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 5EAE1B67E; Wed, 8 Apr 2026 18:16:51 +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=1775672211; cv=none; b=oFJqrvZnCN6JEIevTP7dtarjuXtl0TRR3tdLJt/oQe6bDQ9loNBPPeN5X41Zbxw6vJz+5C9b1aNpCh8Ol5QYkSRyU4TVjPeJMRX+a/Ng3WvtcnWtrqLhLHLgsF9orBq64H/PD1nk/9qgTB2TcXtxG7nsttgm64dzCr030XXDzBg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775672211; c=relaxed/simple; bh=824t301g9+NRYF66bVo5iZw9zrQeoXviM3L2fH+9Eck=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OYMV9Qj2p/mIZl7wM5l4/6oWTRL2xZQayQKIGM4v9Z9fdJsR6A1kREsI+7gHBkgD88HL+0fbwh71jlV+OgrP8DpK3kr8hkwYnh28LfH9S8++fUiqMSH3AancF5yVwrL50rGdId8tpevYWx40tFE5cKNWfGCJqEyL/Gnm+A1fcWI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=v4bQXkTM; 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="v4bQXkTM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD43AC19421; Wed, 8 Apr 2026 18:16:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1775672211; bh=824t301g9+NRYF66bVo5iZw9zrQeoXviM3L2fH+9Eck=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=v4bQXkTMXC+yorD+jm2RiXz65fpVRbH4ziWM3hpZu6vNt0m3MVjrMVYLZtT5E55wB 3u3KkQRI1XChg9pdwU0E6G0IEiDbQPToh784WgKiEgKPZ60uqdMwSsaZjeF+2N7YoV IPaM89Zl5bN/hGWKL2qAU33Hm7tUNDkImJoj/FBU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yiming Qian , Eric Dumazet , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.1 190/312] ipv6: avoid overflows in ip6_datagram_send_ctl() Date: Wed, 8 Apr 2026 20:01:47 +0200 Message-ID: <20260408175940.856223889@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260408175933.715315542@linuxfoundation.org> References: <20260408175933.715315542@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 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit 4e453375561fc60820e6b9d8ebeb6b3ee177d42e ] Yiming Qian reported : I believe I found a locally triggerable kernel bug in the IPv6 sendmsg ancillary-data path that can panic the kernel via `skb_under_panic()` (local DoS). The core issue is a mismatch between: - a 16-bit length accumulator (`struct ipv6_txoptions::opt_flen`, type `__u16`) and - a pointer to the *last* provided destination-options header (`opt->dst1opt`) when multiple `IPV6_DSTOPTS` control messages (cmsgs) are provided. - `include/net/ipv6.h`: - `struct ipv6_txoptions::opt_flen` is `__u16` (wrap possible). (lines 291-307, especially 298) - `net/ipv6/datagram.c:ip6_datagram_send_ctl()`: - Accepts repeated `IPV6_DSTOPTS` and accumulates into `opt_flen` without rejecting duplicates. (lines 909-933) - `net/ipv6/ip6_output.c:__ip6_append_data()`: - Uses `opt->opt_flen + opt->opt_nflen` to compute header sizes/headroom decisions. (lines 1448-1466, especially 1463-1465) - `net/ipv6/ip6_output.c:__ip6_make_skb()`: - Calls `ipv6_push_frag_opts()` if `opt->opt_flen` is non-zero. (lines 1930-1934) - `net/ipv6/exthdrs.c:ipv6_push_frag_opts()` / `ipv6_push_exthdr()`: - Push size comes from `ipv6_optlen(opt->dst1opt)` (based on the pointed-to header). (lines 1179-1185 and 1206-1211) 1. `opt_flen` is a 16-bit accumulator: - `include/net/ipv6.h:298` defines `__u16 opt_flen; /* after fragment hdr */`. 2. `ip6_datagram_send_ctl()` accepts *repeated* `IPV6_DSTOPTS` cmsgs and increments `opt_flen` each time: - In `net/ipv6/datagram.c:909-933`, for `IPV6_DSTOPTS`: - It computes `len = ((hdr->hdrlen + 1) << 3);` - It checks `CAP_NET_RAW` using `ns_capable(net->user_ns, CAP_NET_RAW)`. (line 922) - Then it does: - `opt->opt_flen += len;` (line 927) - `opt->dst1opt = hdr;` (line 928) There is no duplicate rejection here (unlike the legacy `IPV6_2292DSTOPTS` path which rejects duplicates at `net/ipv6/datagram.c:901-904`). If enough large `IPV6_DSTOPTS` cmsgs are provided, `opt_flen` wraps while `dst1opt` still points to a large (2048-byte) destination-options header. In the attached PoC (`poc.c`): - 32 cmsgs with `hdrlen=255` => `len = (255+1)*8 = 2048` - 1 cmsg with `hdrlen=0` => `len = 8` - Total increment: `32*2048 + 8 = 65544`, so `(__u16)opt_flen == 8` - The last cmsg is 2048 bytes, so `dst1opt` points to a 2048-byte header. 