linux-kernel - Re: [PATCH] xsk: Add missing overflow check in xdp_umem

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Date:   Wed, 8 Mar 2023 16:33:46 +0100
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Kal Conley <kal.conley@...tris.com>
CC:     Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Jesper Dangaard Brouer" <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xsk: Add missing overflow check in xdp_umem_reg

From: Kal Conley <kal.conley@...tris.com>
Date: Wed,  8 Mar 2023 11:51:30 +0100

> [PATCH] xsk: Add missing overflow check in xdp_umem_reg

You need to mark it properly. It must've been

[PATCH bpf v2] xsk: Add missing overflow check in xdp_umem_reg

instead.

> The number of chunks can overflow u32. Make sure to return -EINVAL on
> overflow.

I'd mention here that cast removal, so that reviewers wouldn't ask why
you did this.

> 
> Fixes: bbff2f321a86 ("xsk: new descriptor addressing scheme")
> Signed-off-by: Kal Conley <kal.conley@...tris.com>
> ---
>  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;

The code is fine to me.
Please resubmit with the fixed subject and expanded commit message.
I'd also prefer that you sent v3 as a separate mail, *not* as a reply to
this thread.

Thanks,
Olek