| Message ID | ed47959b3abc0d03cb98d65581ac2541fa27b16e.1637674769.git.dcaratti@redhat.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net,v2] net/sched: sch_ets: don't peek at classes beyond 'nbands' | expand |
On Tue, Nov 23, 2021 at 5:54 AM Davide Caratti <dcaratti@redhat.com> wrote: > > when the number of DRR classes decreases, the round-robin active list can > contain elements that have already been freed in ets_qdisc_change(). As a > consequence, it's possible to see a NULL dereference crash, caused by the > attempt to call cl->qdisc->ops->peek(cl->qdisc) when cl->qdisc is NULL: Where exactly is it set to NULL? In line 688? 686 for (i = q->nbands; i < oldbands; i++) { 687 qdisc_put(q->classes[i].qdisc); 688 q->classes[i].qdisc = NULL; 689 q->classes[i].quantum = 0; 690 q->classes[i].deficit = 0; 691 gnet_stats_basic_sync_init(&q->classes[i].bstats); 692 memset(&q->classes[i].qstats, 0, sizeof(q->classes[i].qstats)); 693 } If so, your patch is not sufficient as the NULL assignment can happen after the check you add here? Thanks.
hello Cong, thanks for reviewing! On Tue, Nov 23, 2021 at 04:44:46PM -0800, Cong Wang wrote: > On Tue, Nov 23, 2021 at 5:54 AM Davide Caratti <dcaratti@redhat.com> wrote: > > > > when the number of DRR classes decreases, the round-robin active list can > > contain elements that have already been freed in ets_qdisc_change(). As a > > consequence, it's possible to see a NULL dereference crash, caused by the > > attempt to call cl->qdisc->ops->peek(cl->qdisc) when cl->qdisc is NULL: > > Where exactly is it set to NULL? In line 688? yes. At least, yes with the test I'm running to reproduce the crash: # tc qdisc add dev ddd0 handle 10: parent 1: ets bands 8 strict 4 priomap 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 # mausezahn ddd0 -A 10.10.10.1 -B 10.10.10.2 -c 0 -a own -b 00:c1:a0:c1:a0:00 -t udp & # tc qdisc change dev ddd0 handle 10: ets bands 4 strict 2 quanta 2500 2500 priomap 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 > > 686 for (i = q->nbands; i < oldbands; i++) { > 687 qdisc_put(q->classes[i].qdisc); > 688 q->classes[i].qdisc = NULL; > 689 q->classes[i].quantum = 0; > 690 q->classes[i].deficit = 0; > 691 gnet_stats_basic_sync_init(&q->classes[i].bstats); > 692 memset(&q->classes[i].qstats, 0, > sizeof(q->classes[i].qstats)); > 693 } > > If so, your patch is not sufficient as the NULL assignment can happen > after the check you add here? I think you are right, thanks for noticing. Probably we can keep this NULL assignment outside the sch_tree_lock() / sch_tree_unlock(), it's here since the beginning and it's not harmful. We can "heal" the active list in ets_qdisc_change() so that it does not contain elements beyond 'nbands': this is probably better as it doesn't need to add code to the traffic path. I will send a v3 soon.
