From: Sowmini Varadhan <sowmini.varadhan@oracle•com>
To: Eric Dumazet <eric.dumazet@gmail•com>
Cc: Alexander Duyck <aduyck@mirantis•com>,
netdev@vger•kernel.org, davem@davemloft•net,
alexander.duyck@gmail•com, tom@herbertland•com
Subject: Re: [net PATCH] flow_dissector: Fix unaligned access in __skb_flow_dissector when used by eth_get_headlen
Date: Sat, 30 Jan 2016 11:17:02 -0500 [thread overview]
Message-ID: <20160130161702.GA11601@oracle.com> (raw)
In-Reply-To: <1454124234.7627.119.camel@edumazet-glaptop2.roam.corp.google.com>
On (01/29/16 19:23), Eric Dumazet wrote:
> BTW, even a memcpy(&key_addrs->v4addrs, &iph->saddr, 8) could crash, as
> the compiler can certainly assume src and dst are 4 bytes aligned, and
> could use word accesses when inlining memcpy() even on Sparc.
>
> Apparently the compiler used by Sowmini is gentle.
One more subtlety that I missed until now..
eth_get_headlen passes in flow_keys_buf_dissector (NOT flow_keys_dissector!)
So FLOW_DISSECTOR_KEY_IPV4_ADDRS is not set, and this helps to dodge
the unaligned iph->saddr access.
But as others have pointed out, much of this code is brittle
because it's accessing the data before the driver has had a chance
to align things. The page_offset initialization of NET_IP_ALIGN,
with all its weaknesses, at least matches (in principle) the prescription
used for the xmit path.
--Sowmini
next prev parent reply other threads:[~2016-01-30 16:17 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-29 18:06 [RFC] Kernel unaligned access at __skb_flow_dissect Sowmini Varadhan
2016-01-29 18:33 ` Eric Dumazet
2016-01-29 18:40 ` Eric Dumazet
2016-01-29 19:08 ` David Miller
2016-01-29 19:39 ` Eric Dumazet
2016-01-29 18:54 ` Eric Dumazet
2016-01-29 19:22 ` Sowmini Varadhan
2016-01-29 21:00 ` Tom Herbert
2016-01-29 21:09 ` Sowmini Varadhan
2016-01-29 21:33 ` Tom Herbert
2016-01-29 23:00 ` Tom Herbert
2016-01-29 23:04 ` Sowmini Varadhan
2016-01-29 23:31 ` Tom Herbert
2016-01-29 23:58 ` Sowmini Varadhan
2016-01-30 0:47 ` Tom Herbert
2016-01-30 1:18 ` David Miller
2016-01-30 2:15 ` Eric Dumazet
2016-01-31 22:13 ` Tom Herbert
2016-02-01 0:04 ` Eric Dumazet
2016-01-29 19:06 ` David Miller
2016-01-29 19:37 ` Eric Dumazet
2016-01-29 19:41 ` David Miller
2016-01-29 19:44 ` Sowmini Varadhan
2016-01-29 20:01 ` Eric Dumazet
2016-01-29 20:06 ` Eric Dumazet
2016-01-29 21:16 ` Alexander Duyck
2016-01-29 21:33 ` Eric Dumazet
2016-01-29 22:08 ` Alexander Duyck
2016-01-29 22:28 ` Eric Dumazet
2016-01-29 23:00 ` Alexander Duyck
2016-02-01 16:55 ` David Laight
2016-02-01 17:25 ` Eric Dumazet
2016-01-29 19:04 ` David Miller
2016-01-30 2:49 ` [net PATCH] flow_dissector: Fix unaligned access in __skb_flow_dissector when used by eth_get_headlen Alexander Duyck
2016-01-30 3:23 ` Eric Dumazet
2016-01-30 3:35 ` David Miller
2016-01-30 4:46 ` Alexander Duyck
2016-01-30 16:17 ` Sowmini Varadhan [this message]
2016-01-30 17:43 ` Tom Herbert
2016-01-30 19:12 ` Sowmini Varadhan
2016-01-30 18:36 ` Alexander Duyck
2016-01-30 19:26 ` Eric Dumazet
2016-01-31 1:13 ` Alexander Duyck
2016-01-31 3:45 ` David Miller
2016-01-31 9:12 ` Alexander Duyck
2016-01-31 19:17 ` David Miller
2016-01-31 21:23 ` Sowmini Varadhan
2016-02-01 16:50 ` David Laight
2016-02-01 18:18 ` Alexander Duyck
2016-02-02 9:47 ` David Laight
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