[PATCH 1/2] netfilter: fix the hash random initializing race

[PATCH 1/2] netfilter: fix the hash random initializing race

[Changli Gao]

nf_conntrack_alloc() isn't called with nf_conntrack_lock locked, so hash
random initializing code maybe executed more than once on different CPUs.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
---
 net/netfilter/nf_conntrack_core.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index df3eedb..7ae7f71 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -65,8 +65,7 @@ EXPORT_SYMBOL_GPL(nf_conntrack_max);
 DEFINE_PER_CPU(struct nf_conn, nf_conntrack_untracked);
 EXPORT_PER_CPU_SYMBOL(nf_conntrack_untracked);
 
-static int nf_conntrack_hash_rnd_initted;
-static unsigned int nf_conntrack_hash_rnd;
+static unsigned int nf_conntrack_hash_rnd __read_mostly;
 
 static u_int32_t __hash_conntrack(const struct nf_conntrack_tuple *tuple,
 				  u16 zone, unsigned int size, unsigned int rnd)
@@ -574,10 +573,16 @@ struct nf_conn *nf_conntrack_alloc(struct net *net, u16 zone,
 {
 	struct nf_conn *ct;
 
-	if (unlikely(!nf_conntrack_hash_rnd_initted)) {
-		get_random_bytes(&nf_conntrack_hash_rnd,
-				sizeof(nf_conntrack_hash_rnd));
-		nf_conntrack_hash_rnd_initted = 1;
+	if (unlikely(!nf_conntrack_hash_rnd)) {
+		unsigned int rand;
+
+		/* Why not initialize nf_conntrack_rnd in a "init()" function ?
+		 * Because there isn't enough entropy when system initializing,
+		 * and we initialize it as late as possible. */
+		do {
+			get_random_bytes(&rand, sizeof(rand));
+		} while (!rand);
+		cmpxchg(&nf_conntrack_hash_rnd, 0, rand);
 	}
 
 	/* We don't want any race condition at early drop stage */

Re: [PATCH 1/2] netfilter: fix the hash random initializing race

[Eric Dumazet]

Le samedi 21 août 2010 à 00:06 +0800, Changli Gao a écrit :
> nf_conntrack_alloc() isn't called with nf_conntrack_lock locked, so hash
> random initializing code maybe executed more than once on different CPUs.
> 
> Signed-off-by: Changli Gao <xiaosuo@gmail.com>
> ---
>  net/netfilter/nf_conntrack_core.c |   17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
> index df3eedb..7ae7f71 100644
> --- a/net/netfilter/nf_conntrack_core.c
> +++ b/net/netfilter/nf_conntrack_core.c
> @@ -65,8 +65,7 @@ EXPORT_SYMBOL_GPL(nf_conntrack_max);
>  DEFINE_PER_CPU(struct nf_conn, nf_conntrack_untracked);
>  EXPORT_PER_CPU_SYMBOL(nf_conntrack_untracked);
>  
> -static int nf_conntrack_hash_rnd_initted;
> -static unsigned int nf_conntrack_hash_rnd;
> +static unsigned int nf_conntrack_hash_rnd __read_mostly;
>  
>  static u_int32_t __hash_conntrack(const struct nf_conntrack_tuple *tuple,
>  				  u16 zone, unsigned int size, unsigned int rnd)
> @@ -574,10 +573,16 @@ struct nf_conn *nf_conntrack_alloc(struct net *net, u16 zone,
>  {
>  	struct nf_conn *ct;
>  
> -	if (unlikely(!nf_conntrack_hash_rnd_initted)) {
> -		get_random_bytes(&nf_conntrack_hash_rnd,
> -				sizeof(nf_conntrack_hash_rnd));
> -		nf_conntrack_hash_rnd_initted = 1;
> +	if (unlikely(!nf_conntrack_hash_rnd)) {
> +		unsigned int rand;
> +
> +		/* Why not initialize nf_conntrack_rnd in a "init()" function ?
> +		 * Because there isn't enough entropy when system initializing,
> +		 * and we initialize it as late as possible. */

