linux/net/ipv6
Daniel Borkmann 076b8cad77 ipv6: Cap TLV scan in ip6_tnl_parse_tlv_enc_lim
Commit 47d3d7ac65 ("ipv6: Implement limits on Hop-by-Hop and
Destination options") added net.ipv6.max_{hbh,dst}_opts_{cnt,len}
and applied them in ip6_parse_tlv(), the generic TLV walker
invoked from ipv6_destopt_rcv() and ipv6_parse_hopopts().

ip6_tnl_parse_tlv_enc_lim() does not go through ip6_parse_tlv();
it has its own hand-rolled TLV scanner inside its NEXTHDR_DEST
branch which looks for IPV6_TLV_TNL_ENCAP_LIMIT. That inner
loop is bounded only by optlen, which can be up to 2048 bytes.
Stuffing the Destination Options header with 2046 Pad1 (type=0)
entries advances the scanner a single byte at a time, yielding
~2000 TLV iterations per extension header.

Reusing max_dst_opts_cnt to bound the TLV iterations, matching
the semantics from 47d3d7ac65, would require duplicating
ip6_parse_tlv() to also validate Pad1/PadN payload. It would
also mandate enforcing max_dst_opts_len, since otherwise an
attacker shifts the axis to few options with a giant PadN and
recovers the original DoS. Allowing up to 8 options before the
tunnel encapsulation limit TLV is liberal enough; in practice
encap limit is the first TLV. Thus, go with a hard-coded limit
IP6_TUNNEL_MAX_DEST_TLVS (8).

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Justin Iurman <justin.iurman@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-04-23 11:52:07 -07:00
..
ila
netfilter
Kconfig
Makefile
addrconf.c
addrconf_core.c
addrlabel.c
af_inet6.c
ah6.c
anycast.c
calipso.c
datagram.c
esp6.c
esp6_offload.c
exthdrs.c
exthdrs_core.c
exthdrs_offload.c
fib6_notifier.c
fib6_rules.c
fou6.c
icmp.c
inet6_connection_sock.c
inet6_hashtables.c
ioam6.c
ioam6_iptunnel.c
ip6_checksum.c
ip6_fib.c
ip6_flowlabel.c
ip6_gre.c
ip6_icmp.c
ip6_input.c
ip6_offload.c
ip6_offload.h
ip6_output.c
ip6_tunnel.c ipv6: Cap TLV scan in ip6_tnl_parse_tlv_enc_lim 2026-04-23 11:52:07 -07:00
ip6_udp_tunnel.c
ip6_vti.c
ip6mr.c
ipcomp6.c
ipv6_sockglue.c
mcast.c
mcast_snoop.c
mip6.c
ndisc.c
netfilter.c
output_core.c
ping.c
proc.c
protocol.c
raw.c
reassembly.c
route.c
rpl.c
rpl_iptunnel.c
seg6.c
seg6_hmac.c
seg6_iptunnel.c
seg6_local.c
sit.c
syncookies.c
sysctl_net_ipv6.c
tcp_ao.c
tcp_ipv6.c
tcpv6_offload.c
tunnel6.c
udp.c
udp_offload.c
xfrm6_input.c
xfrm6_output.c
xfrm6_policy.c
xfrm6_protocol.c
xfrm6_state.c
xfrm6_tunnel.c