fuse: verify write return

Make sure filesystem is not returning a bogus number of bytes written.

Fixes: ea9b9907 ("fuse: implement perform_write")
Cc: <stable@vger.kernel.org> # v2.6.26
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -1096,6 +1096,8 @@ static ssize_t fuse_send_write_pages(struct fuse_io_args *ia,
 	ia->write.in.flags = fuse_write_flags(iocb);
 
 	err = fuse_simple_request(fc, &ap->args);
+	if (!err && ia->write.out.size > count)
+		err = -EIO;
 
 	offset = ap->descs[0].offset;
 	count = ia->write.out.size;