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SubjectRe: [PATCH] net: sched: fix memory leak in tcindex_set_parms
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;

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