rop.syscall attribute fails to find syscall gadget

[nbulischeck]

This line fails to find valid syscall gadgets. I'm not 100% sure if that for loop is a valid solution.

pwntools/pwnlib/rop/rop.py

Line 1276 in c15afc5

if self.gadgets[each]['insns'] == [mapping[attr]]:

>>> binary = ELF.from_assembly('syscall; ret')
>>> rop = ROP(binary)
>>> rop.syscall # No result
>>> [rop.gadgets[gadget] for gadget in rop.gadgets if 'syscall' in rop.gadgets[gadget]['insns']]
[Gadget(0x10000000, [u'syscall', u'ret'], [], 0x4)] # Syscall gadget

[saullocarvalho]

How can I help to fix this issue?
While reproducing the steps provided by @nbulischeck , I got the following:

>>> elf = ELF.from_assembly('syscall; ret')
>>> rop = ROP(elf)
>>> rop.syscall
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/hunter/app/pwntools/pwnlib/rop/rop.py", line 1398, in __getattr__
    if self.gadgets[each]['insns'] == [mapping[attr]]:
  File "/home/hunter/app/pwntools/pwnlib/rop/gadgets.py", line 57, in __getitem__
    if isinstance(key, six.integer_types):
NameError: name 'six' is not defined
>>> rop.gadgets.items()
dict_items([(268435458, Gadget(0x10000002, ['ret'], [], 0x4)), (268435456, Gadget(0x10000000, ['syscall'], [], 0x0))])

pwnlib/rop/gadgets.py is missing import six. This is easy to fix.

Regarding the original issue, should the syscall gadget have only the syscall instruction or should insns also include ret?

[saullocarvalho]

ROPgadget is returning the syscall gadget and the gadget does not follow the instructions until it reaches a ret. That seems odd to me.

[Arusekk]

Fixed in #1678 and #1682.