Subject: Re: KASAN: slab-out-of-bounds Read in tun_net_xmit (2)

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 31 Dec 2018 10:51:43 +0100

Hi MST and Jason,

Could you please take a look at this?  This bug is caused by a thread
resizing the tun-queue (via tun_queue_resize -> ptr_ring_resize_multiple).
And error happens in tun_net_xmit -> ptr_ring_produce.  My guess is bug
happens when reading r->queue in ptr_ring_produce.

I've look at the code (see diff comments below), but I cannot spot the
issue as the (implicit) memory barrier of a spinlock should cover the
cases I can imagine.

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 6894976b54e3..75a262d274bb 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -107,6 +107,12 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
  */
 static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
 {
+       barrier(); // Compiler barrier, should not be needed as
+                  // spinlock are suppose-to-be a full barrier
+
+       // r->queue array can be kvfree'ed by ptr_ring_resize_multiple
+       // and reassigned by __ptr_ring_swap_queue, it should be safe
+       // as everything is called inder r->producer_lock spinlock.
        if (unlikely(!r->size) || r->queue[r->producer])
                return -ENOSPC;
 
@@ -578,6 +584,8 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
        r->consumer_head = 0;
        r->consumer_tail = 0;
        old = r->queue;
+       // Do we need some WRITE_ONCE for r->queue assignmment?
+       // or smp_wmb()
        r->queue = queue;
 
        return old;
@@ -640,6 +648,7 @@ static inline int ptr_ring_resize_multiple(struct ptr_ring **rings,
        for (i = 0; i < nrings; ++i) {
                spin_lock_irqsave(&(rings[i])->consumer_lock, flags);
                spin_lock(&(rings[i])->producer_lock);
+               // happens under lock(s)
                queues[i] = __ptr_ring_swap_queue(rings[i], queues[i],
                                                  size, gfp, destroy);
                spin_unlock(&(rings[i])->producer_lock);
@@ -647,7 +656,7 @@ static inline int ptr_ring_resize_multiple(struct ptr_ring **rings,
        }
 
        for (i = 0; i < nrings; ++i)
-               kvfree(queues[i]);
+               kvfree(queues[i]); // old r->queue is free'ed here
 
        kfree(queues);

On Sun, 30 Dec 2018 10:01:03 -0800
syzbot <[email-masked]> wrote:

> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    b71acb0e3721 Merge branch 'linus' of git://git.kernel.org/..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14494353400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4b137b8ba637eb77
> dashboard link: https://syzkaller.appspot.com/bug?extid=8993c0fa96d57c399735
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11a01577400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=174baeab400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: [email-masked]
> 
> IPv6: ADDRCONF(NETDEV_CHANGE): hsr0: link becomes ready
> IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
> 8021q: adding VLAN 0 to HW filter on device batadv0
> nf_conntrack: default automatic helper assignment has been turned off for  
> security reasons and CT-based  firewall rule not found. Use the iptables CT  
> target to attach helpers instead.
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in __ptr_ring_produce  
> include/linux/ptr_ring.h:110 [inline]
> BUG: KASAN: slab-out-of-bounds in ptr_ring_produce  
> include/linux/ptr_ring.h:133 [inline]
> BUG: KASAN: slab-out-of-bounds in tun_net_xmit+0x197e/0x1be0  
> drivers/net/tun.c:1119
> Read of size 8 at addr ffff88809fa64f48 by task swapper/0/0
> 
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.20.0+ #363
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
> Google 01/01/2011
> Call Trace:
>   <IRQ>
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x1d3/0x2c6 lib/dump_stack.c:113
>   print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
>   kasan_report_error mm/kasan/report.c:354 [inline]
>   kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
>   __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>   __ptr_ring_produce include/linux/ptr_ring.h:110 [inline]
>   ptr_ring_produce include/linux/ptr_ring.h:133 [inline]
>   tun_net_xmit+0x197e/0x1be0 drivers/net/tun.c:1119
>   __netdev_start_xmit include/linux/netdevice.h:4382 [inline]
>   netdev_start_xmit include/linux/netdevice.h:4391 [inline]
>   xmit_one net/core/dev.c:3278 [inline]
>   dev_hard_start_xmit+0x286/0xc80 net/core/dev.c:3294
>   sch_direct_xmit+0x48b/0x1130 net/sched/sch_generic.c:327
>   qdisc_restart net/sched/sch_generic.c:390 [inline]
>   __qdisc_run+0x624/0x19f0 net/sched/sch_generic.c:398
>   qdisc_run include/net/pkt_sched.h:121 [inline]
>   __dev_xmit_skb net/core/dev.c:3473 [inline]
>   __dev_queue_xmit+0x190c/0x3ac0 net/core/dev.c:3832
>   dev_queue_xmit+0x17/0x20 net/core/dev.c:3897
>   neigh_hh_output include/net/neighbour.h:498 [inline]
>   neigh_output include/net/neighbour.h:506 [inline]
>   ip6_finish_output2+0x144e/0x2930 net/ipv6/ip6_output.c:120
>   ip6_finish_output+0x583/0xc50 net/ipv6/ip6_output.c:154
>   NF_HOOK_COND include/linux/netfilter.h:278 [inline]
>   ip6_output+0x232/0x9d0 net/ipv6/ip6_output.c:171
>   dst_output include/net/dst.h:444 [inline]
>   NF_HOOK include/linux/netfilter.h:289 [inline]
>   mld_sendpack+0xac9/0xfa0 net/ipv6/mcast.c:1683
>   mld_send_initial_cr.part.32+0x114/0x160 net/ipv6/mcast.c:2100
>   mld_send_initial_cr net/ipv6/mcast.c:2084 [inline]
>   mld_dad_timer_expire+0x42/0x1b0 net/ipv6/mcast.c:2119
>   call_timer_fn+0x272/0x920 kernel/time/timer.c:1325
>   expire_timers kernel/time/timer.c:1362 [inline]
>   __run_timers+0x7e5/0xc70 kernel/time/timer.c:1681
>   run_timer_softirq+0x52/0xb0 kernel/time/timer.c:1694
>   __do_softirq+0x30c/0xb2e kernel/softirq.c:292
>   invoke_softirq kernel/softirq.c:373 [inline]
>   irq_exit+0x17f/0x1c0 kernel/softirq.c:413
>   exiting_irq arch/x86/include/asm/apic.h:536 [inline]
>   smp_apic_timer_interrupt+0x1cb/0x760 arch/x86/kernel/apic/apic.c:1062
>   apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807
>   </IRQ>
> RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:58
> Code: e9 2c ff ff ff 48 89 c7 48 89 45 d8 e8 a3 84 c9 f9 48 8b 45 d8 e9 ca  
> fe ff ff 48 89 df e8 92 84 c9 f9 eb 82 55 48 89 e5 fb f4 <5d> c3 0f 1f 84  
> 00 00 00 00 00 55 48 89 e5 f4 5d c3 90 90 90 90 90
> RSP: 0018:ffffffff89607c20 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
> RAX: dffffc0000000000 RBX: 1ffffffff12c0f88 RCX: 0000000000000000
> RDX: 1ffffffff12e4969 RSI: 0000000000000001 RDI: ffffffff89724b48
> RBP: ffffffff89607c20 R08: ffffffff8967aec0 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff89607ce0
> R13: ffffffff8a3a3260 R14: 0000000000000000 R15: 0000000000000000
>   arch_safe_halt arch/x86/include/asm/paravirt.h:156 [inline]
>   default_idle+0xbf/0x490 arch/x86/kernel/process.c:564
>   arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:555
>   default_idle_call+0x6d/0x90 kernel/sched/idle.c:93
>   cpuidle_idle_call kernel/sched/idle.c:153 [inline]
>   do_idle+0x3db/0x5b0 kernel/sched/idle.c:262
>   cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:353
>   rest_init+0x243/0x372 init/main.c:443
>   arch_call_rest_init+0xe/0x1b
>   start_kernel+0x873/0x8ae init/main.c:741
>   x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:470
>   x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:451
>   secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243
> 
> Allocated by task 7497:
>   save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>   set_track mm/kasan/kasan.c:460 [inline]
>   kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
>   __do_kmalloc_node mm/slab.c:3684 [inline]
>   __kmalloc_node+0x50/0x70 mm/slab.c:3691
>   kmalloc_node include/linux/slab.h:589 [inline]
>   kvmalloc_node+0x65/0xf0 mm/util.c:416
>   kvmalloc include/linux/mm.h:577 [inline]
>   kvmalloc_array include/linux/mm.h:595 [inline]
>   __ptr_ring_init_queue_alloc include/linux/ptr_ring.h:475 [inline]
>   ptr_ring_resize_multiple include/linux/ptr_ring.h:635 [inline]
>   tun_queue_resize drivers/net/tun.c:3606 [inline]
>   tun_device_event+0x56a/0x106c drivers/net/tun.c:3625
>   notifier_call_chain+0x17e/0x380 kernel/notifier.c:93
>   __raw_notifier_call_chain kernel/notifier.c:394 [inline]
>   raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
>   call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1739
>   call_netdevice_notifiers_extack net/core/dev.c:1751 [inline]
>   call_netdevice_notifiers net/core/dev.c:1765 [inline]
>   dev_change_tx_queue_len+0x188/0x270 net/core/dev.c:7742
>   dev_ifsioc+0x79b/0xa80 net/core/dev_ioctl.c:287
>   dev_ioctl+0x1b5/0xcc0 net/core/dev_ioctl.c:488
>   sock_do_ioctl+0x1f6/0x420 net/socket.c:973
>   sock_ioctl+0x313/0x690 net/socket.c:1074
>   vfs_ioctl fs/ioctl.c:46 [inline]
>   file_ioctl fs/ioctl.c:509 [inline]
>   do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
>   ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
>   __do_sys_ioctl fs/ioctl.c:720 [inline]
>   __se_sys_ioctl fs/ioctl.c:718 [inline]
>   __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
>   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 4400:
>   save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>   set_track mm/kasan/kasan.c:460 [inline]
>   __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
>   kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>   __cache_free mm/slab.c:3498 [inline]
>   kfree+0xcf/0x230 mm/slab.c:3817
>   single_release+0x8f/0xb0 fs/seq_file.c:597
>   __fput+0x385/0xa30 fs/file_table.c:278
>   ____fput+0x15/0x20 fs/file_table.c:309
>   task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
>   tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>   exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
>   prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>   syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>   do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> The buggy address belongs to the object at ffff88809fa64f40
>   which belongs to the cache kmalloc-32 of size 32
> The buggy address is located 8 bytes inside of
>   32-byte region [ffff88809fa64f40, ffff88809fa64f60)
> The buggy address belongs to the page:
> page:ffffea00027e9900 count:1 mapcount:0 mapping:ffff88812c3f01c0  
> index:0xffff88809fa64fc1
> flags: 0x1fffc0000000200(slab)
> raw: 01fffc0000000200 ffffea0002837048 ffffea00028f0888 ffff88812c3f01c0
> raw: ffff88809fa64fc1 ffff88809fa64000 000000010000003f 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>   ffff88809fa64e00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>   ffff88809fa64e80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
> > ffff88809fa64f00: fb fb fb fb fc fc fc fc 00 fc fc fc fc fc fc fc  
>                                                ^
>   ffff88809fa64f80: 06 fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>   ffff88809fa65000: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
> ==================================================================
> 

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer