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[34.85.207.234]) by smtp.gmail.com with ESMTPSA id 00721157ae682-84c9fbfff73sm13956087b3.0.2026.08.22.11.50.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 22 Aug 2026 11:50:54 -0700 (PDT) Date: Sat, 22 Aug 2026 14:50:53 -0400 From: Willem de Bruijn To: Alice Mikityanska , Willem de Bruijn , David Ahern , Ido Schimmel , Jakub Kicinski , Paolo Abeni Cc: "David S. Miller" , Eric Dumazet , Simon Horman , Shuah Khan , Hannes Frederic Sowa , Vadim Fedorenko , netdev@vger.kernel.org, Alice Mikityanska Message-ID: In-Reply-To: <20260822115717.1161782-4-alice.kernel@fastmail.im> References: <20260822115717.1161782-1-alice.kernel@fastmail.im> <20260822115717.1161782-4-alice.kernel@fastmail.im> Subject: Re: [PATCH net v3 3/4] selftests: net: Test UDP length overflow with PMTU discover and big MTU Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Alice Mikityanska wrote: > From: Alice Mikityanska > > Two previous commits fixed overflow of UDP length when setsockopt > IP(V6)_MTU_DISCOVER is set to IPV6_PMTUDISC_DO or IP(V6)_PMTUDISC_PROBE, > and a large packet is sent over a netdev with an unusually large MTU. > > This commit adds the selftests that replicate the described steps to > reproduce for IPv6 and IPv4, and also one more test that ensures that > sending UDP jumbograms over a raw socket is still possible after the > fix. > > Signed-off-by: Alice Mikityanska > --- > tools/testing/selftests/net/Makefile | 1 + > tools/testing/selftests/net/cork_fragsize.py | 130 +++++++++++++++++++ > 2 files changed, 131 insertions(+) > create mode 100755 tools/testing/selftests/net/cork_fragsize.py > > diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile > index 0f5c178bc224..c6d332c90a54 100644 > --- a/tools/testing/selftests/net/Makefile > +++ b/tools/testing/selftests/net/Makefile > @@ -25,6 +25,7 @@ TEST_PROGS := \ > cmsg_so_mark.sh \ > cmsg_so_priority.sh \ > cmsg_time.sh \ > + cork_fragsize.py \ > double_udp_encap.sh \ > drop_monitor_tests.sh \ > ecmp_rehash.sh \ > diff --git a/tools/testing/selftests/net/cork_fragsize.py b/tools/testing/selftests/net/cork_fragsize.py > new file mode 100755 > index 000000000000..d89ef9892329 > --- /dev/null > +++ b/tools/testing/selftests/net/cork_fragsize.py > @@ -0,0 +1,130 @@ > +#!/usr/bin/env python3 > +# SPDX-License-Identifier: GPL-2.0 > + > +# Test possible UDP length overflow in udp_send_skb/udp_v6_send_skb. > + > +from lib.py import ksft_run, ksft_exit, ksft_true, KsftSkipEx > +from lib.py import ip, NetNS, NetNSEnter > +import errno > +import gzip > +import os > +import socket > +import struct > +import subprocess Various pylint and ruff issues, such as ordering imports > + > + > +IP_MTU_DISCOVER = 10 > +IP_PMTUDISC_PROBE = 3 > +IPV6_MTU_DISCOVER = 23 > +IPV6_PMTUDISC_DO = 2 > +IPV6_PMTUDISC_PROBE = 3 > +IPV6_TLV_JUMBO = 194 > + > + > +def check_kernel_config(option) -> bool | None: > + for filename, method in [ > + ('/proc/config.gz', gzip.open), > + (f'/boot/config-{os.uname().release}', open), > + ]: > + try: > + with method(filename, 'rt') as config: > + for line in config: > + if line.rstrip() == f'{option}=y': > + return True > + return False > + except OSError: > + continue > + > + > +def assert_debug_kernel() -> None: > + res = check_kernel_config('CONFIG_DEBUG_NET') > + if res is None: > + print("WARN: Can't read kernel config; assuming debug kernel, and running the test") > + elif not res: > + raise KsftSkipEx('CONFIG_DEBUG_NET is not set') > + > + > +def check_dmesg_clean(func) -> bool: > + dmesg = subprocess.Popen(['dmesg'], stdout=subprocess.PIPE) > + result = subprocess.run(['grep', '-q', f'WARNING:.