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DARWIN/MacOS patch to fix word alignment of netmask in sockaddr.sa_data and filter ARP entries #4895

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DARWIN/MacOS patch to fix word alignment of netmask in sockaddr.sa_data and filter ARP entries #4895

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a69e067
DARWIN/MacOS patch to fix:
jhogg Jan 5, 2026
20fc67a
Further review of DARWIN indicates the address structures (including …
jhogg Jan 6, 2026
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27 changes: 21 additions & 6 deletions scapy/arch/bpf/pfroute.py
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Original file line number Diff line number Diff line change
Expand Up @@ -401,12 +401,23 @@ class sockaddr(Packet):
XStrLenField("sdl_pad", b"", length_from=lambda pkt: 16 - pkt.sa_len),
lambda pkt: pkt.sa_len < 16 and pkt.sa_family == socket.AF_LINK,
),
# others
# others - only used for netmask, make alignment match sockaddr_in
ConditionalField(
StrFixedLenField("_sa_pad1", "", 2),
lambda pkt: pkt.sa_family
not in [
socket.AF_INET,
socket.AF_INET6,
socket.AF_LINK,
],
),
ConditionalField(
XStrLenField(
"sa_data",
"",
length_from=lambda pkt: pkt.sa_len - 2 if pkt.sa_len >= 2 else 0,
# NOTE: Adjust length to 4 byte alignment. Darwin sa_len is not always correct for simple math.
length_from=lambda pkt:
((pkt.sa_len+3)//4*4 - 4 if pkt.sa_len >= 2 else 0)
),
lambda pkt: pkt.sa_family
not in [
Expand Down Expand Up @@ -1020,9 +1031,13 @@ def read_routes():
flags = msg.rtm_flags
if not flags.RTF_UP:
continue
if DARWIN and flags.RTF_WASCLONED and msg.rtm_parentflags.RTF_PRCLONING:
# OSX needs filtering
continue
if DARWIN:
if flags.RTF_WASCLONED and msg.rtm_parentflags.RTF_PRCLONING:
# OSX needs filtering
continue
if flags.RTF_HOST and not flags.RTF_BROADCAST:
# DARWIN includes the entire ARP table in the route response. Remove it.
continue
addrs = msg.rtm_addrs
net = 0
mask = 0xFFFFFFFF
Expand All @@ -1046,7 +1061,7 @@ def read_routes():
if nm.sa_family == socket.AF_INET:
mask = atol(nm.sin_addr)
elif nm.sa_family in [0x00, 0xFF]: # NetBSD
mask = struct.unpack("<I", nm.sa_data[:4].rjust(4, b"\x00"))[0]
mask = struct.unpack(">I", nm.sa_data[:4].rjust(4, b"\x00"))[0]
else:
mask = int.from_bytes(nm.sa_data[:4], "big")
i += 1
Expand Down