From 458d5615272d3de535748342eb68ca492343048c Mon Sep 17 00:00:00 2001 From: Jamal Hadi Salim Date: Thu, 30 Apr 2026 11:29:55 -0400 Subject: [PATCH 1/3] net/sched: sch_red: Replace direct dequeue call with peek and qdisc_dequeue_peeked When red qdisc has children (eg qfq qdisc) whose peek() callback is qdisc_peek_dequeued(), we could get a kernel panic. When the parent of such qdiscs (eg illustrated in patch #3 as tbf) wants to retrieve an skb from its child (red in this case), it will do the following: 1a. do a peek() - and when sensing there's an skb the child can offer, then - the child in this case(red) calls its child's (qfq) peek. qfq does the right thing and will return the gso_skb queue packet. Note: if there wasnt a gso_skb entry then qfq will store it there. 1b. invoke a dequeue() on the child (red). And herein lies the problem. - red will call the child's dequeue() which will essentially just try to grab something of qfq's queue. [ 78.667668][ T363] KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f] [ 78.667927][ T363] CPU: 1 UID: 0 PID: 363 Comm: ping Not tainted 7.1.0-rc1-00033-g46f74a3f7d57-dirty #790 PREEMPT(full) [ 78.668263][ T363] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 78.668486][ T363] RIP: 0010:qfq_dequeue+0x446/0xc90 [sch_qfq] [ 78.668718][ T363] Code: 54 c0 e8 dd 90 00 f1 48 c7 c7 e0 03 54 c0 48 89 de e8 ce 90 00 f1 48 8d 7b 48 b8 ff ff 37 00 48 89 fa 48 c1 e0 2a 48 c1 ea 03 <80> 3c 02 00 74 05 e8 ef a1 e1 f1 48 8b 7b 48 48 8d 54 24 58 48 8d [ 78.669312][ T363] RSP: 0018:ffff88810de573e0 EFLAGS: 00010216 [ 78.669533][ T363] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 78.669790][ T363] RDX: 0000000000000009 RSI: 0000000000000004 RDI: 0000000000000048 [ 78.670044][ T363] RBP: ffff888110dc4000 R08: ffffffffb1b0885a R09: fffffbfff6ba9078 [ 78.670297][ T363] R10: 0000000000000003 R11: ffff888110e31c80 R12: 0000001880000000 [ 78.670560][ T363] R13: ffff888110dc4150 R14: ffff888110dc42b8 R15: 0000000000000200 [ 78.670814][ T363] FS: 00007f66a8f09c40(0000) GS:ffff888163428000(0000) knlGS:0000000000000000 [ 78.671110][ T363] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 78.671324][ T363] CR2: 000055db4c6a30a8 CR3: 000000010da67000 CR4: 0000000000750ef0 [ 78.671585][ T363] PKRU: 55555554 [ 78.671713][ T363] Call Trace: [ 78.671843][ T363] [ 78.671936][ T363] ? __pfx_qfq_dequeue+0x10/0x10 [sch_qfq] [ 78.672148][ T363] ? __pfx__printk+0x10/0x10 [ 78.672322][ T363] ? srso_alias_return_thunk+0x5/0xfbef5 [ 78.672496][ T363] ? lockdep_hardirqs_on_prepare+0xa8/0x1a0 [ 78.672706][ T363] ? srso_alias_return_thunk+0x5/0xfbef5 [ 78.672875][ T363] ? trace_hardirqs_on+0x19/0x1a0 [ 78.673047][ T363] red_dequeue+0x65/0x270 [sch_red] [ 78.673217][ T363] ? srso_alias_return_thunk+0x5/0xfbef5 [ 78.673385][ T363] tbf_dequeue.cold+0xb0/0x70c [sch_tbf] [ 78.673566][ T363] __qdisc_run+0x169/0x1900 The right thing to do in #1b is to grab the skb off gso_skb queue. This patchset fixes that issue by changing #1b to use qdisc_dequeue_peeked() method instead. Fixes: 77be155cba4e ("pkt_sched: Add peek emulation for non-work-conserving qdiscs.") Reported-by: Manas Reported-by: Rakshit Awasthi Signed-off-by: Jamal Hadi Salim Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260430152957.194015-2-jhs@mojatatu.com Signed-off-by: Jakub Kicinski --- net/sched/sch_red.