From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794590100; b=1Rb6kDpIRSeUDhtXPwITAChB9Tq0U1DXSkQwy/1YyodH9NfOyO5h0Jk+dFxgYau89SVK dxL6yfSRlPJBTM7aW6J+cg6PLgLKGhfj2I64Ch/uAOq0FITYiBMHmaeBCdDFgBE5VEWuZ 99lCOdGTod8yCG22InvU3vHpiYpVQjrLdRFHE+hQLh0JKHVBKtO3ZEZbYGpfPM0POFZda zx0wH/sTJZC3y6OHRZAxrvoXX3cydxp5+wFeelvjRcG/+hhOSG9DsHIcYBtsodJYDw1jH 4zuOza4kKMvm2T4LJoyqt2zFGZh0VLGuqac5MZBbjKd5il2SO/lal71XUryL8375IEQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794590100; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=keye52/HrAEr6dWGrZ/WItjb9rOtl48+5N+EwX1fC/Y=; b=EaL6WRAu0s5hS6X1CAPCtCnTLq2mvpr6kgSRcwP8g0g9Y505tFUgFK8g4n9jozd7EwLV 8Xk8su70ROiLn1aje/v43gk9qnqLnP1wG42gt+D/tLrJHXis5kePpwQBn8UI9SRSfjrZo DK4+5CThw5WsZ8SuJoiZD2ICzC15VagebdJpRRybwjdfTApsKA4ODTmPuZW2DxggB2MJe +cUYYFu8ZkzrTmPLXkG07epytgTwO7CT9boY6j8xqbQGuP9eAbposokxPd3ULK34V5RHp Sb95hyAeh08wjFf4+30qoUwlsn535JnIZnNTow5row2GFXMigys/b6zxHZV0ZpAAHzg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=Nwn+aIKM; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B776E60A262A; Fri, 13 Nov 2026 17:15:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=Nwn+aIKM Received: by smtp.kernel.org (Postfix) with ESMTPSA id 72D921F000C5; Fri, 13 Nov 2026 17:15:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794590100; bh=keye52/HrAEr6dWGrZ/WItjb9rOtl48+5N+EwX1fC/Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Nwn+aIKMUegSW7qz2OWpnW9KKwwpLe2wxXTyGH4L6ROAK7o+hJzj1rkybwY7UH5MS 12t+Og8yUhoWSnsDq7TIvYc7SWoAuGhnTh+YeaKlhDGwJ+UENyHYgrD/+GxjPZ4KUm 71kDNK4r8Osy0KUyV0Ar51rhL19NIGOlR9fTZEls= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Bernard Pidoux , Sasha Levin Subject: [PATCH 6.18 124/686] ax25: keep the window below 8 when a socket goes back to modulo 8 Date: Fri, 13 Nov 2026 10:44:17 -0500 Message-ID: <20261113153825.024332727@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153820.902362109@linuxfoundation.org> References: <20261113153820.902362109@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Bernard Pidoux AX25_WINDOW accepts 1 to 63 on a socket in extended mode, but AX25_EXTSEQ set back to 0 leaves the window as it was. With modulo 8, ax25_kick() computes the end of the window as (V(A) + window) % 8: a window of 8, 16, ... 56 gives V(A) itself, the window looks full, and the connection never sends an I frame. Other values wrap round to a smaller window. Bring the window down to 7 when AX25_EXTSEQ selects modulo 8. Tested on a QEMU bench (6.12.94 with KASAN and lockdep, two guests over a KISS serial link). B sets AX25_EXTSEQ 1, AX25_WINDOW 16, AX25_EXTSEQ 0, calls A with a SABM and sends 5 messages: before: window read back 16, A receives none of the 5 messages after: window read back 7, A receives the 5 messages Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Bernard Pidoux Assisted-by: Claude:claude-opus-5-5 (cherry picked from commit bcd2f2d49b5af392504f29292cbd622d857507b6) Signed-off-by: Sasha Levin --- net/ax25/af_ax25.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c index e1a47489c601f..81616e8438ce4 100644 --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -708,6 +708,12 @@ static int ax25_setsockopt(struct socket *sock, int level, int optname, case AX25_EXTSEQ: ax25->modulus = opt ? AX25_EMODULUS : AX25_MODULUS; + /* + * A window set for modulo 128 may not fit modulo 8: + * ax25_kick() would then find it full and send nothing. + */ + if (ax25->modulus == AX25_MODULUS && ax25->window > 7) + ax25->window = 7; break; case AX25_PIDINCL: -- 2.53.0