netdev - Re: [PATCH net] net: psample: Fix the netlink skb length

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Message-ID: <20210203182103.0f8350a9@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 3 Feb 2021 18:21:03 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Chris Mi <cmi@...dia.com>
Cc:     netdev@...r.kernel.org, idosch@...dia.com,
        Yotam Gigi <yotam.gi@...il.com>
Subject: Re: [PATCH net] net: psample: Fix the netlink skb length

On Wed,  3 Feb 2021 11:10:28 +0800 Chris Mi wrote:
> Currently, the netlink skb length only includes metadata and data
> length. It doesn't include the psample generic netlink header length.

But what's the bug? Did you see oversized messages on the socket? Did
one of the nla_put() fail?

> Fixes: 6ae0a6286171 ("net: Introduce psample, a new genetlink channel for packet sampling")
> CC: Yotam Gigi <yotam.gi@...il.com>
> Reviewed-by: Ido Schimmel <idosch@...dia.com>
> Signed-off-by: Chris Mi <cmi@...dia.com>
> ---
>  net/psample/psample.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/net/psample/psample.c b/net/psample/psample.c
> index 33e238c965bd..807d75f5a40f 100644
> --- a/net/psample/psample.c
> +++ b/net/psample/psample.c
> @@ -363,6 +363,7 @@ void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
>  	struct ip_tunnel_info *tun_info;
>  #endif
>  	struct sk_buff *nl_skb;
> +	int header_len;
>  	int data_len;
>  	int meta_len;
>  	void *data;
> @@ -381,12 +382,13 @@ void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
>  		meta_len += psample_tunnel_meta_len(tun_info);
>  #endif
>  
> +	/* psample generic netlink header size */
> +	header_len = nlmsg_total_size(GENL_HDRLEN + psample_nl_family.hdrsize);

GENL_HDRLEN is already included by genlmsg_new() and fam->hdrsize is 0
/ uninitialized for psample_nl_family. What am I missing? Ido?

>  	data_len = min(skb->len, trunc_size);
> -	if (meta_len + nla_total_size(data_len) > PSAMPLE_MAX_PACKET_SIZE)
> -		data_len = PSAMPLE_MAX_PACKET_SIZE - meta_len - NLA_HDRLEN
> +	if (header_len + meta_len + nla_total_size(data_len) > PSAMPLE_MAX_PACKET_SIZE)
> +		data_len = PSAMPLE_MAX_PACKET_SIZE - header_len - meta_len - NLA_HDRLEN
>  			    - NLA_ALIGNTO;
> -
> -	nl_skb = genlmsg_new(meta_len + nla_total_size(data_len), GFP_ATOMIC);
> +	nl_skb = genlmsg_new(header_len + meta_len + nla_total_size(data_len), GFP_ATOMIC);
>  	if (unlikely(!nl_skb))
>  		return;
>