linux-user: fix emulation of splice syscall

The second and fourth argument are in/out parameters, store them back
after the syscall.  Also, the fourth argument was mishandled, and EFAULT
handling was missing.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/syscall.c

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 5720195..4bd9543 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -9351,15 +9351,29 @@
         {
             loff_t loff_in, loff_out;
             loff_t *ploff_in = NULL, *ploff_out = NULL;
-            if(arg2) {
-                get_user_u64(loff_in, arg2);
+            if (arg2) {
+                if (get_user_u64(loff_in, arg2)) {
+                    goto efault;
+                }
                 ploff_in = &loff_in;
             }
-            if(arg4) {
-                get_user_u64(loff_out, arg2);
+            if (arg4) {
+                if (get_user_u64(loff_out, arg4)) {
+                    goto efault;
+                }
                 ploff_out = &loff_out;
             }
             ret = get_errno(splice(arg1, ploff_in, arg3, ploff_out, arg5, arg6));
+            if (arg2) {
+                if (put_user_u64(loff_in, arg2)) {
+                    goto efault;
+                }
+            }
+            if (arg4) {
+                if (put_user_u64(loff_out, arg4)) {
+                    goto efault;
+                }
+            }
         }
         break;
 #endif