From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Ying Xue <ying.xue@windriver.com>
Cc: netfilter-devel@vger.kernel.org, davem@davemloft.net,
netdev@vger.kernel.org
Subject: Re: [net] netfilter: nat: sctp: fix ICMP packet to be dropped accidently
Date: Wed, 8 Mar 2017 18:29:43 +0100 [thread overview]
Message-ID: <20170308172943.GA8577@salvia> (raw)
In-Reply-To: <1488621602-4152-1-git-send-email-ying.xue@windriver.com>
On Sat, Mar 04, 2017 at 06:00:02PM +0800, Ying Xue wrote:
> Regarding RFC 792, the first 64 bits of the original SCTP datagram's
> data could be contained in ICMP packet, such as:
>
> 0 1 2 3
> 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Type | Code | Checksum |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | unused |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Internet Header + 64 bits of Original Data Datagram |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> However, according to RFC 4960, SCTP datagram header is as below:
>
> 0 1 2 3
> 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Source Port Number | Destination Port Number |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Verification Tag |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Checksum |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> It means only the first three fields of SCTP header can be carried in
> ICMP packet except for Checksum field.
>
> At present in sctp_manip_pkt(), no matter whether the packet is ICMP or
> not, it always calculates SCTP packet checksum. However, not only the
> calculation of checksum is unnecessary for ICMP, but also it causes
> another fatal issue that ICMP packet is dropped. The header size of
> SCTP is used to identify whether the writeable length of skb is bigger
> than skb->len through skb_make_writable() in sctp_manip_pkt(). But
> when it deals with ICMP packet, skb_make_writable() directly returns
> false as the writeable length of skb is bigger than skb->len.
> Subsequently ICMP is dropped.
>
> Now we correct this misbahavior. When sctp_manip_pkt() handles ICMP
> packet, 8 bytes rather than the whole SCTP header size is used to check
> if writeable length of skb is overflowed. Meanwhile, as it's meaningless
> to calculate checksum when packet is ICMP, the computation of checksum
> is ignored as well.
Applied, thanks.
prev parent reply other threads:[~2017-03-08 17:39 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-04 10:00 [net] netfilter: nat: sctp: fix ICMP packet to be dropped accidently Ying Xue
2017-03-08 17:29 ` Pablo Neira Ayuso [this message]
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