*{func}'], stdin=dmesg.stdout) > + dmesg.wait() > + return result.returncode != 0 and dmesg.returncode == 0 > + > + > +def ip_setup(ns: NetNS, mtu: int, ipv6: bool) -> None: > + ip('link add dummy type dummy', ns=ns) > + ip(f'link set dummy mtu {mtu}', ns=ns) > + ip('link set dummy up', ns=ns) > + flag = '-6' if ipv6 else '' > + nodad = 'nodad' if ipv6 else '' > + addr_local = 'fd00::1/64' if ipv6 else '10.0.0.1/24' > + addr_remote = 'fd00::2' if ipv6 else '10.0.0.2' > + ip(f'{flag} addr add {addr_local} dev dummy {nodad}', ns=ns) > + ip(f'{flag} neigh add {addr_remote} lladdr 02:00:00:00:00:02 dev dummy nud permanent', ns=ns) > + > + > +def test_ipv6() -> None: > + assert_debug_kernel() > + > + with NetNS() as ns: > + ip_setup(ns, 65576, True) > + > + with NetNSEnter(ns): > + with socket.socket(socket.AF_INET6, socket.SOCK_DGRAM) as fd: > + fd.setsockopt(socket.IPPROTO_IPV6, IPV6_MTU_DISCOVER, IPV6_PMTUDISC_DO) > + try: > + fd.sendto(b' ' * 65528, ('fd00::2', 1234)) > + except OSError as e: > + # Ignore EMSGSIZE: it happens on kernels with the fix. > + if e.errno != errno.EMSGSIZE: > + raise > + > + ip('link del dummy', ns=ns) > + > + ksft_true(check_dmesg_clean('udp_v6_send_skb'), 'WARNING detected in dmesg') > + > + > +def test_ipv4() -> None: > + assert_debug_kernel() > + > + with NetNS() as ns: > + ip_setup(ns, 65556, False) > + > + with NetNSEnter(ns): > + with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as fd: > + fd.setsockopt(socket.IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_PROBE) > + try: > + fd.sendto(b' ' * 65528, ('10.0.0.2', 1234)) > + except OSError as e: > + # Ignore EMSGSIZE: the check happens after the WARN is printed. > + if e.errno != errno.EMSGSIZE: > + raise > + > + ip('link del dummy', ns=ns) > + > + ksft_true(check_dmesg_clean('udp_send_skb'), 'WARNING detected in dmesg') These two are identical apart from 7 constants. Dedup and use @ksft_variants decorators? > +def test_ipv6_jumbo() -> None: > + with NetNS() as ns: > + ip_setup(ns, 65584, True) > + > + with NetNSEnter(ns): > + with socket.socket(socket.AF_INET6, socket.SOCK_RAW, socket.IPPROTO_UDP) as fd: > + hopopts = struct.pack('!BBBBI', 0, 0, IPV6_TLV_JUMBO, 4, 65544) > + fd.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_HOPOPTS, hopopts) > + fd.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_CHECKSUM, 6) > + fd.setsockopt(socket.IPPROTO_IPV6, IPV6_MTU_DISCOVER, IPV6_PMTUDISC_PROBE) > + udp = struct.pack('!HHHH', 1234, 1234, 0, 0) + b' ' * 65528 > + fd.sendto(udp, ('fd00::2', 0)) > + > + ip('link del dummy', ns=ns) Should this have some test at the end? check_dmesg_clean or perhaps a socket receiving the data. > + > + > +if __name__ == "__main__": > + ksft_run([ > + test_ipv6, > + test_ipv4, > + test_ipv6_jumbo, > + ]) > + ksft_exit() > -- > 2.55.0 >