linux-kernel - Re: [PATCH] virtio_net: fix integer overflow in stats

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Message-ID: <CACGkMEsovgv9=jj76dfATHWHY7c6NAmiqKDaARDGYju-A6zaKg@mail.gmail.com>
Date: Thu, 17 Oct 2024 14:51:06 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org, 
	"Colin King (gmail)" <colin.i.king@...il.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Eugenio Pérez <eperezma@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, virtualization@...ts.linux.dev, 
	netdev@...r.kernel.org
Subject: Re: [PATCH] virtio_net: fix integer overflow in stats

On Thu, Oct 17, 2024 at 1:27 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> Static analysis on linux-next has detected the following issue
> in function virtnet_stats_ctx_init, in drivers/net/virtio_net.c :
>
>         if (vi->device_stats_cap & VIRTIO_NET_STATS_TYPE_CVQ) {
>                 queue_type = VIRTNET_Q_TYPE_CQ;
>                 ctx->bitmap[queue_type]   |= VIRTIO_NET_STATS_TYPE_CVQ;
>                 ctx->desc_num[queue_type] += ARRAY_SIZE(virtnet_stats_cvq_desc);
>                 ctx->size[queue_type]     += sizeof(struct virtio_net_stats_cvq);
>         }
>
> ctx->bitmap is declared as a u32 however it is being bit-wise or'd with
> VIRTIO_NET_STATS_TYPE_CVQ and this is defined as 1 << 32:
>
> include/uapi/linux/virtio_net.h:#define VIRTIO_NET_STATS_TYPE_CVQ (1ULL << 32)
>
> ..and hence the bit-wise or operation won't set any bits in ctx->bitmap
> because 1ULL < 32 is too wide for a u32.
>
> In fact, the field is read into a u64:
>
>        u64 offset, bitmap;
> ....
>        bitmap = ctx->bitmap[queue_type];
>
> so to fix, it is enough to make bitmap an array of u64.
>
> Fixes: 941168f8b40e5 ("virtio_net: support device stats")
> Reported-by: "Colin King (gmail)" <colin.i.king@...il.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---

Acked-by: Jason Wang <jasowang@...hat.com>

Thanks