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* net/sched: GPF in qdisc_hash_add
@ 2017-03-23 16:06 Dmitry Vyukov
  2017-03-23 19:00 ` Cong Wang
  0 siblings, 1 reply; 5+ messages in thread
From: Dmitry Vyukov @ 2017-03-23 16:06 UTC (permalink / raw)
  To: Jamal Hadi Salim, David Miller, netdev, LKML, Cong Wang, Eric Dumazet
  Cc: syzkaller

Hello,

I've hit the following GPF while running syzkaller on commit
093b995e3b55a0ae0670226ddfcb05bfbf0099ae.  Note the preceding injected
kmalloc failure, most likely it's the root cause.

FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 0
CPU: 2 PID: 12732 Comm: syz-executor6 Not tainted 4.11.0-rc3+ #365
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x1b8/0x28d lib/dump_stack.c:52
 fail_dump lib/fault-inject.c:52 [inline]
 should_fail+0x804/0x8c0 lib/fault-inject.c:154
 should_failslab+0xec/0x120 mm/failslab.c:31
 slab_pre_alloc_hook mm/slab.h:434 [inline]
 slab_alloc_node mm/slab.c:3315 [inline]
 kmem_cache_alloc_node_trace+0x200/0x720 mm/slab.c:3679
 __do_kmalloc_node mm/slab.c:3699 [inline]
 __kmalloc_node+0x33/0x70 mm/slab.c:3707
 kmalloc_node include/linux/slab.h:532 [inline]
 kzalloc_node include/linux/slab.h:674 [inline]
 qdisc_alloc+0xf4/0x670 net/sched/sch_generic.c:604
 qdisc_create_dflt+0x59/0x160 net/sched/sch_generic.c:652
 attach_one_default_qdisc net/sched/sch_generic.c:767 [inline]
 netdev_for_each_tx_queue include/linux/netdevice.h:1948 [inline]
 attach_default_qdiscs net/sched/sch_generic.c:786 [inline]
 dev_activate+0x58d/0x920 net/sched/sch_generic.c:829
 __dev_open+0x25b/0x360 net/core/dev.c:1348
 __dev_change_flags+0x159/0x3d0 net/core/dev.c:6460
 dev_change_flags+0x88/0x140 net/core/dev.c:6525
 dev_ifsioc+0x51f/0x9b0 net/core/dev_ioctl.c:254
 dev_ioctl+0x1fe/0x1030 net/core/dev_ioctl.c:532
 sock_do_ioctl+0x94/0xb0 net/socket.c:902
 sock_ioctl+0x2c2/0x440 net/socket.c:993
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x445b79
RSP: 002b:00007f68665cf858 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 0000000000445b79
RDX: 0000000020000000 RSI: 0000000000008914 RDI: 0000000000000019
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00000000004a7e31
R13: 0000000000000000 R14: 00007f68665cf618 R15: 00007f68665cf788
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 2 PID: 12732 Comm: syz-executor6 Not tainted 4.11.0-rc3+ #365
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff880062b7a2c0 task.stack: ffff880033480000
RIP: 0010:qdisc_hash_add.part.19+0xb6/0x3c0 net/sched/sch_api.c:280
RSP: 0018:ffff880033487820 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffffff85357e00 RCX: ffffc90002b24000
RDX: 000000000000007a RSI: ffffffff835a523a RDI: 00000000000003d0
RBP: ffff8800334878b8 R08: fffffbfff0a6afeb R09: fffffbfff0a6afeb
R10: 0000000000000001 R11: fffffbfff0a6afea R12: ffffffff85357e48
R13: 1ffff10006690f06 R14: ffff880033487890 R15: 0000000000000000
FS:  00007f68665d0700(0000) GS:ffff88006e200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004c2d44 CR3: 000000003c6f8000 CR4: 00000000000026e0
Call Trace:
 qdisc_hash_add+0x76/0x90 net/sched/sch_api.c:279
 attach_default_qdiscs net/sched/sch_generic.c:798 [inline]
 dev_activate+0x6ca/0x920 net/sched/sch_generic.c:829
 __dev_open+0x25b/0x360 net/core/dev.c:1348
 __dev_change_flags+0x159/0x3d0 net/core/dev.c:6460
 dev_change_flags+0x88/0x140 net/core/dev.c:6525
 dev_ifsioc+0x51f/0x9b0 net/core/dev_ioctl.c:254
 dev_ioctl+0x1fe/0x1030 net/core/dev_ioctl.c:532
 sock_do_ioctl+0x94/0xb0 net/socket.c:902
 sock_ioctl+0x2c2/0x440 net/socket.c:993
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x445b79
RSP: 002b:00007f68665cf858 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 0000000000445b79
RDX: 0000000020000000 RSI: 0000000000008914 RDI: 0000000000000019
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00000000004a7e31
R13: 0000000000000000 R14: 00007f68665cf618 R15: 00007f68665cf788
Code: 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 5a 02 00 00 4d 8b 3f 48 b8
00 00 00 00 00 fc ff df 49 8d bf d0 03 00 00 48 89 fa 48 c1 ea 03 <80>
3c 02 00 0f 85 c2 02 00 00 49 81 bf d0 03 00 00 00 7e 35 85
RIP: qdisc_hash_add.part.19+0xb6/0x3c0 net/sched/sch_api.c:280 RSP:
ffff880033487820
---[ end trace 1529d12967754f9c ]---

