From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f176.google.com (mail-yw1-f176.google.com [209.85.128.176]) (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 26B2C233945 for ; Sat, 23 May 2026 17:23:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779557018; cv=none; b=oa+fRKslPSUYglazIJRuR3QJtWiyGSDT3G5BgHZUZisBWl4tfWc9H+D0PoZ+w3oEbGERsHCrFVGUJZQUB9/VLTzM0FY+ddCGbhxMLlA2GZGGVPVyVuzrvJXEhAxZnay5QkRJjHxY2AMFZTiMge4nbqgJvVm8MCSDLuLKYZFPL5U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779557018; c=relaxed/simple; bh=Fi4+ue6MQehKHGj6eR0P1A4AvxISsRbzoo/k8cV2AcM=; h=Date:From:To:Cc:Message-ID:In-Reply-To:References:Subject: Mime-Version:Content-Type; b=q2/oy4XJJKqbXoq6+Rr+BTnOV6WbaN6NGbdzKl/SK3ISCogZWGz/ci0LQOgQgXHbcckW3Z6dLS7P9JoSd2zcQnW5Bes6s4qdUxTqKJV2GqG6dFh79aCiDaywBP9yHJV0/dXbhHNCTVibdCCSi+07aT2Ny/kx1dOGTOY7gwCKMnw= 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=sMHogzmz; arc=none smtp.client-ip=209.85.128.176 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="sMHogzmz" Received: by mail-yw1-f176.google.com with SMTP id 00721157ae682-7b6ae2ea4a1so85448477b3.2 for ; Sat, 23 May 2026 10:23:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1779557016; x=1780161816; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=AH8I42OgtO38xei/x0QO150kONrNvsRLDU4qo5q/+2g=; b=sMHogzmzUJr8JJlpxA8s//WIx7vaBLTM9NzlUkjRZeUnKNhoTMpnOALbyta8inDD7+ Qxhtjuj+JBMMBcV1VWXPqbKfJqzKgNYSgIfvGpESFmDGvN8Pr3qgIQRFsy0gWAlO83aw UvSqezG/QoErvh125dEH22JycHa16nXHWtAW2PVGdQZuDQH8wElottWeXXqrGKKfgjM3 3Sm5euB5reTP3UkS0otK9/AKJAP7gYJUctyTS8bWytb+TA6rhHb5mRDqrsOCnTmiMtBb 884t+fsL7jJoP5ZK1W4LKu4/L5Sk3EYlN/14b+mDaA5VP46i1QoR8IXASlrgOUhjDmbq T6xQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779557016; x=1780161816; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:x-gm-gg:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=AH8I42OgtO38xei/x0QO150kONrNvsRLDU4qo5q/+2g=; b=fi8NJKOWNro6pbKRXJk5bZESkfOuqJxvQQmeJ9AiMdbkKzGeQ+8KBccINX/Gl0unlo jDMC3SYxg1jAYPAIs3O41xnlYKtC7InR5ClMmQaa3E2etblNkePmo2EzcycAIvrWA0Fh A6s2l8JIef/ZO2itad39naNGKDjvWqwyu+9okEX+s/YI7ZvWClbZTx0RvtY+nVBFMyUT k1g2DVG9YGxCXhxvB3XOmPXDhZGF0ngv5HAeKl7oaE1bQ/4u4axcc+evBjj3fdwclrRN KRxDFaPdj72ntugelVNHCUsD7qsTzD9G7hYKOOpKF7czC0j6Qj8HKPvZDTv0BnzkUzO0 nz8Q== X-Forwarded-Encrypted: i=1; AFNElJ9oVGTNZj1t4Q54oyM4z93NFqsSZGAUFw18tqm0DSBbFyDzJ58j09q4gBgPYdO64RlYhv/CkxwnALjlHT8=@vger.kernel.org X-Gm-Message-State: AOJu0YxiP+E46iOxF/zMHS2tfypAYaVKzyIb7no0LazwxZlWp/iFNx9g KvBy2KKPlZZyT4azrAxWO5/akyXMjXVC7d/U7AnVqWDwA1zYMCu8hPW7 X-Gm-Gg: Acq92OFsrbiJFzXVi9WVHbKMHGSBrh7TZ+8CAeP8yxKOc/oy6HOYBVaoC0pYJxatK4f R34SpTxRQA4nClGLNuDFw0Q/RdTjk85+e99be2zKWdCuVvlpa2bIKVsderumf244VuPeWnjVQxC DHIlSz/0lt2T0SlP+wznS46nC1FTLphjcL8hCfJkHMSO1Qjw/5CeFXLEPNHALpYxgGix0DMYTE+ a0l3veQACUu5HpmI5+1weMJmoSJbQARxTQCIJSaZr/XNxS7VrMdJLgwd6zsHIGhnnt8EpDwAgR7 ZUFZwHh0rPZNqZVUA9mSPj+iucX0a00X+YIyEPe6M0onAxk1Z9VNTi1hI58mN24c8Kcsc1neoWj S1fJJHv3c5HaLVvUygsQTHyZj/FnlX9T4rZlm9feYCTxNlAmgJMDjbFUaYQRp/fb/bMu4PcwEAL z8FuDFwpcYzBh8g5jAu11lNmu/+CKi3kfrednY1TxKy2tCRtfbV+dae6IzKSqDU7OyeKOtaRYmb Yk+CG/zOClXhbswIA== X-Received: by 2002:a05:690c:d1d:b0:7b4:dc3a:79c5 with SMTP id 00721157ae682-7d3340d954amr105142577b3.12.1779557016220; Sat, 23 May 2026 10:23:36 -0700 (PDT) Received: from gmail.com (141.139.145.34.bc.googleusercontent.com. [34.145.139.141]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7d389d17ffbsm23895387b3.14.2026.05.23.10.23.