From ee319bd3a0e976af5087cbe59ebc50a66f31d202 Mon Sep 17 00:00:00 2001 From: Norbert Szetei Date: Wed, 16 Sep 2026 21:57:53 +0200 Subject: [PATCH] ipv6: do not let ipv6_find_hdr() return an offset past the packet end 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 Signed-off-by: Norbert Szetei Reviewed-by: Ido Schimmel Reviewed-by: Ilya Maximets Link: https://patch.msgid.link/8F80BA1A-DDFD-432D-9075-242A3435FEB5@doyensec.com Signed-off-by: Jakub Kicinski --- 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 = ipv6_optlen(hp); if (!found) { + if (skb->len - start < hdrlen) + return -EBADMSG; + nexthdr = hp->nexthdr; start += hdrlen; }