netdev - [PATCH] virtio_net: fix integer overflow in stats

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Message-ID: <53e2bd6728136d5916e384a7840e5dc7eebff832.1729099611.git.mst@redhat.com>
Date: Wed, 16 Oct 2024 13:27:07 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: "Colin King (gmail)" <colin.i.king@...il.com>,
	Jason Wang <jasowang@...hat.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: [PATCH] virtio_net: fix integer overflow in stats

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>
---
 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c6af18948092..b950d24b1ffa 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -4112,7 +4112,7 @@ struct virtnet_stats_ctx {
 	u32 desc_num[3];
 
 	/* The actual supported stat types. */
-	u32 bitmap[3];
+	u64 bitmap[3];
 
 	/* Used to calculate the reply buffer size. */
 	u32 size[3];
-- 
MST