From nobody Thu Apr 2 18:51:23 2026 Received: from mail-pl1-f178.google.com (mail-pl1-f178.google.com [209.85.214.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C5EAF249E5 for ; Fri, 27 Mar 2026 02:25:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.178 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774578315; cv=none; b=KUoL41/msvGMUCKS3C5pYbJ1xkIOCYR2g36ZCg2OO+B17pL1EkcgYrfIUcb/XeCgyCKWv1aVOr0db5JI7JVKUb75LR9zJBpiZuSRjYlxuc5J/hEMvgD7eg/Kqg58P8QenVHhUi3dny2yynNdjOrbCQAh3tJBqLhIpnlDCfzWO7M= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774578315; c=relaxed/simple; bh=GA9iJ3FHlrroqC2NNiJuu9RWhIYVniR+DEyF4ubqR/A=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=TEmU03K4v6zaUsfchmfhlSAMcCYYqL4A/yrKwavYJoaCA+Kl9x3NmXb6G3hul8z598Kz5ZUqQf0nnj8iuNY7BoluNTd7Tr52doGvY2BHxP0cukJ2eucL1Y8wnzGKOA3yLFZMEE6i3a1kgxffJX4cw1SRSbyuf+QEXf7hj/VCVlE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=MeZCcFZK; arc=none smtp.client-ip=209.85.214.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="MeZCcFZK" Received: by mail-pl1-f178.google.com with SMTP id d9443c01a7336-2b0c30b517aso5207065ad.3 for ; Thu, 26 Mar 2026 19:25:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1774578313; x=1775183113; darn=vger.kernel.org; h=cc:to:message-id:content-transfer-encoding:mime-version:subject :date:from:from:to:cc:subject:date:message-id:reply-to; bh=RgsriYW27LYcQzITLoiIl7pLc3IW/A/busdV44W1OJw=; b=MeZCcFZKlwi3rNFgQ5ayoTF+0SnE7Ehttu0O1M+2/9F5Tu20xyHa1GE/UhOsEDS5mi lUPW43+a68DUvrg3Vv2j2p5CHU5u355wz1D78QYuMlc4kRi93Fzd2Bafpvq5/rlzTNRP hGlGkFBGX6di/8lG+Kd7JYbySnIAz6ygRhpOnO9xrI5DjjXLsKuX39AYaUK/1xGRbQEW tYEZD8L0CoKL6HGM6EYsQ7a6weLcU4iTpsk0M+zuWH8VLterGLgISHGyN/tg+56NZaCM Bxr5e6IoAIGx6wbWNN48X7AfIQhqmgCtYSD31cZL6t/oFY1qJqFPW9DgNGSJCBrnX6k9 LMTw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774578313; x=1775183113; h=cc:to:message-id:content-transfer-encoding:mime-version:subject :date:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=RgsriYW27LYcQzITLoiIl7pLc3IW/A/busdV44W1OJw=; b=bqz4Pqj4FglK+7UUsSV/CbS2d3q7+UFIO4JhznlBM9UJ9Eki2kLQPd5HR6YQ2DZZt5 LeJUUmQ8AWCEEZWCGUi8kHhW3ysO6M8PfxtEogBhJG9Kyg4K5dK0ZHskyis7i9DVRuFl Wda1CnbXWojPcghvsOPQcib23Sf3IBd5E6p0sHCGTeHv27JDjQw9kuwLeu0wTjG2ELJH wKgBoZmxtu2tUnq87Qv8ISqz2yINuYFZUmIL1KtqE8twYoKFOotRKtbBHyvkpunPBbnS iFJFNU2K7Apm1pr2st0ZSc5gj9/Ysj2c6G3KrfSZ9Ff56WykGXZaANJo7xQdLKvs1afU OOag== X-Forwarded-Encrypted: i=1; AJvYcCWfvMH1hTnKKaax6Sg8xm2TFc9udpAaBmPpvNxDmeUFgJLgZUsRIGkbZSPkAAqAJxNbRWySDTPSvbH8tuM=@vger.kernel.org X-Gm-Message-State: AOJu0YxcH0pddtxiprP7Gl9m6MKCAjfHs+0Ks1UdyYjhC1chxBDnPWvJ DLCsZL2DwkkMCdEQew+0DtBYIxqox7eTJdRGBJW2vTT2RazWMxaXF/EV X-Gm-Gg: ATEYQzxBXa8EkI/truzEnMURQowJrbaJ0et5txg4FcyioccXOHM2WpZfv2+NIvYoOB9 ZtdWbxz+/Kic+yt70ClGwz2d4SEEFH2C5y+P3K9WvcCzcelG8uu0YzA6Ml8Kmz8dmp02uoTLT0m oIhrvRw+p45FW3hL44W+PdKwusJ6uzMGWOvRTMgGM6k4CMSuuTTb6LxvRzt2QQ9AAp+TIFh6J3T SE1UxuuUIBRVuyMsA/TxBQpX3fL26E6F6YFrpOE+WImpBAJAqqCrMCvngKX5wnOKXDbWWTrZUF9 NWQ8BiM1DkhC5fBiyjkjpJ+NX5Zs/jKm9Tj0pHA9zGsFDdMk+YHLqmgDYw+ekEoNy9XVO3dTMvX iYMzoZAc75tSliQe9ru2CQJQyf1YNRhGeawCTyWJ3zd/lQ0Vqxb1X6+tePss2RJDtmpakVDESy0 kKfmDWje7LnMJ/y8WAwlB8lVCbQbCqImc/+0Qq3yJU4ZRPXzANXfc75lqjfVn/OJQnPBozCNSup HwL+9rTXBihgUEbCPkp8AYGJCwgvTWifo3qiBWgOAzicrWlnpkZ X-Received: by 2002:a17:903:37ce:b0:2b0:41bf:ca83 with SMTP id d9443c01a7336-2b0cdcc8106mr9033135ad.23.1774578312983; Thu, 26 Mar 2026 19:25:12 -0700 (PDT) Received: from 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa ([240e:34c:576a:8120:d1e2:12aa:7df5:2768]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b0cb9ad55csm9423815ad.53.2026.03.26.19.25.