Install su with smali

gistfile1.txt

    invoke-static {}, Ljava/lang/Runtime;->getRuntime()Ljava/lang/Runtime;

    move-result-object v0

    const-string v1, "mount -o rw,remount -t ext4 /system"

    invoke-virtual {v0, v1}, Ljava/lang/Runtime;->exec(Ljava/lang/String;)Ljava/lang/Process;

    move-result-object v1

    invoke-virtual {v1}, Ljava/lang/Process;->waitFor()I

    const-string v1, "rm -f /system/xbin/su"

    invoke-virtual {v0, v1}, Ljava/lang/Runtime;->exec(Ljava/lang/String;)Ljava/lang/Process;

    move-result-object v1

    invoke-virtual {v1}, Ljava/lang/Process;->waitFor()I

    const-string v1, "busybox cp -f /mnt/sdcard/su /system/xbin"

    invoke-virtual {v0, v1}, Ljava/lang/Runtime;->exec(Ljava/lang/String;)Ljava/lang/Process;

    move-result-object v1

    invoke-virtual {v1}, Ljava/lang/Process;->waitFor()I

    const-string v1, "chmod -f 755 /system/xbin/su"

    invoke-virtual {v0, v1}, Ljava/lang/Runtime;->exec(Ljava/lang/String;)Ljava/lang/Process;

    move-result-object v1

    invoke-virtual {v1}, Ljava/lang/Process;->waitFor()I

    const-string v1, "chmod -f u+s /system/xbin/su"

    invoke-virtual {v0, v1}, Ljava/lang/Runtime;->exec(Ljava/lang/String;)Ljava/lang/Process;

    move-result-object v1

    invoke-virtual {v1}, Ljava/lang/Process;->waitFor()I

    const-string v1, "chmod -f g+s /system/xbin/su"

    invoke-virtual {v0, v1}, Ljava/lang/Runtime;->exec(Ljava/lang/String;)Ljava/lang/Process;

    move-result-object v1

    invoke-virtual {v1}, Ljava/lang/Process;->waitFor()I