fuse: ioctl: translate ENOSYS in outarg

Fuse shouldn't return ENOSYS from its ioctl implementation. If userspace
responds with ENOSYS it should be translated to ENOTTY.

There are two ways to return an error from the IOCTL request:

 - fuse_out_header.error
 - fuse_ioctl_out.result

Commit 02c0cab8 ("fuse: ioctl: translate ENOSYS") already fixed this
issue for the first case, but missed the second case.  This patch fixes the
second case.
Reported-by: Jonathan Katz <jkatz@eitmlabs.org>
Closes: https://lore.kernel.org/all/CALKgVmcC1VUV_gJVq70n--omMJZUb4HSh_FqvLTHgNBc+HCLFQ@mail.gmail.com/
Fixes: 02c0cab8 ("fuse: ioctl: translate ENOSYS")
Cc: <stable@vger.kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/ioctl.c

@@ -9,14 +9,23 @@
 #include <linux/compat.h>
 #include <linux/fileattr.h>
 
-static ssize_t fuse_send_ioctl(struct fuse_mount *fm, struct fuse_args *args)
+static ssize_t fuse_send_ioctl(struct fuse_mount *fm, struct fuse_args *args,
+			       struct fuse_ioctl_out *outarg)
 {
-	ssize_t ret = fuse_simple_request(fm, args);
+	ssize_t ret;
+
+	args->out_args[0].size = sizeof(*outarg);
+	args->out_args[0].value = outarg;
+
+	ret = fuse_simple_request(fm, args);
 
 	/* Translate ENOSYS, which shouldn't be returned from fs */
 	if (ret == -ENOSYS)
 		ret = -ENOTTY;
 
+	if (ret >= 0 && outarg->result == -ENOSYS)
+		outarg->result = -ENOTTY;
+
 	return ret;
 }
 
@@ -264,13 +273,11 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 	}
 
 	ap.args.out_numargs = 2;
-	ap.args.out_args[0].size = sizeof(outarg);
-	ap.args.out_args[0].value = &outarg;
 	ap.args.out_args[1].size = out_size;
 	ap.args.out_pages = true;
 	ap.args.out_argvar = true;
 
-	transferred = fuse_send_ioctl(fm, &ap.args);
+	transferred = fuse_send_ioctl(fm, &ap.args, &outarg);
 	err = transferred;
 	if (transferred < 0)
 		goto out;
@@ -399,12 +406,10 @@ static int fuse_priv_ioctl(struct inode *inode, struct fuse_file *ff,
 	args.in_args[1].size = inarg.in_size;
 	args.in_args[1].value = ptr;
 	args.out_numargs = 2;
-	args.out_args[0].size = sizeof(outarg);
-	args.out_args[0].value = &outarg;
 	args.out_args[1].size = inarg.out_size;
 	args.out_args[1].value = ptr;
 
-	err = fuse_send_ioctl(fm, &args);
+	err = fuse_send_ioctl(fm, &args, &outarg);
 	if (!err) {
 		if (outarg.result < 0)
 			err = outarg.result;