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@xxxxxxxxx>
> ---
> 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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