Re: Sound: BUG: KASAN: use-after-free in kill_fasync

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On 2016/4/6 19:37, Baozeng Ding wrote:



On 2016/4/5 22:18, Takashi Iwai wrote:

On Tue, 05 Apr 2016 15:51:30 +0200,
Baozeng Ding wrote:

Hi all,
I've got the following report (use-after-free in kill_fasync) while
running syzkaller.
Unfortunately no reproducer.The kernel version is 4.5 (on Mar 16 commit
09fd671ccb2475436bd5f597f751ca4a7d177aea).

==================================================================
BUG: KASAN: use-after-free in kill_fasync+0x3fb/0x420 at addr
ffff880067691d88
Read of size 8 by task swapper/2/0
============================================================================= 
BUG kmalloc-2048 (Not tainted): kasan: bad access detected
----------------------------------------------------------------------------- 

Disabling lock debugging due to kernel taint
INFO: Allocated in 0xbbbbbbbbbbbbbbbb age=18446678412249576073
cpu=2245704320 pid=-1
[<     inline     >] kmalloc /kernel/include/linux/slab.h:472
[<     inline     >] kzalloc /kernel/include/linux/slab.h:616
[<      none      >] snd_pcm_attach_substream+0x3b4/0xb10
/kernel/sound/core/pcm.c:966
[<      none      >] ___slab_alloc+0x4c7/0x500 /kernel/mm/slub.c:2446
[<      none      >] __slab_alloc+0x4c/0x90 /kernel/mm/slub.c:2475
[<     inline     >] slab_alloc_node /kernel/mm/slub.c:2538
[<     inline     >] slab_alloc /kernel/mm/slub.c:2580
[<      none      >] kmem_cache_alloc_trace+0x262/0x300
/kernel/mm/slub.c:2597
[<     inline     >] kmalloc /kernel/include/linux/slab.h:472
[<     inline     >] kzalloc /kernel/include/linux/slab.h:616
[<      none      >] snd_pcm_attach_substream+0x3b4/0xb10
/kernel/sound/core/pcm.c:966
[<      none      >] snd_pcm_open_substream+0x84/0x450
/kernel/sound/core/pcm_native.c:2262
[<     inline     >] snd_pcm_oss_open_file
/kernel/sound/core/oss/pcm_oss.c:2346
[<      none      >] snd_pcm_oss_open.part.17+0x5a4/0x1100
/kernel/sound/core/oss/pcm_oss.c:2428
[<      none      >] snd_pcm_oss_open+0x35/0x50
/kernel/sound/core/oss/pcm_oss.c:2392
[<      none      >] soundcore_open+0x30f/0x640
/kernel/sound/sound_core.c:639
[<      none      >] chrdev_open+0x22a/0x4c0 /kernel/fs/char_dev.c:388
[<      none      >] do_dentry_open+0x6a2/0xcb0 /kernel/fs/open.c:736
[<      none      >] vfs_open+0x17b/0x1f0 /kernel/fs/open.c:853
[<     inline     >] do_last /kernel/fs/namei.c:3258
[<      none      >] path_openat+0x4837/0x5830 /kernel/fs/namei.c:3394
[<      none      >] do_filp_open+0x18e/0x250 /kernel/fs/namei.c:3429
[<      none      >] do_sys_open+0x201/0x420 /kernel/fs/open.c:1022
[<     inline     >] SYSC_open /kernel/fs/open.c:1040
[<      none      >] SyS_open+0x2d/0x40 /kernel/fs/open.c:1035
INFO: Freed in 0x10000b076 age=18446678416544543380 cpu=0 pid=0
[<      none      >] snd_pcm_detach_substream+0x134/0x280
/kernel/sound/core/pcm.c:1017
[<      none      >] __slab_free+0x1e8/0x300 /kernel/mm/slub.c:2657
[<     inline     >] slab_free /kernel/mm/slub.c:2810
[<      none      >] kfree+0x24e/0x2d0 /kernel/mm/slub.c:3661
[<      none      >] snd_pcm_detach_substream+0x134/0x280
/kernel/sound/core/pcm.c:1017
[<      none      >] snd_pcm_release_substream.part.38+0x219/0x2f0
