[PATCH 4.9 049/153] sigaltstack: support SS_AUTODISARM for CONFIG_COMPAT

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stas Sergeev <stsp@xxxxxxx>

commit 441398d378f29a5ad6d0fcda07918e54e4961800 upstream.

Currently SS_AUTODISARM is not supported in compatibility mode, but does
not return -EINVAL either.  This makes dosemu built with -m32 on x86_64
to crash.  Also the kernel's sigaltstack selftest fails if compiled with
-m32.

This patch adds the needed support.

Link: http://lkml.kernel.org/r/20170205101213.8163-2-stsp@xxxxxxx
Signed-off-by: Stas Sergeev <stsp@xxxxxxxxxxxxxxxxxxxxx>
Cc: Milosz Tanski <milosz@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
Cc: Waiman Long <Waiman.Long@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
Cc: Wang Xiaoqiang <wangxq10@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 include/linux/compat.h |    4 +++-
 kernel/signal.c        |   11 +++++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -711,8 +711,10 @@ int __compat_save_altstack(compat_stack_
 	compat_stack_t __user *__uss = uss; \
 	struct task_struct *t = current; \
 	put_user_ex(ptr_to_compat((void __user *)t->sas_ss_sp), &__uss->ss_sp); \
-	put_user_ex(sas_ss_flags(sp), &__uss->ss_flags); \
+	put_user_ex(t->sas_ss_flags, &__uss->ss_flags); \
 	put_user_ex(t->sas_ss_size, &__uss->ss_size); \
+	if (t->sas_ss_flags & SS_AUTODISARM) \
+		sas_ss_reset(t); \
 } while (0);
 
 asmlinkage long compat_sys_sched_rr_get_interval(compat_pid_t pid,
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3226,10 +3226,17 @@ int compat_restore_altstack(const compat
 
 int __compat_save_altstack(compat_stack_t __user *uss, unsigned long sp)
 {
+	int err;
 	struct task_struct *t = current;
-	return  __put_user(ptr_to_compat((void __user *)t->sas_ss_sp), &uss->ss_sp) |
-		__put_user(sas_ss_flags(sp), &uss->ss_flags) |
+	err = __put_user(ptr_to_compat((void __user *)t->sas_ss_sp),
+			 &uss->ss_sp) |
+		__put_user(t->sas_ss_flags, &uss->ss_flags) |
 		__put_user(t->sas_ss_size, &uss->ss_size);
+	if (err)
+		return err;
+	if (t->sas_ss_flags & SS_AUTODISARM)
+		sas_ss_reset(t);
+	return 0;
 }
 #endif