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| author | Eric Dumazet <edumazet@google.com> | 2026-03-26 20:26:08 +0000 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-03-27 20:22:46 -0700 |
| commit | 86ab3e55673a7a49a841838776f1ab18d23a67b5 (patch) | |
| tree | adcbb35f9aadcefc6ff5a15a4fab7e14a9a0653f /net/ipv6 | |
| parent | 5597dd284ff8c556c0b00f6a34473677426e3f81 (diff) | |
| download | lwn-86ab3e55673a7a49a841838776f1ab18d23a67b5.tar.gz lwn-86ab3e55673a7a49a841838776f1ab18d23a67b5.zip | |
ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()
Sashiko AI-review observed:
In ip6_err_gen_icmpv6_unreach(), the skb is an outer IPv4 ICMP error packet
where its cb contains an IPv4 inet_skb_parm. When skb is cloned into skb2
and passed to icmp6_send(), it uses IP6CB(skb2).
IP6CB interprets the IPv4 inet_skb_parm as an inet6_skb_parm. The cipso
offset in inet_skb_parm.opt directly overlaps with dsthao in inet6_skb_parm
at offset 18.
If an attacker sends a forged ICMPv4 error with a CIPSO IP option, dsthao
would be a non-zero offset. Inside icmp6_send(), mip6_addr_swap() is called
and uses ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO).
This would scan the inner, attacker-controlled IPv6 packet starting at that
offset, potentially returning a fake TLV without checking if the remaining
packet length can hold the full 18-byte struct ipv6_destopt_hao.
Could mip6_addr_swap() then perform a 16-byte swap that extends past the end
of the packet data into skb_shared_info?
Should the cb array also be cleared in ip6_err_gen_icmpv6_unreach() and
ip6ip6_err() to prevent this?
This patch implements the first suggestion.
I am not sure if ip6ip6_err() needs to be changed.
A separate patch would be better anyway.
Fixes: ca15a078bd90 ("sit: generate icmpv6 error when receiving icmpv4 error")
Reported-by: Ido Schimmel <idosch@nvidia.com>
Closes: https://sashiko.dev/#/patchset/20260326155138.2429480-1-edumazet%40google.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Oskar Kjos <oskar.kjos@hotmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260326202608.2976021-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv6')
| -rw-r--r-- | net/ipv6/icmp.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c index 813d2e9edb8b..d5d23a9296ea 100644 --- a/net/ipv6/icmp.c +++ b/net/ipv6/icmp.c @@ -875,6 +875,9 @@ int ip6_err_gen_icmpv6_unreach(struct sk_buff *skb, int nhs, int type, if (!skb2) return 1; + /* Remove debris left by IPv4 stack. */ + memset(IP6CB(skb2), 0, sizeof(*IP6CB(skb2))); + skb_dst_drop(skb2); skb_pull(skb2, nhs); skb_reset_network_header(skb2); |