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/sch_red.c b/net/sched/sch_red.c index 432b8a3000a5..4d0e44a2e7c6 100644 --- a/net/sched/sch_red.c +++ b/net/sched/sch_red.c @@ -162,7 +162,7 @@ static struct sk_buff *red_dequeue(struct Qdisc *sch) struct red_sched_data *q = qdisc_priv(sch); struct Qdisc *child = q->qdisc; - skb = child->dequeue(child); + skb = qdisc_dequeue_peeked(child); if (skb) { qdisc_bstats_update(sch, skb); qdisc_qstats_backlog_dec(sch, skb); From 1b9bc71153b01dbde8045b9edede4240f4f5520e Mon Sep 17 00:00:00 2001 From: Victor Nogueria Date: Thu, 30 Apr 2026 11:29:56 -0400 Subject: [PATCH 2/3] net/sched: sch_sfb: Replace direct dequeue call with peek and qdisc_dequeue_peeked When sfb has children (eg qfq qdisc) whose peek() callback is qdisc_peek_dequeued(), we could get a kernel panic. When the parent of such qdiscs (eg illustrated in patch #3 as tbf) wants to retrieve an skb from its child (sfb in this case), it will do the following: 1a. do a peek() - and when sensing there's an skb the child can offer, then - the child in this case(sfb) calls its child's (qfq) peek. qfq does the right thing and will return the gso_skb queue packet. Note: if there wasnt a gso_skb entry then qfq will store it there. 1b. invoke a dequeue() on the child (sfb). And herein lies the problem. - sfb will call the child's dequeue() which will essentially just try to grab something of qfq's queue. [ 127.594489][ T453] KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f] [ 127.594741][ T453] CPU: 2 UID: 0 PID: 453 Comm: ping Not tainted 7.1.0-rc1-00035-gac961974495b-dirty #793 PREEMPT(full) [ 127.595059][ T453] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 127.595254][ T453] RIP: 0010:qfq_dequeue+0x35c/0x1650 [sch_qfq] [ 127.595461][ T453] Code: 00 fc ff df 80 3c 02 00 0f 85 17 0e 00 00 4c 8d 73 48 48 89 9d b8 02 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <80> 3c 02 00 0f 85 76 0c 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b [ 127.596081][ T453] RSP: 0018:ffff88810e5af440 EFLAGS: 00010216 [ 127.596337][ T453] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: dffffc0000000000 [ 127.596623][ T453] RDX: 0000000000000009 RSI: 0000001880000000 RDI: ffff888104fd82b0 [ 127.596917][ T453] RBP: ffff888104fd8000 R08: ffff888104fd8280 R09: 1ffff110211893a3 [ 127.597165][ T453] R10: 1ffff110211893a6 R11: 1ffff110211893a7 R12: 0000001880000000 [ 127.597404][ T453] R13: ffff888104fd82b8 R14: 0000000000000048 R15: 0000000040000000 [ 127.597644][ T453] FS: 00007fc380cbfc40(0000) GS:ffff88816f2a8000(0000) knlGS:0000000000000000 [ 127.597956][ T453] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 127.598160][ T453] CR2: 00005610aa9890a8 CR3: 000000010369e000 CR4: 0000000000750ef0 [ 127.598390][ T453] PKRU: 55555554 [ 127.598509][ T453] Call Trace: [ 127.598629][ T453] [ 127.598718][ T453] ? mark_held_locks+0x40/0x70 [ 127.598890][ T453] ? srso_alias_return_thunk+0x5/0xfbef5 [ 127.599053][ T453] sfb_dequeue+0x88/0x4d0 [ 127.599174][ T453] ? ktime_get+0x137/0x230 [ 127.599328][ T453] ? srso_alias_return_thunk+0x5/0xfbef5 [ 127.599480][ T453] ? qdisc_peek_dequeued+0x7b/0x350 [sch_qfq] [ 127.599670][ T453] ? srso_alias_return_thunk+0x5/0xfbef5 [ 127.599831][ T453] tbf_dequeue+0x6b1/0x1098 [sch_tbf] [ 127.599988][ T453] __qdisc_run+0x169/0x1900 The right thing to do in #1b is to grab the skb off gso_skb queue. This patchset fixes that issue by changing #1b to use qdisc_dequeue_peeked() method instead. Fixes: e13e02a3c68d ("net_sched: SFB flow scheduler") Signed-off-by: Victor Nogueria Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260430152957.194015-3-jhs@mojatatu.com Signed-off-by: Jakub Kicinski --- net/sched/sch_sfb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/sch_sfb.c b/net/sched/sch_sfb.c index bd5ef561030f..d3ee8e5479b3 100644 --- a/net/sched/sch_sfb.c +++ b/net/sched/sch_sfb.c @@ -441,7 +441,7 @@ static struct sk_buff *sfb_dequeue(struct Qdisc *sch) struct Qdisc *child = q->qdisc; struct sk_buff *skb; - skb = child->dequeue(q->qdisc); + skb = qdisc_dequeue_peeked(child); if (skb) { qdisc_bstats_update(sch, skb); From 3a3a30c14d7f04206916824a79878cfefac6c8e2 Mon Sep 17 00:00:00 2001 From: Victor Nogueira Date: Thu, 30 Apr 2026 11:29:57 -0400 Subject: [PATCH 3/3] selftests/tc-testing: Add tests that force red and sfb to dequeue from child's gso_skb Create 4 test cases: - Force red to dequeue from its child's gso_skb with qfq leaf - Force sfb to dequeue from its child's gso_skb with qfq leaf - Force red to dequeue from its child's gso_skb with dualpi2 leaf - Force sfb to dequeue from its child's gso_skb with dualpi2 leaf All of them have tbf followed by red (or sfb) followed by qfq (or dualpi2). Since tbf calls its child's peek followed by qdisc_dequeue_peeked, it will force red/sfb to call their child's peek. In this case, since the child (qfq/dualpi2) has qdisc_peek_dequeued as its peek callback, the packet will be stored in its gso_skb queue. During the subsequent call to qdisc_dequeue_peeked, red/sfb will have to dequeue from the child's gso_skb to retrieve the packet. Not doing so will cause a NULL ptr deref which was happening before a recent fix. Acked-by: Jamal Hadi Salim Signed-off-by: Victor Nogueira Link: https://patch.msgid.link/20260430152957.194015-4-jhs@mojatatu.com Signed-off-by: Jakub Kicinski --- .../tc-testing/tc-tests/infra/qdiscs.json | 148 ++++++++++++++++++ 1 file changed, 148 insertions(+) diff --git a/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json b/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json index eefadd0546d3..b1f856cf62c1 100644 --- a/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json +++ b/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json @@ -1136,5 +1136,153 @@ "teardown": [ "$TC qdisc del dev $DUMMY handle 1: root" ] + }, + { + "id": "7a5f", + "name": "Force red to dequeue from its child's gso_skb with qfq leaf", + "category": [ + "qdisc", + "tbf", + "red", + "qfq" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + "$IP link set dev $DUMMY up || true", + "$IP addr add 10.10.11.10/24 dev $DUMMY || true", + "$TC qdisc add dev $DUMMY root handle 1: tbf rate 88bit burst 1661b peakrate 2257333 minburst 1024 limit 7b", + "$TC qdisc add dev $DUMMY parent 1: handle 2: red limit 757 min 16 max 24 avpkt 16", + "$TC qdisc add dev $DUMMY parent 2: handle 3: qfq", + "$TC class add dev $DUMMY classid 3:1 parent 3: qfq