netdev - Re: [PATCH ipsec] esp6: fix check on ipv6_skip

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Message-ID: <20220315125843.GJ3581047@gauss3.secunet.de>
Date:   Tue, 15 Mar 2022 13:58:43 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Sabrina Dubroca <sd@...asysnail.net>
CC:     <netdev@...r.kernel.org>, Jordy Zomer <jordy@...ing.systems>,
        Xiumei Mu <xmu@...hat.com>
Subject: Re: [PATCH ipsec] esp6: fix check on ipv6_skip_exthdr's return value

On Thu, Mar 10, 2022 at 11:49:00AM +0100, Sabrina Dubroca wrote:
> Commit 5f9c55c8066b ("ipv6: check return value of ipv6_skip_exthdr")
> introduced an incorrect check, which leads to all ESP packets over
> either TCPv6 or UDPv6 encapsulation being dropped. In this particular
> case, offset is negative, since skb->data points to the ESP header in
> the following chain of headers, while skb->network_header points to
> the IPv6 header:
> 
>     IPv6 | ext | ... | ext | UDP | ESP | ...
> 
> That doesn't seem to be a problem, especially considering that if we
> reach esp6_input_done2, we're guaranteed to have a full set of headers
> available (otherwise the packet would have been dropped earlier in the
> stack). However, it means that the return value will (intentionally)
> be negative. We can make the test more specific, as the expected
> return value of ipv6_skip_exthdr will be the (negated) size of either
> a UDP header, or a TCP header with possible options.
> 
> In the future, we should probably either make ipv6_skip_exthdr
> explicitly accept negative offsets (and adjust its return value for
> error cases), or make ipv6_skip_exthdr only take non-negative
> offsets (and audit all callers).
> 
> Fixes: 5f9c55c8066b ("ipv6: check return value of ipv6_skip_exthdr")
> Reported-by: Xiumei Mu <xmu@...hat.com>
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>

Applied, thanks a lot Sabrina!