^ permalink raw reply	[flat|nested] 5+ messages in thread
* Re: net/sched: GPF in qdisc_hash_add
  2017-03-23 16:06 net/sched: GPF in qdisc_hash_add Dmitry Vyukov
@ 2017-03-23 19:00 ` Cong Wang
  2017-03-23 19:06   ` Dmitry Vyukov
  0 siblings, 1 reply; 5+ messages in thread
From: Cong Wang @ 2017-03-23 19:00 UTC (permalink / raw)
  To: Dmitry Vyukov
  Cc: Jamal Hadi Salim, David Miller, netdev, LKML, Eric Dumazet, syzkaller

On Thu, Mar 23, 2017 at 9:06 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 2 PID: 12732 Comm: syz-executor6 Not tainted 4.11.0-rc3+ #365
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff880062b7a2c0 task.stack: ffff880033480000
> RIP: 0010:qdisc_hash_add.part.19+0xb6/0x3c0 net/sched/sch_api.c:280
> RSP: 0018:ffff880033487820 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: ffffffff85357e00 RCX: ffffc90002b24000
> RDX: 000000000000007a RSI: ffffffff835a523a RDI: 00000000000003d0
> RBP: ffff8800334878b8 R08: fffffbfff0a6afeb R09: fffffbfff0a6afeb
> R10: 0000000000000001 R11: fffffbfff0a6afea R12: ffffffff85357e48
> R13: 1ffff10006690f06 R14: ffff880033487890 R15: 0000000000000000
> FS:  00007f68665d0700(0000) GS:ffff88006e200000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000004c2d44 CR3: 000000003c6f8000 CR4: 00000000000026e0
> Call Trace:
>  qdisc_hash_add+0x76/0x90 net/sched/sch_api.c:279
>  attach_default_qdiscs net/sched/sch_generic.c:798 [inline]
>  dev_activate+0x6ca/0x920 net/sched/sch_generic.c:829
>  __dev_open+0x25b/0x360 net/core/dev.c:1348
>  __dev_change_flags+0x159/0x3d0 net/core/dev.c:6460
>  dev_change_flags+0x88/0x140 net/core/dev.c:6525
>  dev_ifsioc+0x51f/0x9b0 net/core/dev_ioctl.c:254
>  dev_ioctl+0x1fe/0x1030 net/core/dev_ioctl.c:532
>  sock_do_ioctl+0x94/0xb0 net/socket.c:902
>  sock_ioctl+0x2c2/0x440 net/socket.c:993
>  vfs_ioctl fs/ioctl.c:45 [inline]
>  do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
>  SYSC_ioctl fs/ioctl.c:700 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>  entry_SYSCALL_64_fastpath+0x1f/0xc2

The interesting part is why the NULL dereference is in
qdisc_hash_add(), since we have a check before calling
it:

#ifdef CONFIG_NET_SCHED
        if (dev->qdisc)
                qdisc_hash_add(dev->qdisc);
#endif


When attach_one_default_qdisc() fails, we should trigger
the NULL pointer dereference bug at:

    atomic_inc(&dev->qdisc->refcnt);

^ permalink raw reply	[flat|nested] 5+ messages in thread
* Re: net/sched: GPF in qdisc_hash_add
  2017-03-23 19:00 ` Cong Wang
@ 2017-03-23 19:06   ` Dmitry Vyukov
  2017-03-23 19:10     ` Eric Dumazet
  0 siblings, 1 reply; 5+ messages in thread
From: Dmitry Vyukov @ 2017-03-23 19:06 UTC (permalink / raw)
  To: Cong Wang
  Cc: Jamal Hadi Salim, David Miller, netdev, LKML, Eric Dumazet, syzkaller

