From: Eric Dumazet <eric.dumazet@gmail.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Eric Dumazet <edumazet@google.com>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
netdev <netdev@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: net: Fix skb csum races when peeking
Date: Tue, 14 Jul 2015 08:11:53 +0200 [thread overview]
Message-ID: <1436854313.1374.5.camel@edumazet-glaptop2.roam.corp.google.com> (raw)
In-Reply-To: <20150713120142.GA9787@gondor.apana.org.au>
On Mon, 2015-07-13 at 20:01 +0800, Herbert Xu wrote:
> ---8<---
> When we calculate the checksum on the recv path, we store the
> result in the skb as an optimisation in case we need the checksum
> again down the line.
>
> This is in fact bogus for the MSG_PEEK case as this is done without
> any locking. So multiple threads can peek and then store the result
> to the same skb, potentially resulting in bogus skb states.
>
> This patch fixes this by only storing the result if the skb is not
> shared. This preserves the optimisations for the few cases where
> it can be done safely due to locking or other reasons, e.g., SIOCINQ.
>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
>
> diff --git a/net/core/datagram.c b/net/core/datagram.c
> index b80fb91..4967262 100644
> --- a/net/core/datagram.c
> +++ b/net/core/datagram.c
> @@ -622,7 +657,8 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len)
> !skb->csum_complete_sw)
> netdev_rx_csum_fault(skb->dev);
> }
> - skb->csum_valid = !sum;
> + if (!skb_shared(skb))
> + skb->csum_valid = !sum;
> return sum;
> }
> EXPORT_SYMBOL(__skb_checksum_complete_head);
> @@ -642,11 +678,13 @@ __sum16 __skb_checksum_complete(struct sk_buff *skb)
> netdev_rx_csum_fault(skb->dev);
> }
>
> - /* Save full packet checksum */
> - skb->csum = csum;
> - skb->ip_summed = CHECKSUM_COMPLETE;
> - skb->csum_complete_sw = 1;
> - skb->csum_valid = !sum;
> + if (!skb_shared(skb)) {
> + /* Save full packet checksum */
> + skb->csum = csum;
> + skb->ip_summed = CHECKSUM_COMPLETE;
> + skb->csum_complete_sw = 1;
> + skb->csum_valid = !sum;
> + }
>
> return sum;
> }
Acked-by: Eric Dumazet <edumazet@google.com>
Thanks !
next prev parent reply other threads:[~2015-07-14 6:11 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-10 11:51 [PATCH] netlink: enable skb header refcounting before sending first broadcast Konstantin Khlebnikov
2015-07-10 13:49 ` Eric Dumazet
2015-07-10 14:08 ` Konstantin Khlebnikov
2015-07-13 7:23 ` Herbert Xu
2015-07-13 8:04 ` net: Clone skb before setting peeked flag Herbert Xu
2015-07-15 23:13 ` David Miller
2015-07-13 8:05 ` [PATCH] netlink: enable skb header refcounting before sending first broadcast Eric Dumazet
2015-07-13 8:10 ` Herbert Xu
2015-07-13 8:22 ` Eric Dumazet
2015-07-13 8:25 ` Herbert Xu
2015-07-13 8:28 ` Eric Dumazet
2015-07-13 8:31 ` Herbert Xu
2015-07-13 12:01 ` net: Fix skb csum races when peeking Herbert Xu
2015-07-13 14:25 ` Herbert Xu
2015-07-14 6:11 ` Eric Dumazet [this message]
2015-07-15 23:14 ` David Miller
2015-07-13 8:54 ` [PATCH] netlink: enable skb header refcounting before sending first broadcast Konstantin Khlebnikov
2015-07-13 9:04 ` Herbert Xu
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