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[83.10.8.214]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c29de5e4ca9sm178474666b.42.2026.09.16.12.58.04 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 16 Sep 2026 12:58:05 -0700 (PDT) From: Norbert Szetei Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.700.51.1.1\)) Subject: [PATCH net v2] ipv6: do not let ipv6_find_hdr() return an offset past the packet end Message-Id: <8F80BA1A-DDFD-432D-9075-242A3435FEB5@doyensec.com> Date: Wed, 16 Sep 2026 21:57:53 +0200 Cc: David Ahern , Ido Schimmel , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Ilya Maximets , Aaron Conole , Eelco Chaudron , dev@openvswitch.org, linux-kernel@vger.kernel.org To: netdev@vger.kernel.org X-Mailer: Apple Mail (2.3864.700.51.1.1) ipv6_find_hdr() walks the extension header chain, skipping each header = by the length that header itself declares. ipv6_optlen() returns up to = 2048, and the skip is never checked against skb->len, so the offset stored in *offset can point past the end of the packet. openvswitch installs that offset as the transport header, and update_ipv6_checksum() then reads and writes the transport checksum = field out of bounds: BUG: KASAN: slab-use-after-free in = inet_proto_csum_replace16+0x445/0x470 Read of size 2 at addr ffff88810b754b06 by task ovs_ipv6_oob/629 CPU: 4 UID: 1000 PID: 629 Comm: ovs_ipv6_oob Tainted: G N 7.3.0-rc3+ = #348 Call Trace: inet_proto_csum_replace16+0x445/0x470 set_ipv6_addr+0x3dd/0x460 do_execute_actions+0x6a3d/0x7c40 ovs_execute_actions+0xfd/0x480 ovs_packet_cmd_execute+0xc38/0xf20 genl_rcv_msg+0x59e/0x870 netlink_rcv_skb+0x18b/0x450 genl_rcv+0x2d/0x40 netlink_unicast+0x6bc/0xa20 The buggy address belongs to the object at ffff88810b754980 which belongs to the cache skbuff_small_head of size 704 The buggy address is located 390 bytes inside of freed 704-byte region [ffff88810b754980, ffff88810b754c40) Other callers use that offset too, so bound it here rather than in one caller. Reject a header whose declared length does not fit in the packet. ipv6_find_hdr() already fails with -EBADMSG on a malformed chain, so = this adds no new failure mode. Fixes: f8f626754ebe ("ipv6: Move ipv6_find_hdr() out of Netfilter = code.") Suggested-by: Ilya Maximets Suggested-by: Eric Dumazet Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Norbert Szetei --- v2: - fix ipv6_find_hdr() instead of the openvswitch caller, per the = review of v1 - dropped the openvswitch change - retitled v1: = https://lore.kernel.org/netdev/114FAFBD-F7BC-46AE-AF9F-0D15124F130E@doyens= ec.com/ Reproducer available on request. net/ipv6/exthdrs_core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/ipv6/exthdrs_core.c b/net/ipv6/exthdrs_core.c index 9d06d487e8b1..4a9748338cf4 100644 --- a/net/ipv6/exthdrs_core.c +++ b/net/ipv6/exthdrs_core.c @@ -278,6 +278,9 @@ int ipv6_find_hdr(const struct sk_buff *skb, = unsigned int *offset, hdrlen =3D ipv6_optlen(hp); =20 if (!found) { + if (skb->len - start < hdrlen) + return -EBADMSG; + nexthdr =3D hp->nexthdr; start +=3D hdrlen; } --=20 2.55.0