On Thu, Mar 23, 2017 at 8:00 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> On Thu, Mar 23, 2017 at 9:06 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
>> kasan: CONFIG_KASAN_INLINE enabled
>> kasan: GPF could be caused by NULL-ptr deref or user memory access
>> general protection fault: 0000 [#1] SMP KASAN
>> Dumping ftrace buffer:
>>    (ftrace buffer empty)
>> Modules linked in:
>> CPU: 2 PID: 12732 Comm: syz-executor6 Not tainted 4.11.0-rc3+ #365
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> task: ffff880062b7a2c0 task.stack: ffff880033480000
>> RIP: 0010:qdisc_hash_add.part.19+0xb6/0x3c0 net/sched/sch_api.c:280
>> RSP: 0018:ffff880033487820 EFLAGS: 00010202
>> RAX: dffffc0000000000 RBX: ffffffff85357e00 RCX: ffffc90002b24000
>> RDX: 000000000000007a RSI: ffffffff835a523a RDI: 00000000000003d0
>> RBP: ffff8800334878b8 R08: fffffbfff0a6afeb R09: fffffbfff0a6afeb
>> R10: 0000000000000001 R11: fffffbfff0a6afea R12: ffffffff85357e48
>> R13: 1ffff10006690f06 R14: ffff880033487890 R15: 0000000000000000
>> FS:  00007f68665d0700(0000) GS:ffff88006e200000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00000000004c2d44 CR3: 000000003c6f8000 CR4: 00000000000026e0
>> Call Trace:
>>  qdisc_hash_add+0x76/0x90 net/sched/sch_api.c:279
>>  attach_default_qdiscs net/sched/sch_generic.c:798 [inline]
>>  dev_activate+0x6ca/0x920 net/sched/sch_generic.c:829
>>  __dev_open+0x25b/0x360 net/core/dev.c:1348
>>  __dev_change_flags+0x159/0x3d0 net/core/dev.c:6460
>>  dev_change_flags+0x88/0x140 net/core/dev.c:6525
>>  dev_ifsioc+0x51f/0x9b0 net/core/dev_ioctl.c:254
>>  dev_ioctl+0x1fe/0x1030 net/core/dev_ioctl.c:532
>>  sock_do_ioctl+0x94/0xb0 net/socket.c:902
>>  sock_ioctl+0x2c2/0x440 net/socket.c:993
>>  vfs_ioctl fs/ioctl.c:45 [inline]
>>  do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
>>  SYSC_ioctl fs/ioctl.c:700 [inline]
>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>>  entry_SYSCALL_64_fastpath+0x1f/0xc2
>
> The interesting part is why the NULL dereference is in
> qdisc_hash_add(), since we have a check before calling
> it:
>
> #ifdef CONFIG_NET_SCHED
>         if (dev->qdisc)
>                 qdisc_hash_add(dev->qdisc);
> #endif
>
>
> When attach_one_default_qdisc() fails, we should trigger
> the NULL pointer dereference bug at:
>
>     atomic_inc(&dev->qdisc->refcnt);

I think qdisc is not NULL, it's something _in_ qdisc that is NULL. The
crash happens here:

                struct Qdisc *root = qdisc_dev(q)->qdisc;

so it's probably device.

^ permalink raw reply	[flat|nested] 5+ messages in thread
* Re: net/sched: GPF in qdisc_hash_add
  2017-03-23 19:06   ` Dmitry Vyukov
@ 2017-03-23 19:10     ` Eric Dumazet
  2017-03-24 17:28       ` Cong Wang
  0 siblings, 1 reply; 5+ messages in thread
From: Eric Dumazet @ 2017-03-23 19:10 UTC (permalink / raw)
  To: Dmitry Vyukov
  Cc: Cong Wang, Jamal Hadi Salim, David Miller, netdev, LKML, syzkaller

