Re: [PATCH net-next] net: Prevent use after free in netif_napi_set_irq_locked()

[Ahmed Zaki <ahmed.zaki@intel.com>]

On 2025-03-03 5:02 a.m., Dan Carpenter wrote:
> The cpu_rmap_put() will call kfree() when the last reference is dropped
> so it could result in a use after free when we dereference the same
> pointer the next line.  Move the cpu_rmap_put() after the dereference.

The last call to cpu_rmap_put() that frees the rmap will always be in 
netif_del_cpu_rmap(). This matches the ref counter  initially set in 
netif_enable_cpu_rmap().



> 
> Fixes: bd7c00605ee0 ("net: move aRFS rmap management and CPU affinity to core")
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> ---
>   net/core/dev.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 9189c4a048d7..c102349e04ee 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -7072,8 +7072,8 @@ void netif_napi_set_irq_locked(struct napi_struct *napi, int irq)
>   put_rmap:
>   #ifdef CONFIG_RFS_ACCEL
>   	if (napi->dev->rx_cpu_rmap_auto) {
> -		cpu_rmap_put(napi->dev->rx_cpu_rmap);
>   		napi->dev->rx_cpu_rmap->obj[napi->napi_rmap_idx] = NULL;
> +		cpu_rmap_put(napi->dev->rx_cpu_rmap);
>   		napi->napi_rmap_idx = -1;
>   	}
>   #endif