netdev - Re: Fw: [Bug 13339] New: rtable leak in ipv4/route.c

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Message-ID: <20090519162330.GC28034@hmsreliant.think-freely.org>
Date:	Tue, 19 May 2009 12:23:30 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Jarek Poplawski <jarkao2@...il.com>, lav@....ru,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	netdev@...r.kernel.org
Subject: Re: Fw: [Bug 13339] New: rtable leak in ipv4/route.c

On Tue, May 19, 2009 at 05:32:29PM +0200, Eric Dumazet wrote:
> Jarek Poplawski a écrit :
> > On 19-05-2009 04:35, Stephen Hemminger wrote:
> >> Begin forwarded message:
> >>
> >> Date: Mon, 18 May 2009 14:10:20 GMT
> >> From: bugzilla-daemon@...zilla.kernel.org
> >> To: shemminger@...ux-foundation.org
> >> Subject: [Bug 13339] New: rtable leak in ipv4/route.c
> >>
> >>
> >> http://bugzilla.kernel.org/show_bug.cgi?id=13339
> > ...
> >> 2.6.29 patch has introduced flexible route cache rebuilding. Unfortunately the
> >> patch has at least one critical flaw, and another problem.
> >>
> >> rt_intern_hash calculates rthi pointer, which is later used for new entry
> >> insertion. The same loop calculates cand pointer which is used to clean the
> >> list. If the pointers are the same, rtable leak occurs, as first the cand is
> >> removed then the new entry is appended to it.
> >>
> >> This leak leads to unregister_netdevice problem (usage count > 0).
> >>
> >> Another problem of the patch is that it tries to insert the entries in certain
> >> order, to facilitate counting of entries distinct by all but QoS parameters.
> >> Unfortunately, referencing an existing rtable entry moves it to list beginning,
> >> to speed up further lookups, so the carefully built order is destroyed.
> 
> We could change rt_check_expire() to be smarter and handle any order in chains.
> 
> This would let rt_intern_hash() be simpler.
> 
> As its a more performance critical path, all would be good :)
> 
> >>
> >> For the first problem the simplest patch it to set rthi=0 when rthi==cand, but
> >> it will also destroy the ordering.
> > 
> > I think fixing this bug fast is more important than this
> > ordering or counting. Could you send your patch proposal?
> > 
> 

Of course, it helps if I attach the patch :)


diff --git a/include/net/dst.h b/include/net/dst.h
index 6be3b08..a39db6d 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -47,6 +47,7 @@ struct dst_entry
 #define DST_NOXFRM		2
 #define DST_NOPOLICY		4
 #define DST_NOHASH		8
+#define DST_GRPLDR		16
 	unsigned long		expires;
 
 	unsigned short		header_len;	/* more space at head required */
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index c4c60e9..0120f0e 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -610,6 +610,8 @@ static inline int ip_rt_proc_init(void)
 
 static inline void rt_free(struct rtable *rt)
 {
+	if (rt->u.dst.flags & DST_GRPLDR)
+		rt->u.dst.rt_next->u.dst.flag |= DST_GRPLDR;
 	call_rcu_bh(&rt->u.dst.rcu_head, dst_rcu_free);
 }
 
@@ -1143,8 +1145,11 @@ restart:
 		 * relvant to the hash function together, which we use to adjust
 		 * our chain length
 		 */
-		if (*rthp && compare_hash_inputs(&(*rthp)->fl, &rt->fl))
+		if (!*rthi && *rthp && 
+		    compare_hash_inputs(&(*rthp)->fl, &rt->fl) &&
+		    (cand != rth))
 			rthi = rth;
+		}
 	}
 
 	if (cand) {
@@ -1205,11 +1210,14 @@ restart:
 		}
 	}
 
-	if (rthi)
+	if (rthi) {
 		rt->u.dst.rt_next = rthi->u.dst.rt_next;
-	else
+		rthi->u.dst.flags &= ~(DST_GRPLDR);
+	} else
 		rt->u.dst.rt_next = rt_hash_table[hash].chain;
 
+	rt->u.dst.flags |= DST_GRPLDR;
+
 #if RT_CACHE_DEBUG >= 2
 	if (rt->u.dst.rt_next) {
 		struct rtable *trt;
--
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