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From: Qingfang Deng <qingfang.deng@linux.dev>
To: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Simon Horman <horms@kernel.org>, Shuah Khan <shuah@kernel.org>,
	Qingfang Deng <qingfang.deng@linux.dev>,
	linux-ppp@vger.kernel.org, netdev@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Matthieu Baerts <matttbe@kernel.org>
Subject: [PATCH net-next] selftests: net: do not detect PPPoX loopback
Date: Wed,  3 Jun 2026 14:17:44 +0800	[thread overview]
Message-ID: <20260603061746.23452-1-qingfang.deng@linux.dev> (raw)

By default, pppd attempts to detect loopbacks on the underlying
interface using a pseudo-randomly generated magic number and checks if
the same value is received. The seed for the PRNG is a hash of hostname
XOR current time XOR pid, which is likely to collide on NIPA, causing
false positives. Disable magic number generation.

Reported-by: Matthieu Baerts <matttbe@kernel.org>
Fixes: 7af2a94f4dcf ("selftests: net: add tests for PPPoL2TP")
Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
---
 tools/testing/selftests/net/ppp/pppoe-server-options | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/net/ppp/pppoe-server-options b/tools/testing/selftests/net/ppp/pppoe-server-options
index 66c8c9d319e9..cd586be7061b 100644
--- a/tools/testing/selftests/net/ppp/pppoe-server-options
+++ b/tools/testing/selftests/net/ppp/pppoe-server-options
@@ -1,2 +1,3 @@
 noauth
 noipdefault
+nomagic
-- 
2.43.0


             reply	other threads:[~2026-06-03  6:18 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-06-03  6:17 Qingfang Deng [this message]
2026-06-06  0:40 ` [PATCH net-next] selftests: net: do not detect PPPoX loopback patchwork-bot+netdevbpf

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