/kernel/sound/core/pcm_native.c:2250
[<      none      >] snd_pcm_release_substream+0x59/0x70
/kernel/sound/core/pcm_native.c:2251
[<      none      >] snd_pcm_oss_release_file+0x45/0xb0
/kernel/sound/core/oss/pcm_oss.c:2305
[<      none      >] snd_pcm_oss_release+0xfa/0x250
/kernel/sound/core/oss/pcm_oss.c:2485
[<      none      >] __fput+0x236/0x780 /kernel/fs/file_table.c:208
[<      none      >] ____fput+0x15/0x20 /kernel/fs/file_table.c:244
[<      none      >] task_work_run+0x16b/0x200
/kernel/kernel/task_work.c:115
[< inline >] exit_task_work /kernel/include/linux/task_work.h:21 
[<      none      >] do_exit+0x87f/0x2c90 /kernel/kernel/exit.c:748
[< none >] do_group_exit+0x108/0x330 /kernel/kernel/exit.c:878 
[<     inline     >] SYSC_exit_group /kernel/kernel/exit.c:889
[<      none      >] SyS_exit_group+0x1d/0x20 /kernel/kernel/exit.c:887
[<      none      >] entry_SYSCALL_64_fastpath+0x23/0xc1
/kernel/arch/x86/entry/entry_64.S:207
INFO: Slab 0xffffea00019da400 objects=13 used=8 fp=0xffff880067691be0
flags=0x5fffc0000004080
INFO: Object 0xffff880067691bd8 @offset=7128 fp=0xbbbbbbbbbbbbbbbb
Call Trace:
   <IRQ>  [<     inline     >] __dump_stack /kernel/lib/dump_stack.c:15
   <IRQ>  [<ffffffff82945051>] dump_stack+0xb3/0x112
/kernel/lib/dump_stack.c:51
   [<ffffffff817009ad>] print_trailer+0x10d/0x190 /kernel/mm/slub.c:668
   [<ffffffff817074af>] object_err+0x2f/0x40 /kernel/mm/slub.c:675
   [<     inline     >] print_address_description
/kernel/mm/kasan/report.c:138
   [<ffffffff81709ca5>] kasan_report_error+0x215/0x530
/kernel/mm/kasan/report.c:236
[< inline >] ? spin_lock /kernel/include/linux/spinlock.h:302 
   [<ffffffff84a1c550>] ? snd_pcm_stream_lock+0x80/0xd0
/kernel/sound/core/pcm_native.c:104
   [<     inline     >] kasan_report /kernel/mm/kasan/report.c:259
   [<ffffffff8170a0be>] __asan_report_load8_noabort+0x3e/0x40
/kernel/mm/kasan/report.c:280
[<ffffffff81792a0b>] ? kill_fasync+0x3fb/0x420 /kernel/fs/fcntl.c:729 
   [<ffffffff81792a0b>] kill_fasync+0x3fb/0x420 /kernel/fs/fcntl.c:729
   [<ffffffff84a36e08>] snd_pcm_period_elapsed+0x1c8/0x230
/kernel/sound/core/pcm_lib.c:1890
   [<ffffffff84b6e2e0>] ? get_bound_vga.isra.21.part.22+0x140/0x140
/kernel/sound/pci/hda/hda_intel.c:1327
   [<ffffffff84b0637d>] stream_update+0xad/0xe0
/kernel/sound/pci/hda/hda_controller.c:923
   [<ffffffff84c1583e>] snd_hdac_bus_handle_stream_irq+0x24e/0x350
/kernel/sound/hda/hdac_controller.c:449
   [<ffffffff84b062d0>] ? azx_init_chip+0x100/0x100
/kernel/sound/pci/hda/hda_controller.c:890
   [<ffffffff84b04d24>] ? azx_interrupt+0x14/0x4d0
/kernel/sound/pci/hda/hda_controller.c:929
   [<ffffffff84b04eee>] azx_interrupt+0x1de/0x4d0
/kernel/sound/pci/hda/hda_controller.c:954
   [<ffffffff84b04d10>] ? azx_stop_chip+0x20/0x20
/kernel/sound/pci/hda/hda_controller.c:908
   [<ffffffff8143d9e3>] handle_irq_event_percpu+0xf3/0x790
/kernel/kernel/irq/handle.c:145
   [<ffffffff8143e127>] handle_irq_event+0xa7/0x140
/kernel/kernel/irq/handle.c:192
   [<ffffffff81447f81>] handle_edge_irq+0x1e1/0x8d0
/kernel/kernel/irq/chip.c:623
   [<     inline     >] generic_handle_irq_desc
/kernel/include/linux/irqdesc.h:146
   [<ffffffff811ad739>] handle_irq+0x109/0x2a0
