RE: [PATCH bpf 2/3] bpf, sockhash: synchronize_rcu before free'ing map

[John Fastabend <john.fastabend@gmail.com>]

Jakub Sitnicki wrote:
> We need to have a synchronize_rcu before free'ing the sockhash because any
> outstanding psock references will have a pointer to the map and when they
> use it, this could trigger a use after free.
> 
> This is a sister fix for sockhash, following commit 2bb90e5cc90e ("bpf:
> sockmap, synchronize_rcu before free'ing map") which addressed sockmap,
> which comes from a manual audit.
> 
> Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
> ---
>  net/core/sock_map.c | 4 ++++
>  1 file changed, 4 insertions(+)

Nice catch thanks. As far as I know I've never seen this happen but
lets get this fixed.

Acked-by: John Fastabend <john.fastabend@gmail.com>

> 
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index fd8b426dbdf3..f36e13e577a3 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -250,6 +250,7 @@ static void sock_map_free(struct bpf_map *map)
>  	}
>  	raw_spin_unlock_bh(&stab->lock);
>  
> +	/* wait for psock readers accessing its map link */
>  	synchronize_rcu();
>  
>  	bpf_map_area_free(stab->sks);
> @@ -873,6 +874,9 @@ static void sock_hash_free(struct bpf_map *map)
>  		raw_spin_unlock_bh(&bucket->lock);
>  	}
>  
> +	/* wait for psock readers accessing its map link */
> +	synchronize_rcu();
> +
>  	bpf_map_area_free(htab->buckets);
>  	kfree(htab);
>  }
> -- 
> 2.24.1
>