netdev - Re: [PATCH V4 5/7] xen-netfront: reduce gso_max

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <51683F3902000078000CCD33@nat28.tlf.novell.com>
Date:	Fri, 12 Apr 2013 16:07:05 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Ian Campbell" <Ian.Campbell@...rix.com>,
	"Wei Liu" <wei.liu2@...rix.com>
Cc:	"David Vrabel" <david.vrabel@...rix.com>,
	"wdauchy@...il.com" <wdauchy@...il.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"annie.li@...cle.com" <annie.li@...cle.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH V4 5/7] xen-netfront: reduce gso_max_size to
 account for max TCP header

>>> On 12.04.13 at 16:44, Ian Campbell <Ian.Campbell@...rix.com> wrote:
> On Fri, 2013-04-12 at 15:24 +0100, Wei Liu wrote:
>> The maximum packet including header that can be handled by netfront / 
> netback
>> wire format is 65535. Reduce gso_max_size accordingly.
>> 
>> Drop skb and print warning when skb->len > 65535. This can 1) save the effort
>> to send malformed packet to netback, 2) help spotting misconfiguration of
>> netfront in the future.
>> 
>> Signed-off-by: Wei Liu <wei.liu2@...rix.com>
>> ---
>>  drivers/net/xen-netfront.c |   14 +++++++++++++-
>>  1 file changed, 13 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
>> index 1bb2e20..9c2eca1 100644
>> --- a/drivers/net/xen-netfront.c
>> +++ b/drivers/net/xen-netfront.c
>> @@ -547,6 +547,16 @@ static int xennet_start_xmit(struct sk_buff *skb, 
> struct net_device *dev)
>>  	unsigned int len = skb_headlen(skb);
>>  	unsigned long flags;
>>  
>> +	/* If skb->len is too big for wire format, drop skb and alert
>> +	 * user about misconfiguration.
>> +	 */
>> +	if (unlikely(skb->len > (typeof(tx->size))(~0))) {
> 
> This seems rather a complicated way of saying... er, something!
> 
> Perhaps we could have a #define in netif.h to compare against?
> 
> I'm not 100% convinced that the case and the ~ are in the right order to
> have the behaviour you want unless perhaps sizeof(tx->size) <
> sizeof(int). In any case it's too obfuscated for me ;-)

Previously this was (u16)~0, which I complained to have no
correlation to where the restriction actually comes from. Hence
the request to use typeof() on the very field that doesn't
permit a larger value.

Jan

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html