From: Ido Schimmel <idosch@nvidia.com>
To: Eric Dumazet <edumazet@google.com>, zhilinz@nebusec.ai
Cc: Daehyeon Ko <4ncienth@gmail.com>,
netdev@vger.kernel.org, David Ahern <dsahern@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Simon Horman <horms@kernel.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net v3] ip: validate options before echoing them
Date: Wed, 2 Sep 2026 18:53:27 +0300 [thread overview]
Message-ID: <20260902155327.GA4024109@shredder> (raw)
In-Reply-To: <CANn89i+CSVHtjDk_NQT_Q6NpwJ76WQ=CExXp1xY15iPQuZSp+w@mail.gmail.com>
On Wed, Sep 02, 2026 at 10:44:45AM +0200, Eric Dumazet wrote:
> Oh well. Ai reviews will probably raise many bugs in this patch :/
>
> ipmr_cache_report() is a distinct bug and needs its own one liner fix.
>
> When ipmr_cache_report() builds an IGMPMSG_WHOLEPKT or IGMPMSG_WRVIFWHOLE
> report, it reallocates headroom and pushes a 20-byte iphdr with ihl = 5, but
> inherits pkt->cb with stale IPCB(skb)->opt offsets.
> Even if __ip_options_echo() rejects it, ip_cmsg_recv_opts() will still read
> stale IPCB(skb)->opt.optlen bytes from ip_hdr(skb) + 1 and leak packet data
> as IP_RECVOPTS.
> ipmr_cache_report() must clear IPCB(skb)->opt (or memset IPCB(skb)) when
> prepending the report header.
>
> Something like:
>
> diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> index e5f2b1c6150d2f6b2084c2ebaef6047db869cc87..72f1d620b8760722f805935d0299bac24a9f720c
> 100644
> --- a/net/ipv4/ipmr.c
> +++ b/net/ipv4/ipmr.c
> @@ -1102,6 +1102,7 @@ static int ipmr_cache_report(const struct mr_table *mrt,
> ip_hdr(skb)->ihl = sizeof(struct iphdr) >> 2;
> ip_hdr(skb)->tot_len = htons(ntohs(ip_hdr(pkt)->tot_len) +
> sizeof(struct iphdr));
> + memset(&IPCB(skb)->opt, 0, sizeof(IPCB(skb)->opt));
> } else {
> /* Copy the IP header */
> skb_set_network_header(skb, skb->len);
Yes, this was raised in the past [1].
Zhiling Zou, please send v4 of [2].
[1] https://lore.kernel.org/netdev/20260805081737.GA1284302@shredder/
[2] https://lore.kernel.org/netdev/e93d0d2fa5725ddd06b20e3e4223ab68b93b48d1.1785719031.git.zhilinz@nebusec.ai/
next prev parent reply other threads:[~2026-09-02 15:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-02 5:58 [PATCH net v3] ip: validate options before echoing them Daehyeon Ko
2026-09-02 8:44 ` Eric Dumazet
2026-09-02 15:53 ` Ido Schimmel [this message]
2026-09-02 9:29 ` Jiayuan Chen
2026-09-02 22:05 ` [syzbot ci] " syzbot ci
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