Re: [PATCH bpf v3] xsk: Add missing overflow check in xdp_umem_reg

[Magnus Karlsson]

On Wed, 8 Mar 2023 at 18:51, Kal Conley <kal.conley@xxxxxxxxxxx> wrote:
>
> The number of chunks can overflow u32. Make sure to return -EINVAL on
> overflow.
>
> Also remove a redundant u32 cast assigning umem->npgs.

Thanks!

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

> Fixes: bbff2f321a86 ("xsk: new descriptor addressing scheme")
> Signed-off-by: Kal Conley <kal.conley@xxxxxxxxxxx>
> ---
>  net/xdp/xdp_umem.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> index 4681e8e8ad94..02207e852d79 100644
> --- a/net/xdp/xdp_umem.c
> +++ b/net/xdp/xdp_umem.c
> @@ -150,10 +150,11 @@ static int xdp_umem_account_pages(struct xdp_umem *umem)
>
>  static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
>  {
> -       u32 npgs_rem, chunk_size = mr->chunk_size, headroom = mr->headroom;
>         bool unaligned_chunks = mr->flags & XDP_UMEM_UNALIGNED_CHUNK_FLAG;
> -       u64 npgs, addr = mr->addr, size = mr->len;
> -       unsigned int chunks, chunks_rem;
> +       u32 chunk_size = mr->chunk_size, headroom = mr->headroom;
> +       u64 addr = mr->addr, size = mr->len;
> +       u32 chunks_rem, npgs_rem;
> +       u64 chunks, npgs;
>         int err;
>
>         if (chunk_size < XDP_UMEM_MIN_CHUNK_SIZE || chunk_size > PAGE_SIZE) {
> @@ -188,8 +189,8 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
>         if (npgs > U32_MAX)
>                 return -EINVAL;
>
> -       chunks = (unsigned int)div_u64_rem(size, chunk_size, &chunks_rem);
> -       if (chunks == 0)
> +       chunks = div_u64_rem(size, chunk_size, &chunks_rem);
> +       if (!chunks || chunks > U32_MAX)
>                 return -EINVAL;
>
>         if (!unaligned_chunks && chunks_rem)
> @@ -202,7 +203,7 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
>         umem->headroom = headroom;
>         umem->chunk_size = chunk_size;
>         umem->chunks = chunks;
> -       umem->npgs = (u32)npgs;
> +       umem->npgs = npgs;
>         umem->pgs = NULL;
>         umem->user = NULL;
>         umem->flags = mr->flags;
> --
> 2.39.2
>