Re: [PATCH bpf] xsk: Fix unaligned descriptor validation

[Magnus Karlsson]

On Mon, 3 Apr 2023 at 16:38, Kal Conley <kal.conley@xxxxxxxxxxx> wrote:
>
> Make sure unaligned descriptors that straddle the end of the UMEM are
> considered invalid. Currently, descriptor validation is broken for
> zero-copy mode which only checks descriptors at page granularity.
> Descriptors that cross the end of the UMEM but not a page boundary may
> be therefore incorrectly considered valid. The check needs to happen
> before the page boundary and contiguity checks in
> xp_desc_crosses_non_contig_pg. Do this check in
> xp_unaligned_validate_desc instead like xp_check_unaligned already does.

Thanks for catching this Kal.

Acked-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>

> Fixes: 2b43470add8c ("xsk: Introduce AF_XDP buffer allocation API")
> Signed-off-by: Kal Conley <kal.conley@xxxxxxxxxxx>
> ---
>  include/net/xsk_buff_pool.h | 9 ++-------
>  net/xdp/xsk_queue.h         | 1 +
>  2 files changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
> index 3e952e569418..d318c769b445 100644
> --- a/include/net/xsk_buff_pool.h
> +++ b/include/net/xsk_buff_pool.h
> @@ -180,13 +180,8 @@ static inline bool xp_desc_crosses_non_contig_pg(struct xsk_buff_pool *pool,
>         if (likely(!cross_pg))
>                 return false;
>
> -       if (pool->dma_pages_cnt) {
> -               return !(pool->dma_pages[addr >> PAGE_SHIFT] &
> -                        XSK_NEXT_PG_CONTIG_MASK);
> -       }
> -
> -       /* skb path */
> -       return addr + len > pool->addrs_cnt;
> +       return pool->dma_pages_cnt &&
> +              !(pool->dma_pages[addr >> PAGE_SHIFT] & XSK_NEXT_PG_CONTIG_MASK);
>  }
>
>  static inline u64 xp_aligned_extract_addr(struct xsk_buff_pool *pool, u64 addr)
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index bfb2a7e50c26..66c6f57c9c44 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -162,6 +162,7 @@ static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
>                 return false;
>
>         if (base_addr >= pool->addrs_cnt || addr >= pool->addrs_cnt ||
> +           addr + desc->len > pool->addrs_cnt ||
>             xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
>                 return false;
>
> --
> 2.39.2
>