Re: [PATCH] bpf: fix: address of local auto-variable assigned to a function parameter.

[Yonghong Song]

On 12/23/20 11:01 PM, YANG LI wrote:
> Assigning local variable txq to the outputting parameter xdp->txq is not
> safe, txq will be released after the end of the function call.
> Then the result of using xdp is unpredictable.
>
> Fix this error by defining the struct xdp_txq_info in function
> dev_map_run_prog() as a static type.
>
> Signed-off-by: YANG LI <abaci-bugfix@xxxxxxxxxxxxxxxxx>
> Reported-by: Abaci <abaci@xxxxxxxxxxxxxxxxx>
> ---
>   kernel/bpf/devmap.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index f6e9c68..af6f004 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -454,7 +454,7 @@ static struct xdp_buff *dev_map_run_prog(struct net_device *dev,
>   					 struct xdp_buff *xdp,
>   					 struct bpf_prog *xdp_prog)
>   {
> -	struct xdp_txq_info txq = { .dev = dev };
> +	static struct xdp_txq_info txq = { .dev = dev };
>   	u32 act;
>   
>   	xdp_set_data_meta_invalid(xdp);

exposing txq outside the routine with 'static' definition is not
a good practice. maybe just reset xdp->txq = NULl right before
function return?

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index f6e9c68afdd4..50f5c20a33a3 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -475,6 +475,7 @@ static struct xdp_buff *dev_map_run_prog(struct 
net_device *dev,
        }

        xdp_return_buff(xdp);
+       xdp->txq = NULL;
        return NULL;
 }

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