Re: [PATCH v1 net] net/sched: taprio: Limit TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME to INT_MAX.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Eric Dumazet <edumazet@google.com>
Date: Wed, 26 Jul 2023 15:54:12 +0200
> On Wed, Jul 26, 2023 at 3:15 AM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
> >
> > syzkaller found a 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 min/max for cycle_time.
> >
> > [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 <syzkaller@googlegroups.com>
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > ---
> >  net/sched/sch_taprio.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> > index 717ae51d94a0..72808acb5435 100644
> > --- a/net/sched/sch_taprio.c
> > +++ b/net/sched/sch_taprio.c
> > @@ -1015,6 +1015,11 @@ static const struct nla_policy taprio_tc_policy[TCA_TAPRIO_TC_ENTRY_MAX + 1] = {
> >                                                               TC_FP_PREEMPTIBLE),
> >  };
> >
> > +static struct netlink_range_validation_signed taprio_cycle_time_range = {
> > +       .min = 1,
> > +       .max = INT_MAX,
> > +};
> > +
> >  static const struct nla_policy taprio_policy[TCA_TAPRIO_ATTR_MAX + 1] = {
> >         [TCA_TAPRIO_ATTR_PRIOMAP]              = {
> >                 .len = sizeof(struct tc_mqprio_qopt)
> > @@ -1023,7 +1028,8 @@ static const struct nla_policy taprio_policy[TCA_TAPRIO_ATTR_MAX + 1] = {
> >         [TCA_TAPRIO_ATTR_SCHED_BASE_TIME]            = { .type = NLA_S64 },
> >         [TCA_TAPRIO_ATTR_SCHED_SINGLE_ENTRY]         = { .type = NLA_NESTED },
> >         [TCA_TAPRIO_ATTR_SCHED_CLOCKID]              = { .type = NLA_S32 },
> > -       [TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME]           = { .type = NLA_S64 },
> > +       [TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME]           =
> > +               NLA_POLICY_FULL_RANGE_SIGNED(NLA_S64, &taprio_cycle_time_range),
> >         [TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION] = { .type = NLA_S64 },
> >         [TCA_TAPRIO_ATTR_FLAGS]                      = { .type = NLA_U32 },
> >         [TCA_TAPRIO_ATTR_TXTIME_DELAY]               = { .type = NLA_U32 },
> > --
> > 2.30.2
> >
> 
> Not sure this is enough (syzbot could very well find other ways to
> trigger bugs caused by overflows)
> 
> What about setup_txtime() ? It seems possible to have overflows there...
> 
> What about adding to your patch the following ?

Ah good catch!
I'll post v2 with Co-developed-by :)

Thanks!


> 
> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> index 717ae51d94a0ae4f45317e8ba86f51ab4ac41aa6..a4bdc5d8bd6fc546bc835c953db81cdaf7285a40
> 100644
> --- a/net/sched/sch_taprio.c
> +++ b/net/sched/sch_taprio.c
> @@ -1158,7 +1158,10 @@ static int parse_taprio_schedule(struct
> taprio_sched *q, struct nlattr **tb,
>                         NL_SET_ERR_MSG(extack, "'cycle_time' can never be 0");
>                         return -EINVAL;
>                 }
> -
> +               if (cycle > INT_MAX) {
> +                       NL_SET_ERR_MSG(extack, "'cycle_time' is too big");
> +                       return -EINVAL;
> +               }
>                 new->cycle_time = cycle;
>         }
> 
> @@ -1347,7 +1350,7 @@ static void setup_txtime(struct taprio_sched *q,
>                          struct sched_gate_list *sched, ktime_t base)
>  {
>         struct sched_entry *entry;
> -       u32 interval = 0;
> +       u64 interval = 0;
> 
>         list_for_each_entry(entry, &sched->entries, list) {
>                 entry->next_txtime = ktime_add_ns(base, interval);
>