Subject: Re: [PATCH v3 net] net/sched: taprio: Limit TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME to INT_MAX.

From: Vinicius Costa Gomes <[email-masked]>
Date: Fri, 28 Jul 2023 17:17:34 -0700

Kuniyuki Iwashima <[email-masked]> writes:

> syzkaller found zero division error [0] in div_s64_rem() called from
> get_cycle_time_elapsed(), where sched->cycle_time is the divisor.
>
> We have tests in parse_taprio_schedule() so that cycle_time will never
> be 0, and actually cycle_time is not 0 in get_cycle_time_elapsed().
>
> The problem is that the types of divisor are different; cycle_time is
> s64, but the argument of div_s64_rem() is s32.
>
> syzkaller fed this input and 0x100000000 is cast to s32 to be 0.
>
>   @TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME={0xc, 0x8, 0x100000000}
>
> We use s64 for cycle_time to cast it to ktime_t, so let's keep it and
> set max for cycle_time.
>
> While at it, we prevent overflow in setup_txtime() and add another
> test in parse_taprio_schedule() to check if cycle_time overflows.
>
> Also, we add a new tdc test case for this issue.
>
> [0]:
> divide error: 0000 [#1] PREEMPT SMP KASAN NOPTI
> CPU: 1 PID: 103 Comm: kworker/1:3 Not tainted 6.5.0-rc1-00330-g60cc1f7d0605 #3
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> Workqueue: ipv6_addrconf addrconf_dad_work
> RIP: 0010:div_s64_rem include/linux/math64.h:42 [inline]
> RIP: 0010:get_cycle_time_elapsed net/sched/sch_taprio.c:223 [inline]
> RIP: 0010:find_entry_to_transmit+0x252/0x7e0 net/sched/sch_taprio.c:344
> Code: 3c 02 00 0f 85 5e 05 00 00 48 8b 4c 24 08 4d 8b bd 40 01 00 00 48 8b 7c 24 48 48 89 c8 4c 29 f8 48 63 f7 48 99 48 89 74 24 70 <48> f7 fe 48 29 d1 48 8d 04 0f 49 89 cc 48 89 44 24 20 49 8d 85 10
> RSP: 0018:ffffc90000acf260 EFLAGS: 00010206
> RAX: 177450e0347560cf RBX: 0000000000000000 RCX: 177450e0347560cf
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000100000000
> RBP: 0000000000000056 R08: 0000000000000000 R09: ffffed10020a0934
> R10: ffff8880105049a7 R11: ffff88806cf3a520 R12: ffff888010504800
> R13: ffff88800c00d800 R14: ffff8880105049a0 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff88806cf00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f0edf84f0e8 CR3: 000000000d73c002 CR4: 0000000000770ee0
> PKRU: 55555554
> Call Trace:
>  <TASK>
>  get_packet_txtime net/sched/sch_taprio.c:508 [inline]
>  taprio_enqueue_one+0x900/0xff0 net/sched/sch_taprio.c:577
>  taprio_enqueue+0x378/0xae0 net/sched/sch_taprio.c:658
>  dev_qdisc_enqueue+0x46/0x170 net/core/dev.c:3732
>  __dev_xmit_skb net/core/dev.c:3821 [inline]
>  __dev_queue_xmit+0x1b2f/0x3000 net/core/dev.c:4169
>  dev_queue_xmit include/linux/netdevice.h:3088 [inline]
>  neigh_resolve_output net/core/neighbour.c:1552 [inline]
>  neigh_resolve_output+0x4a7/0x780 net/core/neighbour.c:1532
>  neigh_output include/net/neighbour.h:544 [inline]
>  ip6_finish_output2+0x924/0x17d0 net/ipv6/ip6_output.c:135
>  __ip6_finish_output+0x620/0xaa0 net/ipv6/ip6_output.c:196
>  ip6_finish_output net/ipv6/ip6_output.c:207 [inline]
>  NF_HOOK_COND include/linux/netfilter.h:292 [inline]
>  ip6_output+0x206/0x410 net/ipv6/ip6_output.c:228
>  dst_output include/net/dst.h:458 [inline]
>  NF_HOOK.constprop.0+0xea/0x260 include/linux/netfilter.h:303
>  ndisc_send_skb+0x872/0xe80 net/ipv6/ndisc.c:508
>  ndisc_send_ns+0xb5/0x130 net/ipv6/ndisc.c:666
>  addrconf_dad_work+0xc14/0x13f0 net/ipv6/addrconf.c:4175
>  process_one_work+0x92c/0x13a0 kernel/workqueue.c:2597
>  worker_thread+0x60f/0x1240 kernel/workqueue.c:2748
>  kthread+0x2fe/0x3f0 kernel/kthread.c:389
>  ret_from_fork+0x2c/0x50 arch/x86/entry/entry_64.S:308
>  </TASK>
> Modules linked in:
>
> Fixes: 4cfd5779bd6e ("taprio: Add support for txtime-assist mode")
> Reported-by: syzkaller <[email-masked]>
> Signed-off-by: Kuniyuki Iwashima <[email-masked]>
> Co-developed-by: Eric Dumazet <[email-masked]>
> Co-developed-by: Pedro Tammela <[email-masked]>

Acked-by: Vinicius Costa Gomes <[email-masked]>

Cheers,
-- 
Vinicius