netdev - Re: [PATCH] wireless: wext: allocate space for NULL-termination for 32byte SSIDs

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Date:	Wed, 16 Dec 2009 09:19:37 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Albert Cahalan <acahalan@...il.com>
Cc:	Holger Schurig <holgerschurig@...il.com>, m.hirsch@...mfeld.com,
	libertas-dev@...ts.infradead.org, dcbw@...hat.com,
	netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...nel.org, daniel@...aq.de,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] wireless: wext: allocate space for NULL-termination
 for 32byte SSIDs

On Wed, 2009-12-16 at 01:54 -0500, Albert Cahalan wrote:

> >> You therefore can't connect to the otherwise legitimate SSID of
> >> TEST\0\0\0.
> >
> > Ick! I guess your cfg80211 IBSS join handler needs to check for that
> > then and refuse such an SSID.
> 
> No, pad the SSID out to 32 bytes and let the firmware try.

No, if we _know_ the firmware will try to connect to "TEST" instead of
"TEST\0\0\0" then refusing it is the right thing to do.

> First of all, isn't TEST\0\0\0 simply the wrong length anyway?
> (that is, a length other than 32 is nonsense AFAIK)

No.

> Second of all, even if that is valid, the firmware probably handles
> at least one SSID that starts with TEST and has some number
> of NUL bytes on the end. Since you can't tell what that would be
> with a particular firmware version, you might as well just let the
> firmware try. The worst case failure here is that there is more than
> one SSID of this form and you connect to the wrong one. If you
> have a problem with this kind of trouble then you need ethernet.

No. An SSID is a uniquely defined, 1-32 byte long byte bit pattern. It
doesn't treat \0 special in any way as your comments suggest. If the
firmware stops matching at \0, the firmware is broken and shouldn't be
given a choice.

johannes

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