On Thu, Mar 23, 2017 at 12:06 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Thu, Mar 23, 2017 at 8:00 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> > On Thu, Mar 23, 2017 at 9:06 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> >> kasan: CONFIG_KASAN_INLINE enabled
> >> kasan: GPF could be caused by NULL-ptr deref or user memory access
> >> general protection fault: 0000 [#1] SMP KASAN
> >> Dumping ftrace buffer:
> >>    (ftrace buffer empty)
> >> Modules linked in:
> >> CPU: 2 PID: 12732 Comm: syz-executor6 Not tainted 4.11.0-rc3+ #365
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> >> task: ffff880062b7a2c0 task.stack: ffff880033480000
> >> RIP: 0010:qdisc_hash_add.part.19+0xb6/0x3c0 net/sched/sch_api.c:280
> >> RSP: 0018:ffff880033487820 EFLAGS: 00010202
> >> RAX: dffffc0000000000 RBX: ffffffff85357e00 RCX: ffffc90002b24000
> >> RDX: 000000000000007a RSI: ffffffff835a523a RDI: 00000000000003d0
> >> RBP: ffff8800334878b8 R08: fffffbfff0a6afeb R09: fffffbfff0a6afeb
> >> R10: 0000000000000001 R11: fffffbfff0a6afea R12: ffffffff85357e48
> >> R13: 1ffff10006690f06 R14: ffff880033487890 R15: 0000000000000000
> >> FS:  00007f68665d0700(0000) GS:ffff88006e200000(0000) knlGS:0000000000000000
> >> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> CR2: 00000000004c2d44 CR3: 000000003c6f8000 CR4: 00000000000026e0
> >> Call Trace:
> >>  qdisc_hash_add+0x76/0x90 net/sched/sch_api.c:279
> >>  attach_default_qdiscs net/sched/sch_generic.c:798 [inline]
> >>  dev_activate+0x6ca/0x920 net/sched/sch_generic.c:829
> >>  __dev_open+0x25b/0x360 net/core/dev.c:1348
> >>  __dev_change_flags+0x159/0x3d0 net/core/dev.c:6460
> >>  dev_change_flags+0x88/0x140 net/core/dev.c:6525
> >>  dev_ifsioc+0x51f/0x9b0 net/core/dev_ioctl.c:254
> >>  dev_ioctl+0x1fe/0x1030 net/core/dev_ioctl.c:532
> >>  sock_do_ioctl+0x94/0xb0 net/socket.c:902
> >>  sock_ioctl+0x2c2/0x440 net/socket.c:993
> >>  vfs_ioctl fs/ioctl.c:45 [inline]
> >>  do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
> >>  SYSC_ioctl fs/ioctl.c:700 [inline]
> >>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
> >>  entry_SYSCALL_64_fastpath+0x1f/0xc2
> >
> > The interesting part is why the NULL dereference is in
> > qdisc_hash_add(), since we have a check before calling
> > it:
> >
> > #ifdef CONFIG_NET_SCHED
> >         if (dev->qdisc)
> >                 qdisc_hash_add(dev->qdisc);
> > #endif
> >
> >
> > When attach_one_default_qdisc() fails, we should trigger
> > the NULL pointer dereference bug at:
> >
> >     atomic_inc(&dev->qdisc->refcnt);
>
> I think qdisc is not NULL, it's something _in_ qdisc that is NULL. The
> crash happens here:
>
>                 struct Qdisc *root = qdisc_dev(q)->qdisc;
>
> so it's probably device.



Looks like this bug came with commit 59cc1f61f09c
("net: sched: convert qdisc linked list to hashtable")

I would simply guard qdisc_hash_add()

(Against &noop_qdisc)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index bcf49cd2278670197f2a7e9d4e9a62ae8d117468..2bb34b51cffdb05434a488b9f45c344d57868253
100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -276,6 +276,8 @@ static struct Qdisc *qdisc_match_from_root(struct
Qdisc *root, u32 handle)

 void qdisc_hash_add(struct Qdisc *q)
 {
+ if (q == &noop_qdisc)
+ return;
  if ((q->parent != TC_H_ROOT) && !(q->flags & TCQ_F_INGRESS)) {
  struct Qdisc *root = qdisc_dev(q)->qdisc;

^ permalink raw reply	[flat|nested] 5+ messages in thread
* Re: net/sched: GPF in qdisc_hash_add
  2017-03-23 19:10     ` Eric Dumazet
@ 2017-03-24 17:28       ` Cong Wang
  0 siblings, 0 replies; 5+ messages in thread
From: Cong Wang @ 2017-03-24 17:28 UTC (permalink / raw)
  To: Eric Dumazet
  Cc: Dmitry Vyukov, Jamal Hadi Salim, David Miller, netdev, LKML, syzkaller