This patch is fine but a fine multi line comment is :
	/* Some
	 * fine
	 * comment
	 */

> +		do {
> +			get_random_bytes(&rand, sizeof(rand));
> +		} while (!rand);
> +		cmpxchg(&nf_conntrack_hash_rnd, 0, rand);
>  	}
>  
>  	/* We don't want any race condition at early drop stage */


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Re: [PATCH 1/2] netfilter: fix the hash random initializing race

[Jan Engelhardt]

On Friday 2010-08-20 18:17, Eric Dumazet wrote:
>> +	if (unlikely(!nf_conntrack_hash_rnd)) {
>> +		unsigned int rand;
>> +
>> +		/* Why not initialize nf_conntrack_rnd in a "init()" function ?
>> +		 * Because there isn't enough entropy when system initializing,
>> +		 * and we initialize it as late as possible. */
>
>This patch is fine but a fine multi line comment is :
>	/* Some
>	 * fine
>	 * comment
>	 */

Actually,

	/*
	 * Some
	 */

But that's in CodingStyle already. Always a good read, even if reread.

Re: [PATCH 1/2] netfilter: fix the hash random initializing race

[Eric Dumazet]

Le vendredi 20 août 2010 à 18:20 +0200, Jan Engelhardt a écrit :
> On Friday 2010-08-20 18:17, Eric Dumazet wrote:
> >> +	if (unlikely(!nf_conntrack_hash_rnd)) {
> >> +		unsigned int rand;
> >> +
> >> +		/* Why not initialize nf_conntrack_rnd in a "init()" function ?
> >> +		 * Because there isn't enough entropy when system initializing,
> >> +		 * and we initialize it as late as possible. */
> >
> >This patch is fine but a fine multi line comment is :
> >	/* Some
> >	 * fine
> >	 * comment
> >	 */
> 
> Actually,
> 
> 	/*
> 	 * Some
> 	 */
> 
> But that's in CodingStyle already. Always a good read, even if reread.

Sorry, I documented David S. Miller choice, or else I would have
mentioned CodingStyle :)

	/* Some
	 * fine
	 * comment
	 */

And it really is better ;)



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Re: [PATCH 1/2] netfilter: fix the hash random initializing race

[Jan Engelhardt]

On Friday 2010-08-20 18:26, Eric Dumazet wrote:

>> Actually,
>> 	/*
>> 	 * Some
>> 	 */
>> But that's in CodingStyle already. Always a good read, even if reread.
>
>Sorry, I documented David S. Miller choice, or else I would have
>mentioned CodingStyle :)
>
>	/* Some
>	 * fine
>	 * comment
>	 */
>
>And it really is better ;)

Looks unsymmetric, which is probably the reason CodingStyle was 
conceived differently in the first place.

Re: [PATCH 1/2] netfilter: fix the hash random initializing race

[Eric Dumazet]

Le vendredi 20 août 2010 à 18:34 +0200, Jan Engelhardt a écrit :
> On Friday 2010-08-20 18:26, Eric Dumazet wrote:
> 
> >> Actually,
> >> 	/*
> >> 	 * Some
> >> 	 */
> >> But that's in CodingStyle already. Always a good read, even if reread.
> >
> >Sorry, I documented David S. Miller choice, or else I would have
> >mentioned CodingStyle :)
> >
> >	/* Some
> >	 * fine
> >	 * comment
> >	 */
> >
> >And it really is better ;)
> 
> Looks unsymmetric, which is probably the reason CodingStyle was 
> conceived differently in the first place.

Who said comments must be symmetric ? :)

http://www.spinics.net/lists/netdev/msg134727.html



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Re: [PATCH 1/2] netfilter: fix the hash random initializing race

[Jan Engelhardt]

On Friday 2010-08-20 18:35, Eric Dumazet wrote:
>>>/* Some
>>> * fine
>>> * comment
>>> */
>>>And it really is better
>>Looks unsymmetric
>Who said comments must be symmetric ?

I can live with sub-level maintainers' free interpretation of areas
not covered by CodingStyle, but top-level maintainers directly going
against the law of Linux code is outrageous! The system is
undeniable :)