Re: [PATCH net] virtio-net: free xsk_buffs on error in virtnet_xsk_pool_enable()

[Simon Horman <horms@kernel.org>]

On Tue, Apr 29, 2025 at 09:43:23AM -0700, Jakub Kicinski wrote:
> The selftests added to our CI by Bui Quang Minh recently reveals
> that there is a mem leak on the error path of virtnet_xsk_pool_enable():
> 
> unreferenced object 0xffff88800a68a000 (size 2048):
>   comm "xdp_helper", pid 318, jiffies 4294692778
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace (crc 0):
>     __kvmalloc_node_noprof+0x402/0x570
>     virtnet_xsk_pool_enable+0x293/0x6a0 (drivers/net/virtio_net.c:5882)
>     xp_assign_dev+0x369/0x670 (net/xdp/xsk_buff_pool.c:226)
>     xsk_bind+0x6a5/0x1ae0
>     __sys_bind+0x15e/0x230
>     __x64_sys_bind+0x72/0xb0
>     do_syscall_64+0xc1/0x1d0
>     entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Fixes: e9f3962441c0 ("virtio_net: xsk: rx: support fill with xsk buffer")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> CC: mst@redhat.com
> CC: jasowang@redhat.com
> CC: xuanzhuo@linux.alibaba.com
> CC: eperezma@redhat.com
> CC: hawk@kernel.org
> CC: john.fastabend@gmail.com
> CC: virtualization@lists.linux.dev
> CC: minhquangbui99@gmail.com
> ---
>  drivers/net/virtio_net.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 848fab51dfa1..a3d4e666c2a0 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -5886,7 +5886,7 @@ static int virtnet_xsk_pool_enable(struct net_device *dev,
>  	hdr_dma = virtqueue_dma_map_single_attrs(sq->vq, &xsk_hdr, vi->hdr_len,
>  						 DMA_TO_DEVICE, 0);
>  	if (virtqueue_dma_mapping_error(sq->vq, hdr_dma))
> -		return -ENOMEM;

Hi Jakub,

I think you need the following here:

		err = -ENOMEM;

Else err is uninitialised when jumping to the err_free_buffs label.

Flagged by clang 20.1.3 [-Wsometimes-uninitialized], and Smatch.

> +		goto err_free_buffs;
>  
>  	err = xsk_pool_dma_map(pool, dma_dev, 0);
>  	if (err)
> @@ -5914,6 +5914,8 @@ static int virtnet_xsk_pool_enable(struct net_device *dev,
>  err_xsk_map:
>  	virtqueue_dma_unmap_single_attrs(rq->vq, hdr_dma, vi->hdr_len,
>  					 DMA_TO_DEVICE, 0);
> +err_free_buffs:
> +	kvfree(rq->xsk_buffs);
>  	return err;
>  }
>  
> -- 
> 2.49.0
>