Subject: Re: [PATCH] iptables: xt_hashlimit fix

From: Eric Dumazet <[email-masked]>
Date: Sat, 28 Feb 2009 07:56:54 +0100

Jan Engelhardt a écrit :
> On Friday 2009-02-20 19:33, Jan Engelhardt wrote:
>> On Friday 2009-02-20 19:10, Eric Dumazet wrote:
>>> Damned this broke xt_hashlimit, version=0
>>> Look file "net/netfilter/xt_hashlimit.c" line 706
>>>
>>>    /* Ugly hack: For SMP, we only want to use one set */
>>>    r->u.master = r;
>>>
>>> So, it appears some modules are using pointers to themselves, what a hack :(
>>> We probably need an audit of other modules.
>> xt_limit and xt_statistic are affected; I'll happily fix that up.
> 
> Please have a look!
> 
> ---8<---
> parent b2bd9ab764d65237232c4aad5ab8d5d8b5714f72 (v2.6.29-rc6-31-gb2bd9ab)
> commit 3e7ee1dcc808b8eec82eddfa0436f78e31d2004a
> Author: Jan Engelhardt <[email-masked]>
> Date:   Sat Feb 28 02:49:28 2009 +0100
> 
> netfilter: xtables: avoid pointer to self
> 
> Signed-off-by: Jan Engelhardt <[email-masked]>

Seems good to me ! Thanks Jan !

Reviewed-by: Eric Dumazet <[email-masked]>

Are you sure xt_quota doesnt need some tweak, or should we not care of changes
done in quota while temporary tables are installed (iptables -L) ?

