Commit 7625645e authored by Amery Hung's avatar Amery Hung Committed by Martin KaFai Lau
Browse files

bpf: net_sched: Fix using bpf qdisc as default qdisc 



Use bpf_try_module_get()/bpf_module_put() instead of try_module_get()/
module_put() when handling default qdisc since users can assign a bpf
qdisc to it.

To trigger the bug:
$ bpftool struct_ops register bpf_qdisc_fq.bpf.o /sys/fs/bpf
$ echo bpf_fq > /proc/sys/net/core/default_qdisc

Fixes: c8240344 ("bpf: net_sched: Support implementation of Qdisc_ops in bpf")
Signed-off-by: default avatarAmery Hung <ameryhung@gmail.com>
Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250429192128.3860571-1-ameryhung@gmail.com
parent 1ce65102

net/sched/sch_api.c

+2 −2
Original line number Diff line number Diff line
@@ -208,7 +208,7 @@ static struct Qdisc_ops *qdisc_lookup_default(const char *name) 


	for (q = qdisc_base; q; q = q->next) {

		if (!strcmp(name, q->id)) {

			if (!try_module_get(q->owner))

			if (!bpf_try_module_get(q, q->owner))

				q = NULL;

			break;

		}
@@ -238,7 +238,7 @@ int qdisc_set_default(const char *name) 


	if (ops) {

		/* Set new default */

		module_put(default_qdisc_ops->owner);

		bpf_module_put(default_qdisc_ops, default_qdisc_ops->owner);

		default_qdisc_ops = ops;

	}

	write_unlock(&qdisc_mod_lock);

net/sched/sch_generic.c

+2 −2
Original line number Diff line number Diff line
@@ -1002,14 +1002,14 @@ struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue, 
{

	struct Qdisc *sch;



	if (!try_module_get(ops->owner)) {

	if (!bpf_try_module_get(ops, ops->owner)) {

		NL_SET_ERR_MSG(extack, "Failed to increase module reference counter");

		return NULL;

	}



	sch = qdisc_alloc(dev_queue, ops, extack);

	if (IS_ERR(sch)) {

		module_put(ops->owner);

		bpf_module_put(ops, ops->owner);

		return NULL;

	}

	sch->parent = parentid;