netdev - Re: [PATCH net] net-timestamp: avoid use-after-free in ip_recv

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Date:   Mon, 17 Apr 2017 13:00:48 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, andreyknvl@...gle.com,
        eric.dumazet@...il.com, xiyou.wangcong@...il.com,
        willemb@...gle.com
Subject: Re: [PATCH net] net-timestamp: avoid use-after-free in
 ip_recv_error

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Wed, 12 Apr 2017 19:24:35 -0400

> From: Willem de Bruijn <willemb@...gle.com>
> 
> Syzkaller reported a use-after-free in ip_recv_error at line
> 
>     info->ipi_ifindex = skb->dev->ifindex;
> 
> This function is called on dequeue from the error queue, at which
> point the device pointer may no longer be valid.
> 
> Save ifindex on enqueue in __skb_complete_tx_timestamp, when the
> pointer is valid or NULL. Store it in temporary storage skb->cb.
> 
> It is safe to reference skb->dev here, as called from device drivers
> or dev_queue_xmit. The exception is when called from tcp_ack_tstamp;
> in that case it is NULL and ifindex is set to 0 (invalid).
> 
> Do not return a pktinfo cmsg if ifindex is 0. This maintains the
> current behavior of not returning a cmsg if skb->dev was NULL.
> 
> On dequeue, the ipv4 path will cast from sock_exterr_skb to
> in_pktinfo. Both have ifindex as their first element, so no explicit
> conversion is needed. This is by design, introduced in commit
> 0b922b7a829c ("net: original ingress device index in PKTINFO"). For
> ipv6 ip6_datagram_support_cmsg converts to in6_pktinfo.
> 
> Fixes: 829ae9d61165 ("net-timestamp: allow reading recv cmsg on errqueue with origin tstamp")
> 
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Applied and queued up for -stable, thanks.

In the future please don't insert empty lines between the Fixes: and
other tags.

Thanks.