Re: [PATCH net-next v4 05/12] net: rtnetlink: add bulk delete support flag

[Ido Schimmel <idosch@idosch.org>]

On Wed, Apr 13, 2022 at 01:51:55PM +0300, Nikolay Aleksandrov wrote:
> Add a new rtnl flag (RTNL_FLAG_BULK_DEL_SUPPORTED) which is used to
> verify that the delete operation allows bulk object deletion. Also emit
> a warning if anyone tries to set it for non-delete kind.
> 
> Suggested-by: David Ahern <dsahern@kernel.org>
> Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
> ---
> v4: new patch
> 
>  include/net/rtnetlink.h | 3 ++-
>  net/core/rtnetlink.c    | 8 ++++++++
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
> index 0bf622409aaa..bf8bb3357825 100644
> --- a/include/net/rtnetlink.h
> +++ b/include/net/rtnetlink.h
> @@ -10,7 +10,8 @@ typedef int (*rtnl_doit_func)(struct sk_buff *, struct nlmsghdr *,
>  typedef int (*rtnl_dumpit_func)(struct sk_buff *, struct netlink_callback *);
>  
>  enum rtnl_link_flags {
> -	RTNL_FLAG_DOIT_UNLOCKED = BIT(0),
> +	RTNL_FLAG_DOIT_UNLOCKED		= BIT(0),
> +	RTNL_FLAG_BULK_DEL_SUPPORTED	= BIT(1),
>  };
>  
>  enum rtnl_kinds {
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index beda4a7da062..63c7df52a667 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -249,6 +249,8 @@ static int rtnl_register_internal(struct module *owner,
>  	if (dumpit)
>  		link->dumpit = dumpit;
>  
> +	WARN_ON(rtnl_msgtype_kind(msgtype) != RTNL_KIND_DEL &&
> +		(flags & RTNL_FLAG_BULK_DEL_SUPPORTED));
>  	link->flags |= flags;
>  
>  	/* publish protocol:msgtype */
> @@ -6009,6 +6011,12 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
>  	}
>  
>  	flags = link->flags;
> +	if (kind == RTNL_KIND_DEL && (nlh->nlmsg_flags & NLM_F_BULK) &&
> +	    !(flags & RTNL_FLAG_BULK_DEL_SUPPORTED)) {
> +		NL_SET_ERR_MSG(extack, "Bulk delete is not supported");
> +		goto err_unlock;

If a buggy user space application is sending messages with NLM_F_BULK
set (unintentionally), will it break on newer kernel? I couldn't find
where the kernel was validating that reserved flags are not used (I
suspect it doesn't).

Assuming the above is correct and of interest, maybe just emit a warning
via extack and drop the goto? Alternatively, we can see if anyone
complains which might never happen

> +	}
> +
>  	if (flags & RTNL_FLAG_DOIT_UNLOCKED) {
>  		doit = link->doit;
>  		rcu_read_unlock();
> -- 
> 2.35.1
>