From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 4993B2D8378; Sun, 7 Jun 2026 10:45:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780829145; cv=none; b=mGNtAzjcVAfbpkUWaveEVmxPdLlF8XR4NE2lqlMeDZY1MphCUvjtvcBimzm5HiOXLfo2C7QkqiVo9uS+bqhHbCps8LJV+LHib/XBMLp93USpAUiShJ+OnwLBawD9wS/5DiYOlXzongMcfwBYQu69d+toTPeR1VwzJ2n6jkzjgxg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780829145; c=relaxed/simple; bh=KAucCjdqyNzAEMGn5Ai01fc0Gm9eWYQrBsxsT6o7lGI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=WuKR/3VDUUqwtTMAUzIGgK9Fl63hYP3pbb62U4N+vPFWl/lTG8hdjpdxk15cuewmPXtz+BnFYEq/fV3VW3SPBy0efzU9U3Ehvj0chD7q7vz4Of4jaiVDEi+HQ1xq9dGKmCHQvnsv4gs56Pkky4GstirBOGo4BuC9YIZQ4riqpNI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=TrzBhvRd; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="TrzBhvRd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 677621F00893; Sun, 7 Jun 2026 10:45:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780829144; bh=dco1Me2pkpA3XGv4lN3R+e4JR9E49p63U5HWKSnQMLA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=TrzBhvRdVNF2WzCKHGN8jV3WGYjmHu8z8R4Wehp+O64sZfSoQe6noMpF2zPWr0pBx +rWpDeMmHRyEvMv3h+q4RaFoxjpEiIURXQ8DXpuzBLyJJLMcPv+MSea2uWjb2q5D21 2g5u7ktPottsp/AiLN4jOMGEPCELyX6cBo81g7tU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Qi Tang , Willem de Bruijn , Jakub Kicinski Subject: [PATCH 6.12 190/307] ipv6: validate extension header length before copying to cmsg Date: Sun, 7 Jun 2026 11:59:47 +0200 Message-ID: <20260607095734.702386096@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260607095727.647295505@linuxfoundation.org> References: <20260607095727.647295505@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Qi Tang commit dd433671fef381fdaf7b530c631e6b782d66e224 upstream. 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 Link: https://patch.msgid.link/20260523143245.2281415-1-tpluszz77@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/ipv6/datagram.c | 54 ++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 46 insertions(+), 8 deletions(-) --- a/net/ipv6/datagram.c +++ b/net/ipv6/datagram.c @@ -617,6 +617,18 @@ void ip6_datagram_recv_common_ctl(struct } } +static u16 ipv6_get_exthdr_len(const struct sk_buff *skb, const u8 *ptr) +{ + u16 len; + + if (ptr + 2 > skb_tail_pointer(skb)) + return 0; + + len = (ptr[1] + 1) << 3; + + return (len <= skb_tail_pointer(skb) - ptr) ? len : 0; +} + void ip6_datagram_recv_specific_ctl(struct sock *sk, struct msghdr *msg, struct sk_buff *skb) { @@ -643,7 +655,10 @@ void ip6_datagram_recv_specific_ctl(stru /* HbH is allowed only once */ if (np->rxopt.bits.hopopts && (opt->flags & IP6SKB_HOPBYHOP)) { u8 *ptr = nh + sizeof(struct ipv6hdr); - put_cmsg(msg, SOL_IPV6, IPV6_HOPOPTS, (ptr[1]+1)<<3, ptr); + u16 len = ipv6_get_exthdr_len(skb, ptr); + + if (len) + put_cmsg(msg, SOL_IPV6, IPV6_HOPOPTS, len, ptr); } if (opt->lastopt && @@ -664,26 +679,37 @@ void ip6_datagram_recv_specific_ctl(stru 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; 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; } @@ -705,19 +731,31 @@ void ip6_datagram_recv_specific_ctl(stru } if (np->rxopt.bits.ohopopts && (opt->flags & IP6SKB_HOPBYHOP)) { u8 *ptr = nh + sizeof(struct ipv6hdr); - put_cmsg(msg, SOL_IPV6, IPV6_2292HOPOPTS, (ptr[1]+1)<<3, ptr); + u16 len = ipv6_get_exthdr_len(skb, ptr); + + if (len) + put_cmsg(msg, SOL_IPV6, IPV6_2292HOPOPTS, len, ptr); } if (np->rxopt.bits.odstopts && opt->dst0) { u8 *ptr = nh + opt->dst0; - put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, (ptr[1]+1)<<3, ptr); + u16 len = ipv6_get_exthdr_len(skb, ptr); + + if (len) + put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, len, ptr); } if (np->rxopt.bits.osrcrt && opt->srcrt) { struct ipv6_rt_hdr *rthdr = (struct ipv6_rt_hdr *)(nh + opt->srcrt); - put_cmsg(msg, SOL_IPV6, IPV6_2292RTHDR, (rthdr->hdrlen+1) << 3, rthdr); + u16 len = ipv6_get_exthdr_len(skb, (u8 *)rthdr); + + if (len) + put_cmsg(msg, SOL_IPV6, IPV6_2292RTHDR, len, rthdr); } if (np->rxopt.bits.odstopts && opt->dst1) { u8 *ptr = nh + opt->dst1; - put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, (ptr[1]+1)<<3, ptr); + u16 len = ipv6_get_exthdr_len(skb, ptr); + + if (len) + put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, len, ptr); } if (np->rxopt.bits.rxorigdstaddr) { struct sockaddr_in6 sin6;