Re: [PATCH 4/6] netfilter: fix a race in nf_ct_ext_create()

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mercredi 22 septembre 2010 à 09:17 +0200, kaber@trash.net a écrit :
> From: Eric Dumazet <Eric Dumazet>
> 

strange email address ;)

> As soon as rcu_read_unlock() is called, there is no guarantee current
> thread can safely derefence t pointer, rcu protected.
> 
> Fix is to copy t->alloc_size in a temporary variable.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Patrick McHardy <kaber@trash.net>
> ---
>  net/netfilter/nf_conntrack_extend.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c
> index 7dcf7a4..8d9e4c9 100644
> --- a/net/netfilter/nf_conntrack_extend.c
> +++ b/net/netfilter/nf_conntrack_extend.c
> @@ -48,15 +48,17 @@ nf_ct_ext_create(struct nf_ct_ext **ext, enum nf_ct_ext_id id, gfp_t gfp)
>  {
>  	unsigned int off, len;
>  	struct nf_ct_ext_type *t;
> +	size_t alloc_size;
>  
>  	rcu_read_lock();
>  	t = rcu_dereference(nf_ct_ext_types[id]);
>  	BUG_ON(t == NULL);
>  	off = ALIGN(sizeof(struct nf_ct_ext), t->align);
>  	len = off + t->len;
> +	alloc_size = t->alloc_size;
>  	rcu_read_unlock();
>  
> -	*ext = kzalloc(t->alloc_size, gfp);
> +	*ext = kzalloc(alloc_size, gfp);
>  	if (!*ext)
>  		return NULL;
>  


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