/kernel/arch/x86/kernel/irq_64.c:78
   [<     inline     >] ? rcu_lock_release
/kernel/include/linux/rcupdate.h:491
   [<     inline     >] ? rcu_read_unlock
/kernel/include/linux/rcupdate.h:926
   [<     inline     >] ? __atomic_notifier_call_chain
/kernel/kernel/notifier.c:184
   [<ffffffff81369c4f>] ? atomic_notifier_call_chain+0xbf/0x140
/kernel/kernel/notifier.c:193
   [<ffffffff81369b90>] ? __atomic_notifier_call_chain+0x150/0x150
/kernel/include/linux/rcupdate.h:922
[<ffffffff811ac36d>] do_IRQ+0x7d/0x1a0 /kernel/arch/x86/kernel/irq.c:240 
   [<ffffffff85dac40c>] common_interrupt+0x8c/0x8c
/kernel/arch/x86/entry/entry_64.S:454
   <EOI>  [<ffffffff812245c6>] ? native_safe_halt+0x6/0x10
/kernel/./arch/x86/include/asm/irqflags.h:49
   [<ffffffff81405ced>] ? trace_hardirqs_on+0xd/0x10
/kernel/kernel/locking/lockdep.c:2635
   [<     inline     >] arch_safe_halt
/kernel/./arch/x86/include/asm/paravirt.h:117
   [<ffffffff811bf152>] default_idle+0x22/0x2d0
/kernel/arch/x86/kernel/process.c:307
   [<ffffffff811c053a>] arch_cpu_idle+0xa/0x10
/kernel/arch/x86/kernel/process.c:298
   [<ffffffff813eb618>] default_idle_call+0x48/0x70
/kernel/kernel/sched/idle.c:93
[< inline >] cpuidle_idle_call /kernel/kernel/sched/idle.c:151 
   [<     inline     >] cpu_idle_loop /kernel/kernel/sched/idle.c:242
   [<ffffffff813ebaa7>] cpu_startup_entry+0x467/0x600
/kernel/kernel/sched/idle.c:291
   [<ffffffff81201432>] start_secondary+0x2b2/0x380
/kernel/arch/x86/kernel/smpboot.c:259
   [<ffffffff81201180>] ? set_cpu_sibling_map+0x18a0/0x18a0
/kernel/include/linux/topology.h:80
Memory state around the buggy address:
   ffff880067691c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
   ffff880067691d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  >ffff880067691d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                        ^
   ffff880067691e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
   ffff880067691e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
It seems that in function snd_pcm_detach_substream, when freeing runtime 
structure, it did not handle its fasync
data pointer. Any ideas? Thanks.

Well, fasync doesn't need a cleanup usually.  Do you have a proper
reproducer code?
Sorry, I cannot reproduce it. I will apply your patch and test it. I will tell you the result whether it is okay a few days later. 
Thanks.


In anyway, try the patch below.  I'm not sure whether this would help,
but if the path is via kill_fasync(), it'd be good to put in the
protected context.
During the last few weeks, I have not seen the bug any more after applying your patch. Thanks. 

Takashi

---
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 3a9b66c6e09c..0aca39762ed0 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1886,8 +1886,8 @@ void snd_pcm_period_elapsed(struct snd_pcm_substream *substream) 
          snd_timer_interrupt(substream->timer, 1);
  #endif
   _end:
-    snd_pcm_stream_unlock_irqrestore(substream, flags);
      kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
+    snd_pcm_stream_unlock_irqrestore(substream, flags);
  }
    EXPORT_SYMBOL(snd_pcm_period_elapsed);




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