[PATCH 6.18 149/212] net/sched: teql: Fix double-free in teql_master_xmit

Greg Kroah-Hartman
2026-03-23T14:08:19Z

From: Jamal Hadi Salim <jhs@mojatatu.com>

[ Upstream commit 66360460cab63c248ca5b1070a01c0c29133b960 ]

Whenever a TEQL devices has a lockless Qdisc as root, qdisc_reset should
be called using the seq_lock to avoid racing with the datapath. Failure
to do so may cause crashes like the following:

[ 238.028993][ T318] BUG: KASAN: double-free in skb_release_data (net/core/skbuff.c:1139)
[ 238.029328][ T318] Free of addr ffff88810c67ec00 by task poc_teql_uaf_ke/318
[ 238.029749][ T318]
[ 238.029900][ T318] CPU: 3 UID: 0 PID: 318 Comm: poc_teql_ke Not tainted 7.0.0-rc3-00149-ge5b31d988a41 #704 PREEMPT(full)
[ 238.029906][ T318] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 238.029910][ T318] Call Trace:
[ 238.029913][ T318] <TASK>
[ 238.029916][ T318] dump_stack_lvl (lib/dump_stack.c:122)
[ 238.029928][ T318] print_report (mm/kasan/report.c:379 mm/kasan/report.c:482)
[ 238.029940][ T318] ? skb_release_data (net/core/skbuff.c:1139)
[ 238.029944][ T318] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
...
[ 238.029957][ T318] ? skb_release_data (net/core/skbuff.c:1139)
[ 238.029969][ T318] kasan_report_invalid_free (mm/kasan/report.c:221 mm/kasan/report.c:563)
[ 238.029979][ T318] ? skb_release_data (net/core/skbuff.c:1139)
[ 238.029989][ T318] check_slab_allocation (mm/kasan/common.c:231)
[ 238.029995][ T318] kmem_cache_free (mm/slub.c:2637 (discriminator 1) mm/slub.c:6168 (discriminator 1) mm/slub.c:6298 (discriminator 1))
[ 238.030004][ T318] skb_release_data (net/core/skbuff.c:1139)
...
[ 238.030025][ T318] sk_skb_reason_drop (net/core/skbuff.c:1256)
[ 238.030032][ T318] pfifo_fast_reset (./include/linux/ptr_ring.h:171 ./include/linux/ptr_ring.h:309 ./include/linux/skb_array.h:98 net/sched/sch_generic.c:827)
[ 238.030039][ T318] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
...
[ 238.030054][ T318] qdisc_reset (net/sched/sch_generic.c:1034)
[ 238.030062][ T318] teql_destroy (./include/linux/spinlock.h:395 net/sched/sch_teql.c:157)
[ 238.030071][ T318] __qdisc_destroy (./include/net/pkt_sched.h:328 net/sched/sch_generic.c:1077)
[ 238.030077][ T318] qdisc_graft (net/sched/sch_api.c:1062 net/sched/sch_api.c:1053 net/sched/sch_api.c:1159)
[ 238.030089][ T318] ? __pfx_qdisc_graft (net/sched/sch_api.c:1091)
[ 238.030095][ T318] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[ 238.030102][ T318] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[ 238.030106][ T318] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:221)
[ 238.030114][ T318] tc_get_qdisc (net/sched/sch_api.c:1529 net/sched/sch_api.c:1556)
...
[ 238.072958][ T318] Allocated by task 303 on cpu 5 at 238.026275s:
[ 238.073392][ T318] kasan_save_stack (mm/kasan/common.c:58)
[ 238.073884][ T318] kasan_save_track (mm/kasan/common.c:64 (discriminator 5) mm/kasan/common.c:79 (discriminator 5))
[ 238.074230][ T318] __kasan_slab_alloc (mm/kasan/common.c:369)
[ 238.074578][ T318] kmem_cache_alloc_node_noprof (./include/linux/kasan.h:253 mm/slub.c:4542 mm/slub.c:4869 mm/slub.c:4921)
[ 238.076091][ T318] kmalloc_reserve (net/core/skbuff.c:616 (discriminator 107))
[ 238.076450][ T318] __alloc_skb (net/core/skbuff.c:713)
[ 238.076834][ T318] alloc_skb_with_frags (./include/linux/skbuff.h:1383 net/core/skbuff.c:6763)
[ 238.077178][ T318] sock_alloc_send_pskb (net/core/sock.c:2997)
[ 238.077520][ T318] packet_sendmsg (net/packet/af_packet.c:2926 net/packet/af_packet.c:3019 net/packet/af_packet.c:3108)
[ 238.081469][ T318]
[ 238.081870][ T318] Freed by task 299 on cpu 1 at 238.028496s:
[ 238.082761][ T318] kasan_save_stack (mm/kasan/common.c:58)
[ 238.083481][ T318] kasan_save_track (mm/kasan/common.c:64 (discriminator 5) mm/kasan/common.c:79 (discriminator 5))
[ 238.085348][ T318] kasan_save_free_info (mm/kasan/generic.c:587 (discriminator 1))
[ 238.085900][ T318] __kasan_slab_free (mm/kasan/common.c:287)
[ 238.086439][ T318] kmem_cache_free (mm/slub.c:6168 (discriminator 3) mm/slub.c:6298 (discriminator 3))
[ 238.087007][ T318] skb_release_data (net/core/skbuff.c:1139)
[ 238.087491][ T318] consume_skb (net/core/skbuff.c:1451)
[ 238.087757][ T318] teql_master_xmit (net/sched/sch_teql.c:358)
[ 238.088116][ T318] dev_hard_start_xmit (./include/linux/netdevice.h:5324 ./include/linux/netdevice.h:5333 net/core/dev.c:3871 net/core/dev.c:3887)
[ 238.088468][ T318] sch_direct_xmit (net/sched/sch_generic.c:347)
[ 238.088820][ T318] __qdisc_run (net/sched/sch_generic.c:420 (discriminator 1))
[ 238.089166][ T318] __dev_queue_xmit (./include/net/sch_generic.h:229 ./include/net/pkt_sched.h:121 ./include/net/pkt_sched.h:117 net/core/dev.c:4196 net/core/dev.c:4802)

