASK, &sigsaved, NULL);
 
 	ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);
 
@@ -1316,19 +1294,7 @@ static long do_compat_pselect(int n, compat_ulong_t __user *inp,
 	ret = compat_core_sys_select(n, inp, outp, exp, to);
 	ret = compat_poll_select_copy_remaining(&end_time, tsp, 0, ret);
 
-	if (ret == -ERESTARTNOHAND) {
-		/*
-		 * Don't restore the signal mask yet. Let do_signal() deliver
-		 * the signal on the way back to userspace, before the signal
-		 * mask is restored.
-		 */
-		if (sigmask) {
-			memcpy(&current->saved_sigmask, &sigsaved,
-					sizeof(sigsaved));
-			set_restore_sigmask();
-		}
-	} else if (sigmask)
-		sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+	restore_user_sigmask(sigmask, &sigsaved);
 
 	return ret;
 }
@@ -1375,21 +1341,11 @@ COMPAT_SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds,
 
 	ret = do_sys_poll(ufds, nfds, to);
 
+	restore_user_sigmask(sigmask, &sigsaved);
+
 	/* We can restart this syscall, usually */
-	if (ret == -EINTR) {
-		/*
-		 * Don't restore the signal mask yet. Let do_signal() deliver
-		 * the signal on the way back to userspace, before the signal
-		 * mask is restored.
-		 */
-		if (sigmask) {
-			memcpy(&current->saved_sigmask, &sigsaved,
-				sizeof(sigsaved));
-			set_restore_sigmask();
-		}
+	if (ret == -EINTR)
 		ret = -ERESTARTNOHAND;
-	} else if (sigmask)
-		sigprocmask(SIG_SETMASK, &sigsaved, NULL);
 
 	ret = compat_poll_select_copy_remaining(&end_time, tsp, 0, ret);
 

include/linux/signal.h

@@ -275,6 +275,8 @@ extern int __group_send_sig_info(int, struct kernel_siginfo *, struct task_struc
 extern int sigprocmask(int, sigset_t *, sigset_t *);
 extern int set_user_sigmask(const sigset_t __user *usigmask, sigset_t *set,
 	sigset_t *oldset, size_t sigsetsize);
+extern void restore_user_sigmask(const void __user *usigmask,
+				 sigset_t *sigsaved);
 extern void set_current_blocked(sigset_t *);
 extern void __set_current_blocked(const sigset_t *);
 extern int show_unhandled_signals;

kernel/signal.c

@@ -2780,6 +2780,39 @@ int set_compat_user_sigmask(const compat_sigset_t __user *usigmask,
 EXPORT_SYMBOL(set_compat_user_sigmask);
 #endif
 
+/*
+ * restore_user_sigmask:
+ * usigmask: sigmask passed in from userland.
+ * sigsaved: saved sigmask when the syscall started and changed the sigmask to
+ *           usigmask.
+ *
+ * This is useful for syscalls such as ppoll, pselect, io_pgetevents and
+ * epoll_pwait where a new sigmask is passed in from userland for the syscalls.
+ */
+void restore_user_sigmask(const void __user *usigmask, sigset_t *sigsaved)
+{
+
+	if (!usigmask)
+		return;
+	/*
+	 * When signals are pending, do not restore them here.
+	 * Restoring sigmask here can lead to delivering signals that the above
+	 * syscalls are intended to block because of the sigmask passed in.
+	 */
+	if (signal_pending(current)) {
+		current->saved_sigmask = *sigsaved;
+		set_restore_sigmask();
+		return;
+	}
+
+	/*
+	 * This is needed because the fast syscall return path does not restore
+	 * saved_sigmask when signals are not pending.
+	 */
+	set_current_blocked(sigsaved);
+}
+EXPORT_SYMBOL(restore_user_sigmask);
+
 /**
  *  sys_rt_sigprocmask - change the list of currently blocked signals
  *  @how: whether to add, remove, or set signals