> ---
>  include/linux/netfilter/xt_limit.h     |    9 +++--
>  include/linux/netfilter/xt_statistic.h |    7 ++--
>  net/netfilter/xt_limit.c               |   40 +++++++++++++++++------
>  net/netfilter/xt_statistic.c           |   28 +++++++++++++---
>  4 files changed, 61 insertions(+), 23 deletions(-)
> 
> diff --git a/include/linux/netfilter/xt_limit.h b/include/linux/netfilter/xt_limit.h
> index b3ce653..fda222c 100644
> --- a/include/linux/netfilter/xt_limit.h
> +++ b/include/linux/netfilter/xt_limit.h
> @@ -4,6 +4,8 @@
>  /* timings are in milliseconds. */
>  #define XT_LIMIT_SCALE 10000
>  
> +struct xt_limit_priv;
> +
>  /* 1/10,000 sec period => max of 10,000/sec.  Min rate is then 429490
>     seconds, or one every 59 hours. */
>  struct xt_rateinfo {
> @@ -11,11 +13,10 @@ struct xt_rateinfo {
>  	u_int32_t burst;  /* Period multiplier for upper limit. */
>  
>  	/* Used internally by the kernel */
> -	unsigned long prev;
> -	u_int32_t credit;
> +	unsigned long prev; /* moved to xt_limit_priv */
> +	u_int32_t credit; /* moved to xt_limit_priv */
>  	u_int32_t credit_cap, cost;
>  
> -	/* Ugly, ugly fucker. */
> -	struct xt_rateinfo *master;
> +	struct xt_limit_priv *master;
>  };
>  #endif /*_XT_RATE_H*/
> diff --git a/include/linux/netfilter/xt_statistic.h b/include/linux/netfilter/xt_statistic.h
> index 3d38bc9..8f521ab 100644
> --- a/include/linux/netfilter/xt_statistic.h
> +++ b/include/linux/netfilter/xt_statistic.h
> @@ -13,6 +13,8 @@ enum xt_statistic_flags {
>  };
>  #define XT_STATISTIC_MASK		0x1
>  
> +struct xt_statistic_priv;
> +
>  struct xt_statistic_info {
>  	u_int16_t			mode;
>  	u_int16_t			flags;
> @@ -23,11 +25,10 @@ struct xt_statistic_info {
>  		struct {
>  			u_int32_t	every;
>  			u_int32_t	packet;
> -			/* Used internally by the kernel */
> -			u_int32_t	count;
> +			u_int32_t	count; /* unused */
>  		} nth;
>  	} u;
> -	struct xt_statistic_info	*master __attribute__((aligned(8)));
> +	struct xt_statistic_priv *master __attribute__((aligned(8)));
>  };
>  
>  #endif /* _XT_STATISTIC_H */
> diff --git a/net/netfilter/xt_limit.c b/net/netfilter/xt_limit.c
> index c908d69..2e8089e 100644
> --- a/net/netfilter/xt_limit.c
> +++ b/net/netfilter/xt_limit.c
> @@ -14,6 +14,11 @@
>  #include <linux/netfilter/x_tables.h>
>  #include <linux/netfilter/xt_limit.h>
>  
> +struct xt_limit_priv {
> +	unsigned long prev;
> +	uint32_t credit;
> +};
> +
>  MODULE_LICENSE("GPL");
>  MODULE_AUTHOR("Herve Eychenne <[email-masked]>");
>  MODULE_DESCRIPTION("Xtables: rate-limit match");
> @@ -60,18 +65,18 @@ static DEFINE_SPINLOCK(limit_lock);
>  static bool
>  limit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
>  {
> -	struct xt_rateinfo *r =
> -		((const struct xt_rateinfo *)par->matchinfo)->master;
> +	const struct xt_rateinfo *r = par->matchinfo;
> +	struct xt_limit_priv *priv = r->master;
>  	unsigned long now = jiffies;
>  
>  	spin_lock_bh(&limit_lock);
> -	r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
> -	if (r->credit > r->credit_cap)
> -		r->credit = r->credit_cap;
> +	priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
> +	if (priv->credit > r->credit_cap)
> +		priv->credit = r->credit_cap;
>  
> -	if (r->credit >= r->cost) {
> +	if (priv->credit >= r->cost) {
>  		/* We're not limited. */
> -		r->credit -= r->cost;
> +		priv->credit -= r->cost;
>  		spin_unlock_bh(&limit_lock);
>  		return true;
>  	}
> @@ -95,6 +100,7 @@ user2credits(u_int32_t user)
>  static bool limit_mt_check(const struct xt_mtchk_param *par)
>  {
>  	struct xt_rateinfo *r = par->matchinfo;
> +	struct xt_limit_priv *priv;
>  
>  	/* Check for overflow. */
>  	if (r->burst == 0
> @@ -104,19 +110,30 @@ static bool limit_mt_check(const struct xt_mtchk_param *par)
>  		return false;
>  	}
>  
> -	/* For SMP, we only want to use one set of counters. */
> -	r->master = r;
> +	priv = kmalloc(sizeof(*priv), GFP_KERNEL);
> +	if (priv == NULL)
> +		return -ENOMEM;
> +
> +	/* For SMP, we only want to use one set of state. */
> +	r->master = priv;
>  	if (r->cost == 0) {
>  		/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
>  		   128. */
> -		r->prev = jiffies;
> -		r->credit = user2credits(r->avg * r->burst);	 /* Credits full. */
> +		priv->prev = jiffies;
> +		priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
>  		r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
>  		r->cost = user2credits(r->avg);
>  	}
>  	return true;
>  }
>  
> +static void limit_mt_destroy(const struct xt_mtdtor_param *par)
> +{
> +	const struct xt_rateinfo *info = par->matchinfo;
> +
> +	kfree(info->master);
> +}
> +
>  #ifdef CONFIG_COMPAT
>  struct compat_xt_rateinfo {
>  	u_int32_t avg;
> @@ -167,6 +184,7 @@ static struct xt_match limit_mt_reg __read_mostly = {
>  	.family           = NFPROTO_UNSPEC,
>  	.match            = limit_mt,
>  	.checkentry       = limit_mt_check,
> +	.destroy          = limit_mt_destroy,
>  	.matchsize        = sizeof(struct xt_rateinfo),
>  #ifdef CONFIG_COMPAT
>  	.compatsize       = sizeof(struct compat_xt_rateinfo),
> diff --git a/net/netfilter/xt_statistic.c b/net/netfilter/xt_statistic.c
> index 0d75141..d8c0f8f 100644
> --- a/net/netfilter/xt_statistic.c
> +++ b/net/netfilter/xt_statistic.c
> @@ -16,6 +16,10 @@
>  #include <linux/netfilter/xt_statistic.h>
>  #include <linux/netfilter/x_tables.h>
>  
> +struct xt_statistic_priv {
> +	uint32_t count;
> +};
> +
>  MODULE_LICENSE("GPL");
>  MODULE_AUTHOR("Patrick McHardy <[email-masked]>");
>  MODULE_DESCRIPTION("Xtables: statistics-based matching (\"Nth\", random)");
> @@ -27,7 +31,7 @@ static DEFINE_SPINLOCK(nth_lock);
>  static bool
>  statistic_mt(const struct sk_buff *skb, const struct xt_match_param *par)
>  {
> -	struct xt_statistic_info *info = (void *)par->matchinfo;
> +	const struct xt_statistic_info *info = par->matchinfo;
>  	bool ret = info->flags & XT_STATISTIC_INVERT;
>  
>  	switch (info->mode) {
> @@ -36,10 +40,9 @@ statistic_mt(const struct sk_buff *skb, const struct xt_match_param *par)
>  			ret = !ret;
>  		break;
>  	case XT_STATISTIC_MODE_NTH:
> -		info = info->master;
>  		spin_lock_bh(&nth_lock);
> -		if (info->u.nth.count++ == info->u.nth.every) {
> -			info->u.nth.count = 0;
> +		if (info->master->count++ == info->u.nth.every) {
> +			info->master->count = 0;
>  			ret = !ret;
>  		}
>  		spin_unlock_bh(&nth_lock);
> @@ -56,16 +59,31 @@ static bool statistic_mt_check(const struct xt_mtchk_param *par)
>  	if (info->mode > XT_STATISTIC_MODE_MAX ||
>  	    info->flags & ~XT_STATISTIC_MASK)
>  		return false;
> -	info->master = info;
> +
> +	info->master = kzalloc(sizeof(*info->master), GFP_KERNEL);
> +	if (info->master == NULL) {
> +		printk(KERN_ERR KBUILD_MODNAME ": Out of memory\n");
> +		return false;
> +	}
> +	info->master->count = info->u.nth.count;
> +
>  	return true;
>  }
>  
> +static void statistic_mt_destroy(const struct xt_mtdtor_param *par)
> +{
> +	const struct xt_statistic_info *info = par->matchinfo;
> +
> +	kfree(info->master);
> +}
> +
>  static struct xt_match xt_statistic_mt_reg __read_mostly = {
>  	.name       = "statistic",
>  	.revision   = 0,
>  	.family     = NFPROTO_UNSPEC,
>  	.match      = statistic_mt,
>  	.checkentry = statistic_mt_check,
> +	.destroy    = statistic_mt_destroy,
>  	.matchsize  = sizeof(struct xt_statistic_info),
>  	.me         = THIS_MODULE,
>  };

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