Workflow to reproduce:
1. Initialize a TEQL topology (dummy0 and ifb0 as slaves, teql0 up).
2. Start multiple sender workers continuously transmitting packets
through teql0 to drive teql_master_xmit().
3. In parallel, repeatedly delete and re-add the root qdisc on
dummy0 and ifb0 via RTNETLINK, forcing frequent teardown and reset activity
(teql_destroy() / qdisc_reset()).
4. After running both workloads concurrently for several iterations,
KASAN reports slab-use-after-free or double-free in the skb free path.

Fix this by moving dev_reset_queue to sch_generic.h and calling it, instead
of qdisc_reset, in teql_destroy since it handles both the lock and lockless
cases correctly for root qdiscs.

Fixes: 96009c7d500e ("sched: replace __QDISC_STATE_RUNNING bit with a spin lock")
Reported-by: Xianrui Dong <keenanat2000@gmail.com>
Tested-by: Xianrui Dong <keenanat2000@gmail.com>
Co-developed-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20260315155422.147256-1-jhs@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/sch_generic.h | 28 ++++++++++++++++++++++++++++
net/sched/sch_generic.c | 27 ---------------------------
net/sched/sch_teql.c | 7 ++-----
3 files changed, 30 insertions(+), 32 deletions(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 1518454c906e1..84c86decebdfa 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -696,6 +696,34 @@ void qdisc_destroy(struct Qdisc *qdisc);
void qdisc_put(struct Qdisc *qdisc);
void qdisc_put_unlocked(struct Qdisc *qdisc);
void qdisc_tree_reduce_backlog(struct Qdisc *qdisc, int n, int len);
+
+static inline void dev_reset_queue(struct net_device *dev,
+ struct netdev_queue *dev_queue,
+ void *_unused)
+{
+ struct Qdisc *qdisc;
+ bool nolock;
+
+ qdisc = rtnl_dereference(dev_queue->qdisc_sleeping);
+ if (!qdisc)
+ return;
+
+ nolock = qdisc->flags & TCQ_F_NOLOCK;
+
+ if (nolock)
+ spin_lock_bh(&qdisc->seqlock);
+ spin_lock_bh(qdisc_lock(qdisc));
+
+ qdisc_reset(qdisc);
+
+ spin_unlock_bh(qdisc_lock(qdisc));
+ if (nolock) {
+ clear_bit(__QDISC_STATE_MISSED, &qdisc->state);
+ clear_bit(__QDISC_STATE_DRAINING, &qdisc->state);
+ spin_unlock_bh(&qdisc->seqlock);
+ }
+}
+
#ifdef CONFIG_NET_SCHED
int qdisc_offload_dump_helper(struct Qdisc *q, enum tc_setup_type type,
void *type_data);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 7dee9748a56be..30d77ad7b81d2 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1297,33 +1297,6 @@ static void dev_deactivate_queue(struct net_device *dev,
}
}

-static void dev_reset_queue(struct net_device *dev,
- struct netdev_queue *dev_queue,
- void *_unused)
-{
- struct Qdisc *qdisc;
- bool nolock;
-
- qdisc = rtnl_dereference(dev_queue->qdisc_sleeping);
- if (!qdisc)
- return;
-
- nolock = qdisc->flags & TCQ_F_NOLOCK;
-
- if (nolock)
- spin_lock_bh(&qdisc->seqlock);
- spin_lock_bh(qdisc_lock(qdisc));
-
- qdisc_reset(qdisc);
-
- spin_unlock_bh(qdisc_lock(qdisc));
- if (nolock) {
- clear_bit(__QDISC_STATE_MISSED, &qdisc->state);
- clear_bit(__QDISC_STATE_DRAINING, &qdisc->state);
- spin_unlock_bh(&qdisc->seqlock);
- }
-}
-
static bool some_qdisc_is_busy(struct net_device *dev)
{
unsigned int i;
diff --git a/net/sched/sch_teql.c b/net/sched/sch_teql.c
index 783300d8b0197..ec4039a201a2c 100644
--- a/net/sched/sch_teql.c
+++ b/net/sched/sch_teql.c
@@ -146,15 +146,12 @@ teql_destroy(struct Qdisc *sch)
master->slaves = NEXT_SLAVE(q);
if (q == master->slaves) {
struct netdev_queue *txq;
- spinlock_t *root_lock;

txq = netdev_get_tx_queue(master->dev, 0);
master->slaves = NULL;

- root_lock = qdisc_root_sleeping_lock(rtnl_dereference(txq->qdisc));
- spin_lock_bh(root_lock);
- qdisc_reset(rtnl_dereference(txq->qdisc));
- spin_unlock_bh(root_lock);
+ dev_reset_queue(master->dev,
+ txq, NULL);
}
}
skb_queue_purge(&dat->q);
--
2.51.0