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 May 2026 10:23:35 -0700 (PDT) Date: Sat, 23 May 2026 13:23:34 -0400 From: Willem de Bruijn To: Qi Tang , davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, edumazet@google.com, David Ahern , Simon Horman Cc: willemdebruijn.kernel@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Qi Tang , stable@vger.kernel.org Message-ID: In-Reply-To: <20260523143245.2281415-1-tpluszz77@gmail.com> References: <20260523143245.2281415-1-tpluszz77@gmail.com> Subject: Re: [PATCH net v5] ipv6: validate extension header length before copying to cmsg 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: 7bit Qi Tang wrote: > ip6_datagram_recv_specific_ctl() builds IPV6_{HOPOPTS,DSTOPTS,RTHDR} > cmsgs (and their IPV6_2292* legacy counterparts) by trusting the > on-wire hdrlen byte (ptr[1]) when computing the put_cmsg() length. > The length was validated only at parse time (ipv6_parse_hopopts(), > etc.). An nftables payload-write expression can rewrite hdrlen after > parsing and before the skb reaches recvmsg; the write itself is > in-bounds but put_cmsg() then reads up to ((hdrlen+1) << 3) = 2040 > bytes from an 8-byte header. nftables is reachable from an > unprivileged user namespace, so this is an unprivileged > slab-out-of-bounds read: > > BUG: KASAN: slab-out-of-bounds in put_cmsg+0x3ac/0x540 > put_cmsg+0x3ac/0x540 > udpv6_recvmsg+0xca0/0x1250 > sock_recvmsg+0xdf/0x190 > ____sys_recvmsg+0x1b1/0x620 > > Add ipv6_get_exthdr_len() which validates that at least two bytes > are accessible before reading the hdrlen field, then checks the > computed length against skb_tail_pointer(skb), returning 0 on > failure. Extension headers are kept in the linear skb area by > pskb_may_pull() during input, so skb_tail_pointer() is the correct > bound. > > Use ipv6_get_exthdr_len() at all non-AH call sites: the five > standalone cmsg blocks (HbH, 2292HbH, 2292DSTOPTS x2, 2292RTHDR) > and the three standard cases in the extension-header walk loop > (DSTOPTS, ROUTING, default). AH retains an inline bounds check > because its length formula differs ((ptr[1]+2)<<2). > > The walk loop also gets a pre-read bounds check at the top to > validate ptr before any case accesses ptr[0] or ptr[1]. > > When the walk loop detects a corrupted header, return from the > function instead of continuing to process later socket options. > > Cc: stable@vger.kernel.org > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Signed-off-by: Qi Tang Reviewed-by: Willem de Bruijn > --- > Changes v4 -> v5 (Jakub Kicinski): > - Switch (ptr + len <= tail) to (len <= tail - ptr) form in > ipv6_get_exthdr_len() to avoid pointer arithmetic concerns. Please do send the net-next patch replacing the open constants with offsetof and such. > @@ -664,26 +679,37 @@ void ip6_datagram_recv_specific_ctl(struct sock *sk, struct msghdr *msg, > unsigned int len; > u8 *ptr = nh + off; > > + if (ptr + 2 > skb_tail_pointer(skb)) > + return; > + > switch (nexthdr) { > case IPPROTO_DSTOPTS: > nexthdr = ptr[0]; > - len = (ptr[1] + 1) << 3; > + len = ipv6_get_exthdr_len(skb, ptr); > + if (!len) > + return; > if (np->rxopt.bits.dstopts) > put_cmsg(msg, SOL_IPV6, IPV6_DSTOPTS, len, ptr); > break; > case IPPROTO_ROUTING: > nexthdr = ptr[0]; > - len = (ptr[1] + 1) << 3; > + len = ipv6_get_exthdr_len(skb, ptr); > + if (!len) > + return; Optional: instead of return, jump out of the while loop and continue processing other cmsg not based on exthdrs. > if (np->rxopt.bits.srcrt) > put_cmsg(msg, SOL_IPV6, IPV6_RTHDR, len, ptr); > break; > case IPPROTO_AH: > nexthdr = ptr[0]; > len = (ptr[1] + 2) << 2; > + if (ptr + len > skb_tail_pointer(skb)) > + return; > break; > default: > nexthdr = ptr[0]; > - len = (ptr[1] + 1) << 3; > + len = ipv6_get_exthdr_len(skb, ptr); > + if (!len) > + return; > break; > } >