netdev.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Christian Eggers <ceggers@arri.de>
To: Vladimir Oltean <olteanv@gmail.com>
Cc: Woojung Huh <woojung.huh@microchip.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	Kurt Kanzenbach <kurt@linutronix.de>
Subject: Re: [PATCH net] net: dsa: ksz: fix padding size of skb
Date: Wed, 14 Oct 2020 19:02:13 +0200	[thread overview]
Message-ID: <3253541.RgjG7ZtOS4@n95hx1g2> (raw)
In-Reply-To: <20201014165410.fzvzdk3odsdjljpq@skbuf>

Hi Vladimir,

On Wednesday, 14 October 2020, 18:54:10 CEST, Vladimir Oltean wrote:
> On Wed, Oct 14, 2020 at 07:47:50PM +0300, Vladimir Oltean wrote:
> > On Wed, Oct 14, 2020 at 06:17:19PM +0200, Christian Eggers wrote:
> > > __skb_put_padto() is called in order to ensure a minimal size of the
> > > sk_buff. The required minimal size is ETH_ZLEN + the size required for
> > > the tail tag.
> > > 
> > > The current argument misses the size for the tail tag. The expression
> > > "skb->len + padlen" can be simplified to ETH_ZLEN.
> > > 
> > > Too small sk_buffs typically result from cloning in
> > > dsa_skb_tx_timestamp(). The cloned sk_buff may not meet the minimum size
> > > requirements.
> > > 
> > > Fixes: e71cb9e00922 ("net: dsa: ksz: fix skb freeing")
> > > Signed-off-by: Christian Eggers <ceggers@arri.de>
> > > ---
> > 
> > Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
> 
> Actually no, I take that back.
> 
> This statement:
> > The expression "skb->len + padlen" can be simplified to ETH_ZLEN.
> 
> is false.
> skb->len + padlen == ETH_ZLEN only if skb->len is less than ETH_ZLEN.
ok, my comment is false.

> Otherwise, skb->len + padlen == skb->len.
> 
> Otherwise said, the frame must be padded to
> max(skb->len, ETH_ZLEN) + tail tag length.
At first I thought the same when working on this. But IMHO the padding must 
only ensure the minimum required size, there is no need to pad to the "real" 
size of the skb. The check for the tailroom above ensures that enough memory 
for the "real" size is available.

> So please keep the "skb->len + padlen + len".
> 
> Thanks,
> -Vladimir
Best regards
Christian




  reply	other threads:[~2020-10-14 17:03 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-14 16:17 Christian Eggers
2020-10-14 16:47 ` Vladimir Oltean
2020-10-14 16:54   ` Vladimir Oltean
2020-10-14 17:02     ` Christian Eggers [this message]
2020-10-14 17:31       ` Vladimir Oltean
2020-10-15 17:58         ` Christian Eggers
2020-10-16  7:45           ` Kurt Kanzenbach
2020-10-16  9:00             ` Christian Eggers
2020-10-16  9:05               ` Vladimir Oltean
2020-10-16 12:44                 ` Christian Eggers
2020-10-16 15:56                   ` Vladimir Oltean
2020-10-16 18:03                     ` Jakub Kicinski
2020-10-16 18:13                       ` Vladimir Oltean
2020-10-16 18:52                         ` Jakub Kicinski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=3253541.RgjG7ZtOS4@n95hx1g2 \
    --to=ceggers@arri.de \
    --cc=UNGLinuxDriver@microchip.com \
    --cc=andrew@lunn.ch \
    --cc=davem@davemloft.net \
    --cc=f.fainelli@gmail.com \
    --cc=kuba@kernel.org \
    --cc=kurt@linutronix.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=olteanv@gmail.com \
    --cc=vivien.didelot@gmail.com \
    --cc=woojung.huh@microchip.com \
    --subject='Re: [PATCH net] net: dsa: ksz: fix padding size of skb' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).