Re: [PATCH v2 12/14] NTB: ntb_transport: Clear QP pointers when freeing an MW

[Logan Gunthorpe]

On 2026-09-09 22:08, Koichiro Den wrote:
> ntb_transport_link_cleanup() frees MW buffers but leaves rx_buff and
> remote_rx_info pointing into them. With a QP still allocated, another
> link-down notification or transport unbind before MW setup runs again
> can make ntb_qp_link_down_reset() write to freed memory through
> remote_rx_info.
> 
> Clear both pointers in ntb_free_mw() for all QPs using that MW,
> including those without a client. This also covers link-setup failures.
> 
> How to reproduce:
> 
>   1. Load ntb_transport and ntb_netdev on both sides and establish the
>      transport/QP links once. Stop traffic, but leave ntb_netdev loaded
>      on VHOST so its QPs remain allocated throughout the test.
> 
>   2. On HOST, unload ntb_netdev and ntb_transport, leaving ntb_hw_epf
>      bound:
> 
>      modprobe -r ntb_netdev ntb_transport
> 
>      Transport removal sends COMMAND_LINK_DOWN to VHOST. Wait for
>      ntb_transport_link_cleanup_work() to return on VHOST, using a
>      function-graph trace. The "Link Cleanup" message is printed before
>      MW release and is not sufficient to establish completion. Do not
>      bring the link back up before the next step.
> 
>   3-(A). UAF via repeated link-down notification
> 
>      Use ntb_tool on HOST to send another link-down request:
> 
>      HOST# modprobe ntb_tool
>      HOST# echo N > "/sys/kernel/debug/ntb_tool/$ntb_host_dev/link"
> 
>      ==================================================================
>      BUG: KASAN: vmalloc-out-of-bounds in ntb_qp_link_down_reset+0x2c0..
>      ...
>      Call trace:
>       ...
>       __asan_report_store4_noabort+0x1c/0x28
>       ntb_qp_link_down_reset+0x2c0/0x2e0 [ntb_transport]
>       ntb_qp_link_cleanup+0xc4/0x148 [ntb_transport]
>       ntb_transport_link_cleanup+0x314/0x350 [ntb_transport]
>       ntb_transport_link_cleanup_work+0x2c/0x50 [ntb_transport]
>       process_one_work+0x5b8/0x12f0
>       ...
> 
>   3-(B). UAF via transport removal after link-down
> 
>      VHOST# echo "$ntb_vhost_dev" > \
>          /sys/bus/ntb/drivers/ntb_transport/unbind
> 
>      ==================================================================
>      BUG: KASAN: vmalloc-out-of-bounds in ntb_qp_link_down_reset+0x2c0..
>      ...
>      Call trace:
>       ...
>       __asan_report_store4_noabort+0x1c/0x28
>       ntb_qp_link_down_reset+0x2c0/0x2e0 [ntb_transport]
>       ntb_qp_link_cleanup+0xc4/0x148 [ntb_transport]
>       ntb_transport_link_cleanup+0x314/0x350 [ntb_transport]
>       ntb_transport_free+0x68/0x588 [ntb_transport]
>       ntb_remove+0x5c/0xa0 [ntb]
> 
> Verified that neither test triggers a KASAN report with this patch.
> 
> Fixes: cc79bd2738c2 ("ntb: Clean up tx tail index on link down")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>

Makes sense to me:

Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>