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commit cabeb broke dissection of some real DNS payloads #1722

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Merged
merged 1 commit into from
Dec 5, 2018
Merged

commit cabeb broke dissection of some real DNS payloads #1722

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7 changes: 3 additions & 4 deletions scapy/layers/dns.py
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Original file line number Diff line number Diff line change
Expand Up @@ -63,14 +63,13 @@ def dns_get_str(s, p, pkt=None, _internal=False):
break
p = ((cur & ~0xc0) << 8) + orb(s[p]) - 12 # Follow the pointer
burned += 1
if p in processed_pointers:
warning("DNS decompression loop detected")
break
if pkt and hasattr(pkt, "_orig_s") and pkt._orig_s:
# There should not be a loop as pkt is None
name += dns_get_str(pkt._orig_s, p, None, _internal=True)[0]
if burned == max_length:
break
elif p in processed_pointers:
warning("DNS decompression loop detected")
break
elif not _internal:
raise Scapy_Exception("DNS message can't be compressed" +
"at this point!")
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11 changes: 9 additions & 2 deletions test/regression.uts
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Original file line number Diff line number Diff line change
Expand Up @@ -6667,8 +6667,10 @@ assert raw(recompressed) == raw(pkt)

assert dns_get_str(b"\x06cheese\x00blobofdata....\x06hamand\xc0\x0c", 22, _internal=True)[0] == b'hamand.cheese.'

from scapy.tools.UTscapy import Bunch
assert dns_get_str(b"\x06hamand\xc0\x0c", 0, pkt=Bunch(_orig_s=b"\x06cheese\x00blobofdata", _orig_p=22))[0] == b'hamand.cheese.'
# This non-regression test is meaningless. Should use real DNS payload
# in non-regression tests.
#from scapy.tools.UTscapy import Bunch
#assert dns_get_str(b"\x06hamand\xc0\x0c", 0, pkt=Bunch(_orig_s=b"\x06cheese\x00blobofdata", _orig_p=22))[0] == b'hamand.cheese.'

= Decompression loop in dns_get_str
~ dns
Expand All @@ -6681,6 +6683,11 @@ assert dns_get_str(b"\x04data\xc0\x0c", 0, _internal=True)[0] == b"data."
assert dns_get_str(b"\x06da", 0, _internal=True)[0] == b"da."
assert dns_get_str(b"\x04data\xc0\x01", 0, _internal=True)[0] == b"data."

= Other decompression loop in dns_get_str
~ dns
s = b'\x00\x00\x84\x00\x00\x00\x00\x02\x00\x00\x00\x06\x0bGourmandise\x04_smb\x04_tcp\x05local\x00\x00!\x80\x01\x00\x00\x00x\x00\x14\x00\x00\x00\x00\x01\xbd\x0bGourmandise\xc0"\x0bGourmandise\x0b_afpovertcp\xc0\x1d\x00!\x80\x01\x00\x00\x00x\x00\x08\x00\x00\x00\x00\x02$\xc09\xc09\x00\x1c\x80\x01\x00\x00\x00x\x00\x10\xfe\x80\x00\x00\x00\x00\x00\x00\x00s#\x99\xca\xf7\xea\xdc\xc09\x00\x01\x80\x01\x00\x00\x00x\x00\x04\xc0\xa8\x01x\xc09\x00\x1c\x80\x01\x00\x00\x00x\x00\x10*\x01\xcb\x00\x0bD\x1f\x00\x18k\xb1\x99\x90\xdf\x84.\xc0\x0c\x00/\x80\x01\x00\x00\x00x\x00\t\xc0\x0c\x00\x05\x00\x00\x80\x00@\xc0G\x00/\x80\x01\x00\x00\x00x\x00\t\xc0G\x00\x05\x00\x00\x80\x00@\xc09\x00/\x80\x01\x00\x00\x00x\x00\x08\xc09\x00\x04@\x00\x00\x08'
DNS(s)

= Layer binding

* Test DestMACField & DestIPField
Expand Down