From: Ido Schimmel <idosch@nvidia.com>
To: Zihan Xi <zihanx@nebusec.ai>
Cc: netdev@vger.kernel.org, dsahern@kernel.org, davem@davemloft.net,
edumazet@google.com, pabeni@redhat.com, horms@kernel.org,
vega@nebusec.ai
Subject: Re: [PATCH net v2 1/1] ipv4: Fix fib_nlmsg_size() for RTA_VIA nexthops
Date: Thu, 30 Jul 2026 16:53:50 +0300 [thread overview]
Message-ID: <20260730135350.GA1789341@shredder> (raw)
In-Reply-To: <6f53fa797fcaeb26966432ed7ae9bb87c4961f37.1785411220.git.zihanx@nebusec.ai>
On Thu, Jul 30, 2026 at 12:59:26PM +0000, Zihan Xi wrote:
> fib_nlmsg_size() still estimates nexthop space as if every gateway is
> encoded as an IPv4 RTA_GATEWAY attribute. IPv4 routes can also carry an
> IPv6 gateway, which fib_nexthop_info() dumps as RTA_VIA.
>
> As a result, route notifications can allocate an skb that is too small.
> fib_dump_info() then fails with -EMSGSIZE and rtmsg_fib() hits the
> WARN_ON() that marks such failures as a fib_nlmsg_size() bug. With
> panic_on_warn set, this becomes a kernel panic.
>
> Mirror the actual nexthop dump layout in fib_nlmsg_size(): account for
> IPv6 nexthop gateways dumped as RTA_VIA, for the no-header rtnexthop
> layout used inside RTA_MULTIPATH, and for RTA_FLOW only when it is
> actually present.
>
> Fixes: d15662682db2 ("ipv4: Allow ipv6 gateway with ipv4 routes")
> Cc: stable@vger.kernel.org
> Reported-by: Vega <vega@nebusec.ai>
> Assisted-by: Codex:gpt-5.4
> Signed-off-by: Zihan Xi <zihanx@nebusec.ai>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
prev parent reply other threads:[~2026-07-30 13:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-30 12:59 [PATCH net v2 0/1] ipv4: Fix fib_nlmsg_size() for RTA_VIA nexthops Zihan Xi
2026-07-30 12:59 ` [PATCH net v2 1/1] " Zihan Xi
2026-07-30 13:53 ` Ido Schimmel [this message]
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