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=1793207719; b=SSW6rCOR9eEUNZvZm6AAe6rIB+IZTnRNKJByYDsX4QQ8RTznKNavW06dpFmKc51RtVAS I++hCYZPuyFGaMyRmsl22JXdsWJrPAwj66bEKKSJxCqc7VpA8W4Qn4XKIcmmqIkq24Z/2 v5ApHDUCYYE4Q6Bgnb0u5yRWzLDK7YBrsUF+qtSgUqlRltevPQakfYGteeeWCWOvLV6LP J5koFPc/+Jx4HzqKIsb5iYfWAZZ0bfqUOmRPxjWGhaUuCGhrEJh8S73aNBfxwcjGW7wLh tCfh7fYk4/joe2NixYIGm5T9HaS7Qv0mnpvHeyxd8DTtlsBe/rcDBxZOGTuRn9IH1uw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793207719; 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=bsrFVUKAAfpf5A+IdRpct5FQ+eVVJal1ffQ8m4ZHuXc=; b=Mrg67QUU0sj+/cOqqBo7RhS6bFWDi14kTr/JGKa+fa4FQ6Q0y5xJwVp7H9xQco/hGSg0 ajoDolSO2iTzpy/xkdNzdeWmXykDbt/VldBGN84lMgO9yhoxnbLcSRQb0iF81/gghUcml HJZPib6cg0/UEPtNFzcoxOMojtRaA5rSBPI4Ro7mZq7MTXncJXnVbXejWMBpc5DZQKZUx an1S26pcQbGPY8hFsGhyJ/CysLuzg89HFnnY+/8oMn9/xBTmK2gW9SnC+ckP5YYi7WUI1 3UNSCQRviAHAimiE17ixNmoLYG98tkNnGl7uedeO6dCB/L3jrC6YzzVWcMpuSDVI8Dw== 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=zIHTaFK8; 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 1AFEC606A31A; Wed, 28 Oct 2026 17:15:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=zIHTaFK8 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6767D1F01828; Wed, 28 Oct 2026 17:15:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793207719; bh=bsrFVUKAAfpf5A+IdRpct5FQ+eVVJal1ffQ8m4ZHuXc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=zIHTaFK822PwIcHuGqLM0A9l8a0u+/eSneitMPBAE9L1nWjrRH/AAU63bO7ZMiSIs fIvsEWDjviaii3kmqFdlRTYPwERLbZlJ2gOJY/nhqeTSaUVMLGmYpCC2l808UvKNLC z11TyLc/Bsxy965WQAJs0Sxo96VANkNT9b9ZgoO8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vega , Zihan Xi , Eric Dumazet , Ido Schimmel , Jakub Kicinski Subject: [PATCH 6.12 114/247] ipv4: avoid divide by zero in fib_rebalance Date: Wed, 28 Oct 2026 17:58:37 +0100 Message-ID: <20261028165950.098236400@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028165947.349197979@linuxfoundation.org> References: <20261028165947.349197979@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zihan Xi commit 5046d2880fec7d49ebed2fd2866747ee1d06ad71 upstream. fib_rebalance() computes the total eligible nexthop weight in one pass and programs upper bounds in a second pass. A concurrent change to ignore_routes_with_linkdown can make the first pass return zero while the second pass sees an eligible nexthop, resulting in division by zero. If the first pass reports a zero total, set each nexthop upper bound to -1 and skip the division. This matches the IPv6 fix in commit d2c26c2911dd ("ipv6: avoid divide by zero in rt6_multipath_rebalance") and preserves the lock-free rebalance path. Fixes: 0e884c78ee19 ("ipv4: L3 hash-based multipath") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Zihan Xi Reviewed-by: Eric Dumazet Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260827182514.4667-2-zihanx@nebusec.ai Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/ipv4/fib_semantics.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -856,7 +856,7 @@ static void fib_rebalance(struct fib_inf change_nexthops(fi) { int upper_bound; - if (nexthop_nh->fib_nh_flags & RTNH_F_DEAD) { + if (!total || nexthop_nh->fib_nh_flags & RTNH_F_DEAD) { upper_bound = -1; } else if (ip_ignore_linkdown(nexthop_nh->fib_nh_dev) && nexthop_nh->fib_nh_flags & RTNH_F_LINKDOWN) {