netdev - Re: [PATCH] tcp: Don't access TCP_SKB

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Message-Id: <20190311.153732.195292246386219923.davem@davemloft.net>
Date:   Mon, 11 Mar 2019 15:37:32 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     cpaasch@...le.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com
Subject: Re: [PATCH] tcp: Don't access TCP_SKB_CB before initializing it

From: Christoph Paasch <cpaasch@...le.com>
Date: Mon, 11 Mar 2019 11:41:05 -0700

> Since commit eeea10b83a13 ("tcp: add
> tcp_v4_fill_cb()/tcp_v4_restore_cb()"), tcp_vX_fill_cb is only called
> after tcp_filter(). That means, TCP_SKB_CB(skb)->end_seq still points to
> the IP-part of the cb.
> 
> We thus should not mock with it, as this can trigger bugs (thanks
> syzkaller):
> [   12.349396] ==================================================================
> [   12.350188] BUG: KASAN: slab-out-of-bounds in ip6_datagram_recv_specific_ctl+0x19b3/0x1a20
> [   12.351035] Read of size 1 at addr ffff88006adbc208 by task test_ip6_datagr/1799
> 
> Setting end_seq is actually no more necessary in tcp_filter as it gets
> initialized later on in tcp_vX_fill_cb.
> 
> Cc: Eric Dumazet <edumazet@...gle.com>
> Fixes: eeea10b83a13 ("tcp: add tcp_v4_fill_cb()/tcp_v4_restore_cb()")
> Signed-off-by: Christoph Paasch <cpaasch@...le.com>

Applied.