linux-kernel - Re: softmac possible null deref [was: Complete report of Null dereference errors in kernel 2.6.17.1]

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Date:	Mon, 24 Jul 2006 17:00:08 -0700
From:	Thomas Dillig <tdillig@...nford.edu>
To:	Daniel Drake <dsd@...too.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: softmac possible null deref [was: Complete report of Null dereference
 errors in kernel 2.6.17.1]



>
> Either I'm misunderstanding, or this is bogus.
>
> when *pkt is allocated by the various child functions (e.g. 
> ieee80211softmac_disassoc_deauth), it is always checked for NULL 
> before being used.
>
> Finally, line 453 does another NULL check, so that any failures 
> generated above are handled appropriately.
>
> What is the report trying to say?
>
> Daniel
>
> -
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>
Hi,

At least in 2.6.17.1, the function looks as follows:

 /* Create an rts/cts frame */
445 static u32
446 ieee80211softmac_rts_cts(struct ieee80211_hdr_2addr **pkt,
447         struct ieee80211softmac_device *mac, struct 
ieee80211softmac_network *net,
448         u32 type)
449 {
450         /* Allocate Packet */
451         (*pkt) = kmalloc(IEEE80211_2ADDR_LEN, GFP_ATOMIC);     
452         memset(*pkt, 0, IEEE80211_2ADDR_LEN); //*pkt is not checked 
for NULL
453         if((*pkt) == NULL) //*pkt is checked for NULL
454                 return 0;
455         ieee80211softmac_hdr_2addr(mac, (*pkt), type, net->bssid);
456         return IEEE80211_2ADDR_LEN;
457 }

The report is just trying to say that "*pkt" is dereferenced inside the 
call to "memset" and checked for being null one line later.

I hope this clarifies the message,
-Tom
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