kern/51555: Kernel panic in ifconfig when setting IP address in vx0

[Yeasah Pell]

The following reply was made to PR kern/51555; it has been noted by GNATS.

From: Yeasah Pell <yeasah at apocalypse.org>
To: freebsd-gnats-submit at FreeBSD.org, le at univie.ac.at,
	des at freebsd.org
Cc:  
Subject: Re: kern/51555: Kernel panic in ifconfig when setting IP address
 in vx0
Date: Sat, 07 Jun 2003 14:42:12 -0400

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 This bug was introduced in version 1.43 of /src/sys/dev/vx/if_vx.c. A 
 quick look at this change reveals an obvious error: 
 http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/dev/vx/if_vx.c.diff?r1=1.42&r2=1.43&f=h 
 
 
 The problem is that the ad-hoc mbuf packet header assert code was 
 replaced with the M_ASSERTPKTHDR macro, but this particular modification 
 goes too far in replacing a check for NULL mbuf by the macro 
 functionality. They aren't the same, since the function merely returns 
 if there is no mbuf, whereas the macro causes an assert.
 
 This certainly made the update from 5.0 to 5.1 more exciting... :-)
 
 Here is a patch to restore the NULL check:
 
 ---------------------------------
 
 --- if_vx.c     Tue Apr  8 10:25:44 2003
 +++ if_vx.c.fixed       Sat Jun  7 13:57:40 2003
 @@ -400,6 +400,9 @@
   startagain:
       /* Sneak a peek at the next packet */
       m = ifp->if_snd.ifq_head;
 +    if (m == NULL) {
 +        return;
 +    }
 
       /* We need to use m->m_pkthdr.len, so require the header */
       M_ASSERTPKTHDR(m);
 
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