On Thu, Mar 23, 2017 at 12:10 PM, Eric Dumazet <edumazet@google.com> wrote:
> On Thu, Mar 23, 2017 at 12:06 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>>
>> On Thu, Mar 23, 2017 at 8:00 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>> > On Thu, Mar 23, 2017 at 9:06 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
>> >> kasan: CONFIG_KASAN_INLINE enabled
>> >> kasan: GPF could be caused by NULL-ptr deref or user memory access
>> >> general protection fault: 0000 [#1] SMP KASAN
>> >> Dumping ftrace buffer:
>> >>    (ftrace buffer empty)
>> >> Modules linked in:
>> >> CPU: 2 PID: 12732 Comm: syz-executor6 Not tainted 4.11.0-rc3+ #365
>> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> >> task: ffff880062b7a2c0 task.stack: ffff880033480000
>> >> RIP: 0010:qdisc_hash_add.part.19+0xb6/0x3c0 net/sched/sch_api.c:280
>> >> RSP: 0018:ffff880033487820 EFLAGS: 00010202
>> >> RAX: dffffc0000000000 RBX: ffffffff85357e00 RCX: ffffc90002b24000
>> >> RDX: 000000000000007a RSI: ffffffff835a523a RDI: 00000000000003d0
>> >> RBP: ffff8800334878b8 R08: fffffbfff0a6afeb R09: fffffbfff0a6afeb
>> >> R10: 0000000000000001 R11: fffffbfff0a6afea R12: ffffffff85357e48
>> >> R13: 1ffff10006690f06 R14: ffff880033487890 R15: 0000000000000000
>> >> FS:  00007f68665d0700(0000) GS:ffff88006e200000(0000) knlGS:0000000000000000
>> >> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> >> CR2: 00000000004c2d44 CR3: 000000003c6f8000 CR4: 00000000000026e0
>> >> Call Trace:
>> >>  qdisc_hash_add+0x76/0x90 net/sched/sch_api.c:279
>> >>  attach_default_qdiscs net/sched/sch_generic.c:798 [inline]
>> >>  dev_activate+0x6ca/0x920 net/sched/sch_generic.c:829
>> >>  __dev_open+0x25b/0x360 net/core/dev.c:1348
>> >>  __dev_change_flags+0x159/0x3d0 net/core/dev.c:6460
>> >>  dev_change_flags+0x88/0x140 net/core/dev.c:6525
>> >>  dev_ifsioc+0x51f/0x9b0 net/core/dev_ioctl.c:254
>> >>  dev_ioctl+0x1fe/0x1030 net/core/dev_ioctl.c:532
>> >>  sock_do_ioctl+0x94/0xb0 net/socket.c:902
>> >>  sock_ioctl+0x2c2/0x440 net/socket.c:993
>> >>  vfs_ioctl fs/ioctl.c:45 [inline]
>> >>  do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
>> >>  SYSC_ioctl fs/ioctl.c:700 [inline]
>> >>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>> >>  entry_SYSCALL_64_fastpath+0x1f/0xc2
>> >
>> > The interesting part is why the NULL dereference is in
>> > qdisc_hash_add(), since we have a check before calling
>> > it:
>> >
>> > #ifdef CONFIG_NET_SCHED
>> >         if (dev->qdisc)
>> >                 qdisc_hash_add(dev->qdisc);
>> > #endif
>> >
>> >
>> > When attach_one_default_qdisc() fails, we should trigger
>> > the NULL pointer dereference bug at:
>> >
>> >     atomic_inc(&dev->qdisc->refcnt);
>>
>> I think qdisc is not NULL, it's something _in_ qdisc that is NULL. The
>> crash happens here:
>>
>>                 struct Qdisc *root = qdisc_dev(q)->qdisc;
>>
>> so it's probably device.
>
>
>
> Looks like this bug came with commit 59cc1f61f09c
> ("net: sched: convert qdisc linked list to hashtable")
>
> I would simply guard qdisc_hash_add()
>
> (Against &noop_qdisc)

Yeah, I missed that dev_init_scheduler() could assign noop_qdisc
to each tx queue. Then the check in attach_default_qdiscs()
is always false? If so we need...

 #ifdef CONFIG_NET_SCHED
-       if (dev->qdisc)
+       if (dev->qdisc != &noop_qdisc)
                qdisc_hash_add(dev->qdisc);
 #endif

^ permalink raw reply	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2017-03-24 17:28 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2017-03-23 16:06 net/sched: GPF in qdisc_hash_add Dmitry Vyukov
2017-03-23 19:00 ` Cong Wang
2017-03-23 19:06   ` Dmitry Vyukov
2017-03-23 19:10     ` Eric Dumazet
2017-03-24 17:28       ` Cong Wang

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