3. The transmit path sizes headers using the wrapped `opt_flen`: - In `net/ipv6/ip6_output.c:1463-1465`: - `headersize = sizeof(struct ipv6hdr) + (opt ? opt->opt_flen + opt->opt_nflen : 0) + ...;` With wrapped `opt_flen`, `headersize`/headroom decisions underestimate what will be pushed later. 4. When building the final skb, the actual push length comes from `dst1opt` and is not limited by wrapped `opt_flen`: - In `net/ipv6/ip6_output.c:1930-1934`: - `if (opt->opt_flen) proto = ipv6_push_frag_opts(skb, opt, proto);` - In `net/ipv6/exthdrs.c:1206-1211`, `ipv6_push_frag_opts()` pushes `dst1opt` via `ipv6_push_exthdr()`. - In `net/ipv6/exthdrs.c:1179-1184`, `ipv6_push_exthdr()` does: - `skb_push(skb, ipv6_optlen(opt));` - `memcpy(h, opt, ipv6_optlen(opt));` With insufficient headroom, `skb_push()` underflows and triggers `skb_under_panic()` -> `BUG()`: - `net/core/skbuff.c:2669-2675` (`skb_push()` calls `skb_under_panic()`) - `net/core/skbuff.c:207-214` (`skb_panic()` ends in `BUG()`) - The `IPV6_DSTOPTS` cmsg path requires `CAP_NET_RAW` in the target netns user namespace (`ns_capable(net->user_ns, CAP_NET_RAW)`). - Root (or any task with `CAP_NET_RAW`) can trigger this without user namespaces. - An unprivileged `uid=1000` user can trigger this if unprivileged user namespaces are enabled and it can create a userns+netns to obtain namespaced `CAP_NET_RAW` (the attached PoC does this). - Local denial of service: kernel BUG/panic (system crash). - Reproducible with a small userspace PoC. This patch does not reject duplicated options, as this might break some user applications. Instead, it makes sure to adjust opt_flen and opt_nflen to correctly reflect the size of the current option headers, preventing the overflows and the potential for panics. This applies to IPV6_DSTOPTS, IPV6_HOPOPTS, and IPV6_RTHDR. Specifically: When a new IPV6_DSTOPTS is processed, the length of the old opt->dst1opt is subtracted from opt->opt_flen before adding the new length. When a new IPV6_HOPOPTS is processed, the length of the old opt->dst0opt is subtracted from opt->opt_nflen. When a new Routing Header (IPV6_RTHDR or IPV6_2292RTHDR) is processed, the length of the old opt->srcrt is subtracted from opt->opt_nflen. In the special case within IPV6_2292RTHDR handling where dst1opt is moved to dst0opt, the length of the old opt->dst0opt is subtracted from opt->opt_nflen before the new one is added. Fixes: 333fad5364d6 ("[IPV6]: Support several new sockopt / ancillary data in Advanced API (RFC3542).") Reported-by: Yiming Qian Closes: https://lore.kernel.org/netdev/CAL_bE8JNzawgr5OX5m+3jnQDHry2XxhQT5=jThW1zDPtUikRYA@mail.gmail.com/ Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260401154721.3740056-1-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv6/datagram.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c index e70ace403bbd0..4b8b9626428ca 100644 --- a/net/ipv6/datagram.c +++ b/net/ipv6/datagram.c @@ -761,6 +761,7 @@ int ip6_datagram_send_ctl(struct net *net, struct sock *sk, { struct in6_pktinfo *src_info; struct cmsghdr *cmsg; + struct ipv6_rt_hdr *orthdr; struct ipv6_rt_hdr *rthdr; struct ipv6_opt_hdr *hdr; struct ipv6_txoptions *opt = ipc6->opt; @@ -922,9 +923,13 @@ int ip6_datagram_send_ctl(struct net *net, struct sock *sk, goto exit_f; } if (cmsg->cmsg_type == IPV6_DSTOPTS) { + if (opt->dst1opt) + opt->opt_flen -= ipv6_optlen(opt->dst1opt); opt->opt_flen += len; opt->dst1opt = hdr; } else { + if (opt->dst0opt) + opt->opt_nflen -= ipv6_optlen(opt->dst0opt); opt->opt_nflen += len; opt->dst0opt = hdr; } @@ -967,12 +972,17 @@ int ip6_datagram_send_ctl(struct net *net, struct sock *sk, goto exit_f; } + orthdr = opt->srcrt; + if (orthdr) + opt->opt_nflen -= ((orthdr->hdrlen + 1) << 3); opt->opt_nflen += len; opt->srcrt = rthdr; if (cmsg->cmsg_type == IPV6_2292RTHDR && opt->dst1opt) { int dsthdrlen = ((opt->dst1opt->hdrlen+1)<<3); + if (opt->dst0opt) + opt->opt_nflen -= ipv6_optlen(opt->dst0opt); opt->opt_nflen += dsthdrlen; opt->dst0opt = opt->dst1opt; opt->dst1opt = NULL; -- 2.53.0