netdev - Re: [PATCH bpf] xsk: fix corrupted packets for XDP_SHARED

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Date:   Fri, 12 Aug 2022 15:06:12 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Magnus Karlsson <magnus.karlsson@...il.com>
CC:     <magnus.karlsson@...el.com>, <bjorn@...nel.org>, <ast@...nel.org>,
        <daniel@...earbox.net>, <netdev@...r.kernel.org>,
        <jonathan.lemon@...il.com>, <bpf@...r.kernel.org>,
        Alasdair McWilliam <alasdair.mcwilliam@...look.com>,
        Intrusion Shield Team <dnevil@...rusion.com>
Subject: Re: [PATCH bpf] xsk: fix corrupted packets for XDP_SHARED_UMEM

On Fri, Aug 12, 2022 at 01:32:59PM +0200, Magnus Karlsson wrote:
> From: Magnus Karlsson <magnus.karlsson@...el.com>
> 
> Fix an issue in XDP_SHARED_UMEM mode together with aligned mode were

s/were/where

> packets are corrupted for the second and any further sockets bound to
> the same umem. In other words, this does not affect the first socket
> bound to the umem. The culprit for this bug is that the initialization
> of the DMA addresses for the pre-populated xsk buffer pool entries was
> not performed for any socket but the first one bound to the umem. Only
> the linear array of DMA addresses was populated. Fix this by
> populating the DMA addresses in the xsk buffer pool for every socket
> bound to the same umem.
> 
> Fixes: 94033cd8e73b8 ("xsk: Optimize for aligned case")
> Reported-by: Alasdair McWilliam <alasdair.mcwilliam@...look.com>
> Reported-by: Intrusion Shield Team <dnevil@...rusion.com>
> Tested-by: Alasdair McWilliam <alasdair.mcwilliam@...look.com>
> Link: https://lore.kernel.org/xdp-newbies/6205E10C-292E-4995-9D10-409649354226@outlook.com/
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> ---
>  net/xdp/xsk_buff_pool.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index f70112176b7c..a71a8c6edf55 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -379,6 +379,16 @@ static void xp_check_dma_contiguity(struct xsk_dma_map *dma_map)
>  
>  static int xp_init_dma_info(struct xsk_buff_pool *pool, struct xsk_dma_map *dma_map)
>  {
> +	if (!pool->unaligned) {
> +		u32 i;
> +
> +		for (i = 0; i < pool->heads_cnt; i++) {
> +			struct xdp_buff_xsk *xskb = &pool->heads[i];
> +
> +			xp_init_xskb_dma(xskb, pool, dma_map->dma_pages, xskb->orig_addr);

I wondered if it would be better to move it to the end of func and use
pool->dma_pages, but it probably doesn't matter in the end.

Great catch!
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>

> +		}
> +	}
> +
>  	pool->dma_pages = kvcalloc(dma_map->dma_pages_cnt, sizeof(*pool->dma_pages), GFP_KERNEL);
>  	if (!pool->dma_pages)
>  		return -ENOMEM;
> @@ -428,12 +438,6 @@ int xp_dma_map(struct xsk_buff_pool *pool, struct device *dev,
>  
>  	if (pool->unaligned)
>  		xp_check_dma_contiguity(dma_map);
> -	else
> -		for (i = 0; i < pool->heads_cnt; i++) {
> -			struct xdp_buff_xsk *xskb = &pool->heads[i];
> -
> -			xp_init_xskb_dma(xskb, pool, dma_map->dma_pages, xskb->orig_addr);
> -		}
>  
>  	err = xp_init_dma_info(pool, dma_map);
>  	if (err) {
> 
> base-commit: 4e4588f1c4d2e67c993208f0550ef3fae33abce4
> -- 
> 2.34.1
>