netdev - Re: [BUG] 2.6.37-rc5 Memory leak in net/ipv4/udp.c

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Date:	Fri, 17 Dec 2010 12:11:43 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [BUG] 2.6.37-rc5 Memory leak in net/ipv4/udp.c

Hi,

Eric Dumazet writes:
> Le vendredi 17 décembre 2010 à 11:18 +0100, Lothar Waßmann a écrit :
> > The offending code in net/ipv4/udp.c is:
> > |void __init udp_table_init(struct udp_table *table, const char *name)
> > |{
> > |	unsigned int i;
> > |
> > |	if (!CONFIG_BASE_SMALL)
> > |		table->hash = alloc_large_system_hash(name,
> > |			2 * sizeof(struct udp_hslot),
> > |			uhash_entries,
> > |			21, /* one slot per 2 MB */
> > |			0,
> > |			&table->log,
> > |			&table->mask,
> > |			64 * 1024);
> > |	/*
> > |	 * Make sure hash table has the minimum size
> > |	 */
> > |	if (CONFIG_BASE_SMALL || table->mask < UDP_HTABLE_SIZE_MIN - 1) {
> > |		table->hash = kmalloc(UDP_HTABLE_SIZE_MIN *
> > |				      2 * sizeof(struct udp_hslot), GFP_KERNEL);
> > In case of !CONFIG_BASE_SMALL and 'table->mask < UDP_HTABLE_SIZE_MIN - 1)'
> > the memory allocated in the previous if clause becomes inacessible!
> > 
> > Shouldn't this be:
> > |	if (!CONFIG_BASE_SMALL && table->mask >= UDP_HTABLE_SIZE_MIN - 1) {
> > |		table->hash = alloc_large_system_hash(name,
> > |			2 * sizeof(struct udp_hslot),
> > |			uhash_entries,
> > |			21, /* one slot per 2 MB */
> > |			0,
> > |			&table->log,
> > |			&table->mask,
> > |			64 * 1024);
> > |	} else {
> > |		table->hash = kmalloc(UDP_HTABLE_SIZE_MIN *
> > |				      2 * sizeof(struct udp_hslot), GFP_KERNEL);
> > [...]
> > 
> 
> Nothing we can do about it, there is no API to reverse the
> alloc_large_system_hash() effect. We could call kmemleak api to at least
> avoid this false alarm.
> 
Do you have to call it at all in case of table->mask < UDP_HTABLE_SIZE_MIN - 1?

> We really want a minimum size for the UDP hash table, because our algos
> depend on this.
> 
I can't see why this could not be achieved by doing _either_
alloc_large_system_hash() _OR_ kmalloc() as stated above, but not
both.


Lothar Waßmann
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