Re: [PATCH] net: sched: fix memory leak in tcindex_set_parms

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 31 Oct 2022 14:08:35 +0800 Hawkins Jiawei wrote:
> Kernel will uses tcindex_change() to change an existing

s/will//

> traffic-control-indices filter properties. During the
> process of changing, kernel will clears the old

s/will//

> traffic-control-indices filter result, and updates it
> by RCU assigning new traffic-control-indices data.
> 
> Yet the problem is that, kernel will clears the old

s/will//

> traffic-control-indices filter result, without destroying
> its tcf_exts structure, which triggers the above
> memory leak.
> 
> This patch solves it by using tcf_exts_destroy() to
> destroy the tcf_exts structure in old
> traffic-control-indices filter result.
> 

Please provide a Fixes tag to where the problem was introduced 
(or the initial git commit).

> Link: https://lore.kernel.org/all/0000000000001de5c505ebc9ec59@google.com/
> Reported-by: syzbot+232ebdbd36706c965ebf@syzkaller.appspotmail.com
> Tested-by: syzbot+232ebdbd36706c965ebf@syzkaller.appspotmail.com
> Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
> ---
>  net/sched/cls_tcindex.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
> index 1c9eeb98d826..dc872a794337 100644
> --- a/net/sched/cls_tcindex.c
> +++ b/net/sched/cls_tcindex.c
> @@ -338,6 +338,9 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
>  	struct tcf_result cr = {};
>  	int err, balloc = 0;
>  	struct tcf_exts e;
> +#ifdef CONFIG_NET_CLS_ACT
> +	struct tcf_exts old_e = {};
> +#endif

Why all the ifdefs?

>  	err = tcf_exts_init(&e, net, TCA_TCINDEX_ACT, TCA_TCINDEX_POLICE);
>  	if (err < 0)
> @@ -479,6 +482,14 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
>  	}
>  
>  	if (old_r && old_r != r) {
> +#ifdef CONFIG_NET_CLS_ACT
> +		/* r->exts is not copied from old_r->exts, and
> +		 * the following code will clears the old_r, so
> +		 * we need to destroy it after updating the tp->root,
> +		 * to avoid memory leak bug.
> +		 */
> +		old_e = old_r->exts;
> +#endif

Can't you localize all the changes to this if block?

Maybe add a function called tcindex_filter_result_reinit()
which will act more appropriately?

>  		err = tcindex_filter_result_init(old_r, cp, net);
>  		if (err < 0) {
>  			kfree(f);
> @@ -510,6 +521,9 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
>  		tcf_exts_destroy(&new_filter_result.exts);
>  	}
>  
> +#ifdef CONFIG_NET_CLS_ACT
> +	tcf_exts_destroy(&old_e);
> +#endif
>  	if (oldp)
>  		tcf_queue_work(&oldp->rwork, tcindex_partial_destroy_work);
>  	return 0;