From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 352CC2D5940; Wed, 28 Jan 2026 15:35:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769614549; cv=none; b=IsDExXB8Q3qe9PrQQ+tGQ8/JEfw3kdy9zicTcTUcSXP6i2Rd0UXz2OxSsYmkNzGFbseaSslxwQmZs/ko7z/nfNx4MGwtXvWMkp0f8czuf5SpU4X1wcEVWscw0zmQ6N9U/ZbkZwc1yAub5EzubDQqSYUvl7EnLN2fpi3O1bsTWfA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769614549; c=relaxed/simple; bh=r8qDmTCx96EDDL4kdo7SPIvg/BcldeBD81fFXCj1iKk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=owxtTbac0j/SkfFumog1dRdFCwetanim7sxbxThB+za26JYIkVtAcs8JomQSH50uHT/XyvqtV847EOTRz1Jieo01Ea1TK1dlYJDRdqm6zgTZSFHPuOCALAk5iM0qHI7U2je3LnTLvcC3A1pEw7+DMrGIyVHI6h8AsUiSgCOoEDk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=BDSossXB; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="BDSossXB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5D132C4CEF1; Wed, 28 Jan 2026 15:35:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1769614548; bh=r8qDmTCx96EDDL4kdo7SPIvg/BcldeBD81fFXCj1iKk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BDSossXB0b/z/hphYmUjY6qIh977cjWDuTNQgI3UmN/DnDJUeme96OHC6JeqIp0sO OH/cC+N+DXFD++P0qQ4TKuc01bAszZo122hkhWezIJCjQXCUSLgwML9nOp9HK5AIlW 31G4BcNSR+PW39/9VtPrQDauQnsTXJ2UgwxwX0so= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot , Eric Dumazet , Rocco Yue , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.6 169/254] ipv6: annotate data-race in ndisc_router_discovery() Date: Wed, 28 Jan 2026 16:22:25 +0100 Message-ID: <20260128145350.888965176@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260128145344.698118637@linuxfoundation.org> References: <20260128145344.698118637@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit 9a063f96d87efc3a6cc667f8de096a3d38d74bb5 ] syzbot found that ndisc_router_discovery() could read and write in6_dev->ra_mtu without holding a lock [1] This looks fine, IFLA_INET6_RA_MTU is best effort. Add READ_ONCE()/WRITE_ONCE() to document the race. Note that we might also reject illegal MTU values (mtu < IPV6_MIN_MTU || mtu > skb->dev->mtu) in a future patch. [1] BUG: KCSAN: data-race in ndisc_router_discovery / ndisc_router_discovery read to 0xffff888119809c20 of 4 bytes by task 25817 on cpu 1: ndisc_router_discovery+0x151d/0x1c90 net/ipv6/ndisc.c:1558 ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841 icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989 ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438 ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489 NF_HOOK include/linux/netfilter.h:318 [inline] ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500 ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590 dst_input include/net/dst.h:474 [inline] ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79 ... write to 0xffff888119809c20 of 4 bytes by task 25816 on cpu 0: ndisc_router_discovery+0x155a/0x1c90 net/ipv6/ndisc.c:1559 ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841 icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989 ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438 ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489 NF_HOOK include/linux/netfilter.h:318 [inline] ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500 ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590 dst_input include/net/dst.h:474 [inline] ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79 ... value changed: 0x00000000 -> 0xe5400659 Fixes: 49b99da2c9ce ("ipv6: add IFLA_INET6_RA_MTU to expose mtu value") Reported-by: syzbot Signed-off-by: Eric Dumazet Cc: Rocco Yue Link: https://patch.msgid.link/20260118152941.2563857-1-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv6/ndisc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c index d8e5e2833eded..80ceb401ecf2d 100644 --- a/net/ipv6/ndisc.c +++ b/net/ipv6/ndisc.c @@ -1574,8 +1574,8 @@ static enum skb_drop_reason ndisc_router_discovery(struct sk_buff *skb) memcpy(&n, ((u8 *)(ndopts.nd_opts_mtu+1))+2, sizeof(mtu)); mtu = ntohl(n); - if (in6_dev->ra_mtu != mtu) { - in6_dev->ra_mtu = mtu; + if (READ_ONCE(in6_dev->ra_mtu) != mtu) { + WRITE_ONCE(in6_dev->ra_mtu, mtu); send_ifinfo_notify = true; } -- 2.51.0