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2026 19:25:12 -0700 (PDT) From: Hangbin Liu Date: Fri, 27 Mar 2026 10:24:47 +0800 Subject: [PATCH net v2] ipv6: fix data race in fib6_metric_set() using cmpxchg Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260327-b4-fib6_metric_set-kmemleak-v2-1-366b2c78b5c2@gmail.com> X-B4-Tracking: v=1; b=H4sIAAAAAAAC/42NWwqDMBBFtyLz3SkmWh/96j6KSJKOOmi0JEFax L03ZAX9POfCuQd4ckwe7tkBjnb2vK0R5CUDM6l1JORXZJC5rPJCVqhLHFhXvaXg2PSeAs6W7EJ qxlqpm2jrRjalglh4Oxr4k+pPWClAF+XEPmzumx53kaa/4rtAgaZpByN0IaTJH6NVvFzNZqE7z /MHHYTQ6csAAAA= X-Change-ID: 20260326-b4-fib6_metric_set-kmemleak-7aa51978284a To: "David S. Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jiayuan Chen Cc: David Ahern , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Fei Liu , Hangbin Liu X-Mailer: b4 0.14.3 fib6_metric_set() may be called concurrently from softirq context without holding the FIB table lock. A typical path is: ndisc_router_discovery() spin_unlock_bh(&table->tb6_lock) <- lock released fib6_metric_set(rt, RTAX_HOPLIMIT, ...) <- lockless call When two CPUs process Router Advertisement packets for the same router simultaneously, they can both arrive at fib6_metric_set() with the same fib6_info pointer whose fib6_metrics still points to dst_default_metrics. if (f6i->fib6_metrics =3D=3D &dst_default_metrics) { /* both CPUs: true= */ struct dst_metrics *p =3D kzalloc_obj(*p, GFP_ATOMIC); refcount_set(&p->refcnt, 1); f6i->fib6_metrics =3D p; /* CPU1 overwrites CPU0's p -> p0 leaked */ } The dst_metrics allocated by the losing CPU has refcnt=3D1 but no pointer to it anywhere in memory, producing a kmemleak report: unreferenced object 0xff1100025aca1400 (size 96): comm "softirq", pid 0, jiffies 4299271239 backtrace: kmalloc_trace+0x28a/0x380 fib6_metric_set+0xcd/0x180 ndisc_router_discovery+0x12dc/0x24b0 icmpv6_rcv+0xc16/0x1360 Fix this by: - Set val for p->metrics before published via cmpxchg() so the metrics value is ready before the pointer becomes visible to other CPUs. - Replace the plain pointer store with cmpxchg() and free the allocation safely when competition failed. - Add READ_ONCE()/WRITE_ONCE() for metrics[] setting in the non-default metrics path to prevent compiler-based data races. Fixes: d4ead6b34b67 ("net/ipv6: move metrics from dst to rt6_info") Reported-by: Fei Liu Signed-off-by: Hangbin Liu Reviewed-by: Jiayuan Chen --- Changes in v2: - Set val for p->metrics before published via cmpxchg() (Eric Dumazet) - Add READ_ONCE()/WRITE_ONCE() for metrics[] setting (Jiayuan Chen) - Link to v1: https://lore.kernel.org/r/20260326-b4-fib6_metric_set-kmemlea= k-v1-1-c89fc1b312c0@gmail.com --- net/ipv6/ip6_fib.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index dd26657b6a4a..2a7cc33fbcef 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -730,17 +730,24 @@ void fib6_metric_set(struct fib6_info *f6i, int metri= c, u32 val) if (!f6i) return; =20 - if (f6i->fib6_metrics =3D=3D &dst_default_metrics) { + if (READ_ONCE(f6i->fib6_metrics) =3D=3D &dst_default_metrics) { + struct dst_metrics *dflt =3D (struct dst_metrics *)&dst_default_metrics; struct dst_metrics *p =3D kzalloc_obj(*p, GFP_ATOMIC); =20 if (!p) return; =20 + p->metrics[metric - 1] =3D val; refcount_set(&p->refcnt, 1); - f6i->fib6_metrics =3D p; + if (cmpxchg(&f6i->fib6_metrics, dflt, p) !=3D dflt) + kfree(p); + else + return; } =20 - f6i->fib6_metrics->metrics[metric - 1] =3D val; + struct dst_metrics *m =3D READ_ONCE(f6i->fib6_metrics); + + WRITE_ONCE(m->metrics[metric - 1], val); } =20 /* --- base-commit: c4ea7d8907cf72b259bf70bd8c2e791e1c4ff70f change-id: 20260326-b4-fib6_metric_set-kmemleak-7aa51978284a Best regards, --=20 Hangbin Liu