kern/132734: panic in net/if_mib.c

Robert Watson rwatson at
Thu Apr 23 19:40:05 UTC 2009

The following reply was made to PR kern/132734; it has been noted by GNATS.

From: Robert Watson <rwatson at>
To: Mikolaj Golub < at>
Cc: Alexey Illarionov <littlesavage at>, bug-followup at
Subject: Re: kern/132734: panic in net/if_mib.c
Date: Thu, 23 Apr 2009 20:33:43 +0100 (BST)

 On Thu, 23 Apr 2009, Mikolaj Golub wrote:
 > SVN rev 191435 on 2009-04-23 18:23:08Z by rwatson
 > Merge r191434 from stable/7 to releng/7.2:
 >  In sysctl_ifdata(), query the ifnet pointer using the index only
 >  once, rather than querying it, validating it, and then re-querying
 >  it without validating it.  This may avoid a NULL pointer
 >  dereference and resulting kernel page fault if an interface is
 >  being deleted while bsnmp or other tools are querying data on the
 >  interface.
 >  The full fix, to properly refcount the interface for the duration
 >  of the sysctl, is in 8.x, but is considered too high-risk for
 >  7.2, so instead will appear in 7.3 (if all goes well).
 > So, Alexey, can you try upgrading to the latest stable/7 or releng/7.2 or 
 > apply attached patch to see if this tweak at least eliminates the instant 
 > panic?
 I'll try to get the refcount fix into 7-STABLE in about two weeks, assuming no 
 hitches in the 8.x version.  This will close a number of related race 
 conditions, which we've had occasional reports of (and others that we 
 Robert N M Watson
 Computer Laboratory
 University of Cambridge

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