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=1793209565; b=0ZdTARGBuGhzm5qUCzjgyn03IkkTyfVZXEIbHYls0CuLXRnc0yw+9R0sDX5ZdSVK3KqJ /BpSP4OnVJsN3vyvEi22PlxwMp7AN7DCp/bwIW/VnLofMU855r5ru2D8suWxwbsibitYZ I2Vr1NA4LzYDYVrBA8H5mc746U6v4T4oLr5TLy3eFCAiyfRo+vdWLu1um5mChZw+f8kBs JuOtV7skS/g2hHO9KkZo2+5XFDPC6hZLwr9eqQR4/4b94tAdTcbGeYHbYXHZnEocZOLH+ iEj3KRuUMoOluINExaTspbm4wNfbvWECzJKxJHTEznk08Jgm9tK6iCma7ck1sT+T4lg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793209565; 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=tm9coUt8jdhNC0XwijNIYd+RPn1Y61U6hfbOzodh0Ss=; b=09etXaZg10EXNHIfCLxrEr4k18YXASRiPYeuaCg//rwUcKhyIQXWutww9ASppyLWqQTc B2LtzH9qGnzSsGqw1w5sI7FrTLRizGJut96GNw8Xx62HbA9kxeRLxXDgWbzTCMRjRq418 9rfR5M2ezF34IFlAqANSQXFHeoznfRx9WWOCWd+0r44FpEbedk408+Ye6GjsltzQuv59e tIOipDWcNHmD75WVbwn12hIoy0No71+inF/Ad5wu5lcXaiIsTNzf1Ox8l/qh5KppbhiQ8 wO3FnCsQxPEE+2GkDQP/vf1GNZY6apvW+fsFp92PRbu7hexeTgR02Ee6OLgc7/Z2x6A== 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=azqzJxzI; 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 955A3606A31D; Wed, 28 Oct 2026 17:46:05 +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=azqzJxzI Received: by smtp.kernel.org (Postfix) with ESMTPSA id E64131F01825; Wed, 28 Oct 2026 17:46:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793209565; bh=tm9coUt8jdhNC0XwijNIYd+RPn1Y61U6hfbOzodh0Ss=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=azqzJxzIN9Vd2+LcRlDf3p007sTsGQ0VBix8r7wuiCQNkNVjmcCFuoPhLfT4l5LZZ QO/9RwqvXLSisTPW1ekC0VsG8tUdqW+cc4ZPGrsv5KOUGWJlvzumCB0QVVuCe67Txt FeW7no87ulrOMs6VtgtHPcPKCzYCvHVFLBMZ8YXY= 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 5.10 473/516] ipv4: avoid divide by zero in fib_rebalance Date: Wed, 28 Oct 2026 18:00:25 +0100 Message-ID: <20261028170014.687165675@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170003.522232767@linuxfoundation.org> References: <20261028170003.522232767@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 5.10-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 @@ -851,7 +851,7 @@ 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) {