Re: [PATCH net v1 1/4] net: devmem: unmap dma_buf synchronously on queue uninstall

[Pavel Begunkov <asml.silence@gmail.com>]

On 10/10/26 03:55, Mina Almasry wrote:
> When a bound net_device is unregistered while userspace still holds a
> netlink or TCP socket reference on a devmem binding,
> mp_dmabuf_devmem_uninstall() clears binding->dev to NULL so
> netdev_nl_sock_priv_destroy() will not touch the unregistered
> net_device, but leaves the dma_buf attachment mapped until
> __net_devmem_dmabuf_binding_free() runs later on socket close.
> 
> Because dma_buf_attach() does not take a reference on dma_dev, device
> removal frees dma_dev while the attachment is still mapped. Closing the
> netlink socket afterwards triggers a slab use-after-free in
> dma_unmap_sg_attrs():
> 
>    BUG: KASAN: slab-use-after-free in dma_unmap_sg_attrs+0x76/0x2b0
>    Read of size 8 at addr ffff88810fae64b0 by task kworker/3:1/53
>    Workqueue: events __net_devmem_dmabuf_binding_free
>    Call Trace:
>     dma_unmap_sg_attrs+0x76/0x2b0
>     unmap_udmabuf+0x8e/0x100
>     dma_buf_unmap_attachment+0x145/0x330
>     dma_buf_unmap_attachment_unlocked+0x96/0x130
>     __net_devmem_dmabuf_binding_free+0x156/0x2e0
>    Freed by task 9:
>     kfree+0x1b8/0x550
>     nsim_bus_dev_release+0xe/0x60
>     device_release+0xcf/0x250
> 
> Add net_devmem_dmabuf_binding_unmap() serialized under binding->lock
> and null out binding->sgt and binding->attachment after unmapping so
> unmapping is idempotent across queue uninstall and deferred binding
> destruction. Call it synchronously when the last bound RX queue is
> uninstalled in mp_dmabuf_devmem_uninstall().
> 
> Fixes: f8350a4358fc ("net: page_pool: add a mp hook to unregister_netdevice*")

It looks more like 170aafe35cb98e0f3fbacb446ea86389fbce22ea
("netdev: support binding dma-buf to netdevice"). The one in the
tag didn't do anything interesting.

The fix looks good as well, might be a good idea to clear
net_iov's dma_addr as well.

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>

-- 
Pavel Begunkov