Re: [PATCH v3 net] net: Fix an unsafe loop on the list

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Anastasia Kovaleva <a.kovaleva@yadro.com>
Date: Thu, 3 Oct 2024 13:44:31 +0300
> The kernel may crash when deleting a genetlink family if there are still
> listeners for that family:
> 
> Oops: Kernel access of bad area, sig: 11 [#1]
>   ...
>   NIP [c000000000c080bc] netlink_update_socket_mc+0x3c/0xc0
>   LR [c000000000c0f764] __netlink_clear_multicast_users+0x74/0xc0
>   Call Trace:
> __netlink_clear_multicast_users+0x74/0xc0
> genl_unregister_family+0xd4/0x2d0
> 
> Change the unsafe loop on the list to a safe one, because inside the
> loop there is an element removal from this list.
> 
> Fixes: b8273570f802 ("genetlink: fix netns vs. netlink table locking (2)")
> Cc: stable@vger.kernel.org
> Signed-off-by: Anastasia Kovaleva <a.kovaleva@yadro.com>
> Reviewed-by: Dmitry Bogdanov <d.bogdanov@yadro.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>


> ---
> v3: remove trailing "\", change spaces to tab
> v2: add CC tag for stable
> ---
>  include/net/sock.h       | 2 ++
>  net/netlink/af_netlink.c | 3 ++-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index c58ca8dd561b..db29c39e19a7 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -894,6 +894,8 @@ static inline void sk_add_bind_node(struct sock *sk,
>  	hlist_for_each_entry_safe(__sk, tmp, list, sk_node)
>  #define sk_for_each_bound(__sk, list) \
>  	hlist_for_each_entry(__sk, list, sk_bind_node)
> +#define sk_for_each_bound_safe(__sk, tmp, list) \
> +	hlist_for_each_entry_safe(__sk, tmp, list, sk_bind_node)
>  
>  /**
>   * sk_for_each_entry_offset_rcu - iterate over a list at a given struct offset
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index 0b7a89db3ab7..0a9287fadb47 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -2136,8 +2136,9 @@ void __netlink_clear_multicast_users(struct sock *ksk, unsigned int group)
>  {
>  	struct sock *sk;
>  	struct netlink_table *tbl = &nl_table[ksk->sk_protocol];
> +	struct hlist_node *tmp;
>  
> -	sk_for_each_bound(sk, &tbl->mc_list)
> +	sk_for_each_bound_safe(sk, tmp, &tbl->mc_list)
>  		netlink_update_socket_mc(nlk_sk(sk), group, 0);
>  }
>  
> -- 
> 2.40.1