Re: [PATCH] sched: address a potential NULL pointer dereference in the GRED scheduler.

[Cong Wang <xiyou.wangcong@gmail.com>]

On Tue, Mar 04, 2025 at 10:18:59PM +0800, kwqcheii wrote:
> If kzalloc in gred_init returns a NULL pointer, the code follows the error handling path,
> invoking gred_destroy. This, in turn, calls gred_offload, where memset could receive
> a NULL pointer as input, potentially leading to a kernel crash.
> 
> Signed-off-by: kwqcheii <juny24602@gmail.com>

Please use your real name for Signed-off-by.

> ---
>  net/sched/sch_gred.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sched/sch_gred.c b/net/sched/sch_gred.c
> index ab6234b4fcd5..fa643e5709bd 100644
> --- a/net/sched/sch_gred.c
> +++ b/net/sched/sch_gred.c
> @@ -317,10 +317,12 @@ static void gred_offload(struct Qdisc *sch, enum tc_gred_command command)
>  	if (!tc_can_offload(dev) || !dev->netdev_ops->ndo_setup_tc)
>  		return;
>  
> -	memset(opt, 0, sizeof(*opt));
> -	opt->command = command;
> -	opt->handle = sch->handle;
> -	opt->parent = sch->parent;
> +	if (opt) {
> +		memset(opt, 0, sizeof(*opt));
> +		opt->command = command;
> +		opt->handle = sch->handle;
> +		opt->parent = sch->parent;
> +	}

I think the whole gred_offload() should be skipped when table->opt ==
NULL, espeically the last call of ->ndo_setup_tc(). Something like:

diff --git a/net/sched/sch_gred.c b/net/sched/sch_gred.c
index ab6234b4fcd5..532fde548b88 100644
--- a/net/sched/sch_gred.c
+++ b/net/sched/sch_gred.c
@@ -913,7 +913,8 @@ static void gred_destroy(struct Qdisc *sch)
        for (i = 0; i < table->DPs; i++)
                gred_destroy_vq(table->tab[i]);

-       gred_offload(sch, TC_GRED_DESTROY);
+       if (table->opt)
+               gred_offload(sch, TC_GRED_DESTROY);
        kfree(table->opt);
 }

What do you think?

Thanks.