diff --git a/net/sched/sch_ets.c b/net/sched/sch_ets.c index 0eae9ff5edf6..ecb569ffb3f1 100644 --- a/net/sched/sch_ets.c +++ b/net/sched/sch_ets.c @@ -476,10 +476,15 @@ static struct sk_buff *ets_qdisc_dequeue(struct Qdisc *sch) return ets_qdisc_dequeue_skb(sch, skb); } +drr_dequeue: if (list_empty(&q->active)) goto out; cl = list_first_entry(&q->active, struct ets_class, alist); + if (!cl->qdisc) { + list_del(&cl->alist); + goto drr_dequeue; + } skb = cl->qdisc->ops->peek(cl->qdisc); if (!skb) { qdisc_warn_nonwc(__func__, cl->qdisc);
when the number of DRR classes decreases, the round-robin active list can contain elements that have already been freed in ets_qdisc_change(). As a consequence, it's possible to see a NULL dereference crash, caused by the attempt to call cl->qdisc->ops->peek(cl->qdisc) when cl->qdisc is NULL: BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 1 PID: 910 Comm: mausezahn Not tainted 5.16.0-rc1+ #475 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014 RIP: 0010:ets_qdisc_dequeue+0x129/0x2c0 [sch_ets] Code: c5 01 41 39 ad e4 02 00 00 0f 87 18 ff ff ff 49 8b 85 c0 02 00 00 49 39 c4 0f 84 ba 00 00 00 49 8b ad c0 02 00 00 48 8b 7d 10 <48> 8b 47 18 48 8b 40 38 0f ae e8 ff d0 48 89 c3 48 85 c0 0f 84 9d RSP: 0000:ffffbb36c0b5fdd8 EFLAGS: 00010287 RAX: ffff956678efed30 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000002 RSI: ffffffff9b938dc9 RDI: 0000000000000000 RBP: ffff956678efed30 R08: e2f3207fe360129c R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000001 R12: ffff956678efeac0 R13: ffff956678efe800 R14: ffff956611545000 R15: ffff95667ac8f100 FS: 00007f2aa9120740(0000) GS:ffff95667b800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000018 CR3: 000000011070c000 CR4: 0000000000350ee0 Call Trace: <TASK> qdisc_peek_dequeued+0x29/0x70 [sch_ets] tbf_dequeue+0x22/0x260 [sch_tbf] __qdisc_run+0x7f/0x630 net_tx_action+0x290/0x4c0 __do_softirq+0xee/0x4f8 irq_exit_rcu+0xf4/0x130 sysvec_apic_timer_interrupt+0x52/0xc0 asm_sysvec_apic_timer_interrupt+0x12/0x20 RIP: 0033:0x7f2aa7fc9ad4 Code: b9 ff ff 48 8b 54 24 18 48 83 c4 08 48 89 ee 48 89 df 5b 5d e9 ed fc ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa <53> 48 83 ec 10 48 8b 05 10 64 33 00 48 8b 00 48 85 c0 0f 85 84 00 RSP: 002b:00007ffe5d33fab8 EFLAGS: 00000202 RAX: 0000000000000002 RBX: 0000561f72c31460 RCX: 0000561f72c31720 RDX: 0000000000000002 RSI: 0000561f72c31722 RDI: 0000561f72c31720 RBP: 000000000000002a R08: 00007ffe5d33fa40 R09: 0000000000000014 R10: 0000000000000000 R11: 0000000000000246 R12: 0000561f7187e380 R13: 0000000000000000 R14: 0000000000000000 R15: 0000561f72c31460 </TASK> Modules linked in: sch_ets sch_tbf dummy rfkill iTCO_wdt intel_rapl_msr iTCO_vendor_support intel_rapl_common joydev virtio_balloon lpc_ich i2c_i801 i2c_smbus pcspkr ip_tables xfs libcrc32c crct10dif_pclmul crc32_pclmul crc32c_intel ahci libahci ghash_clmulni_intel serio_raw libata virtio_blk virtio_console virtio_net net_failover failover sunrpc dm_mirror dm_region_hash dm_log dm_mod CR2: 0000000000000018 Ensuring that 'alist' was never zeroed [1] was not sufficient, we need to check also for possible NULL 'qdisc' pointers in the leaf class. [1] https://lore.kernel.org/netdev/60d274838bf09777f0371253416e8af71360bc08.1633609148.git.dcaratti@redhat.com/ v2: when a NULL qdisc is found in the DRR active list, try to dequeue skb from the next list item. Reported-by: Hangbin Liu <liuhangbin@gmail.com> Fixes: dcc68b4d8084 ("net: sch_ets: Add a new Qdisc") Signed-off-by: Davide Caratti <dcaratti@redhat.com> --- net/sched/sch_ets.c | 5 +++++ 1 file changed, 5 insertions(+)