maxpkt 512 weight 1", + "$TC filter add dev $DUMMY parent 3: protocol ip prio 1 matchall classid 3:1 action ok" + ], + "cmdUnderTest": "ping -c 1 10.10.10.1 -W0.01 -I$DUMMY || true", + "expExitCode": "0", + "verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:", + "matchJSON": [ + { + "kind": "red", + "handle": "2:", + "bytes": 98, + "packets": 1, + "backlog": 0, + "qlen": 0 + } + ], + "teardown": [ + "$TC qdisc del dev $DUMMY handle 1: root" + ] + }, + { + "id": "cdae", + "name": "Force sfb to dequeue from its child's gso_skb with qfq leaf", + "category": [ + "qdisc", + "tbf", + "sfb", + "qfq" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + "$IP link set dev $DUMMY up || true", + "$IP addr add 10.10.11.10/24 dev $DUMMY || true", + "$TC qdisc add dev $DUMMY root handle 1: tbf rate 88bit burst 1661b peakrate 2257333 minburst 1024 limit 7b", + "$TC qdisc add dev $DUMMY parent 1: handle 2: sfb", + "$TC qdisc add dev $DUMMY parent 2: handle 3: qfq", + "$TC class add dev $DUMMY classid 3:1 parent 3: qfq maxpkt 512 weight 1", + "$TC filter add dev $DUMMY parent 3: protocol ip prio 1 matchall classid 3:1 action ok" + ], + "cmdUnderTest": "ping -c 1 10.10.10.1 -W0.01 -I$DUMMY || true", + "expExitCode": "0", + "verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:", + "matchJSON": [ + { + "kind": "sfb", + "handle": "2:", + "bytes": 98, + "packets": 1, + "backlog": 0, + "qlen": 0 + } + ], + "teardown": [ + "$TC qdisc del dev $DUMMY handle 1: root" + ] + }, + { + "id": "291d", + "name": "Force red to dequeue from its child's gso_skb with dualpi2 leaf", + "category": [ + "qdisc", + "tbf", + "red", + "dualpi2" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + "$IP link set dev $DUMMY up || true", + "$IP addr add 10.10.11.10/24 dev $DUMMY || true", + "$TC qdisc add dev $DUMMY root handle 1: tbf rate 88bit burst 1661b peakrate 2257333 minburst 1024 limit 7b", + "$TC qdisc add dev $DUMMY parent 1: handle 2: red limit 757 min 16 max 24 avpkt 16", + "$TC qdisc add dev $DUMMY parent 2: handle 3: dualpi2" + ], + "cmdUnderTest": "ping -c 1 10.10.10.1 -W0.01 -I$DUMMY || true", + "expExitCode": "0", + "verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:", + "matchJSON": [ + { + "kind": "red", + "handle": "2:", + "bytes": 98, + "packets": 1, + "backlog": 0, + "qlen": 0 + } + ], + "teardown": [ + "$TC qdisc del dev $DUMMY handle 1: root" + ] + }, + { + "id": "9c6d", + "name": "Force sfb to dequeue from its child's gso_skb with dualpi2 leaf", + "category": [ + "qdisc", + "tbf", + "sfb", + "dualpi2" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + "$IP link set dev $DUMMY up || true", + "$IP addr add 10.10.11.10/24 dev $DUMMY || true", + "$TC qdisc add dev $DUMMY root handle 1: tbf rate 88bit burst 1661b peakrate 2257333 minburst 1024 limit 7b", + "$TC qdisc add dev $DUMMY parent 1: handle 2: sfb", + "$TC qdisc add dev $DUMMY parent 2: handle 3: dualpi2" + ], + "cmdUnderTest": "ping -c 1 10.10.10.1 -W0.01 -I$DUMMY || true", + "expExitCode": "0", + "verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:", + "matchJSON": [ + { + "kind": "sfb", + "handle": "2:", + "bytes": 98, + "packets": 1, + "backlog": 0, + "qlen": 0 + } + ], + "teardown": [ + "$TC qdisc del dev $DUMMY handle 1: root" + ] } ]