CIFS: Fix task struct use-after-free on reconnect
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Message ID 20200123160906.28498-1-vincent.whitchurch@axis.com
State New
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  • CIFS: Fix task struct use-after-free on reconnect
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Commit Message

Vincent Whitchurch Jan. 23, 2020, 4:09 p.m. UTC
The task which created the MID may be gone by the time cifsd attempts to
call the callbacks on MIDs from cifs_reconnect().

This leads to a use-after-free of the task struct in cifs_wake_up_task:

 ==================================================================
 BUG: KASAN: use-after-free in __lock_acquire+0x31a0/0x3270
 Read of size 8 at addr ffff8880103e3a68 by task cifsd/630

 CPU: 0 PID: 630 Comm: cifsd Not tainted 5.5.0-rc6+ #119
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
 Call Trace:
  dump_stack+0x8e/0xcb
  print_address_description.constprop.5+0x1d3/0x3c0
  ? __lock_acquire+0x31a0/0x3270
  __kasan_report+0x152/0x1aa
  ? __lock_acquire+0x31a0/0x3270
  ? __lock_acquire+0x31a0/0x3270
  kasan_report+0xe/0x20
  __lock_acquire+0x31a0/0x3270
  ? __wake_up_common+0x1dc/0x630
  ? _raw_spin_unlock_irqrestore+0x4c/0x60
  ? mark_held_locks+0xf0/0xf0
  ? _raw_spin_unlock_irqrestore+0x39/0x60
  ? __wake_up_common_lock+0xd5/0x130
  ? __wake_up_common+0x630/0x630
  lock_acquire+0x13f/0x330
  ? try_to_wake_up+0xa3/0x19e0
  _raw_spin_lock_irqsave+0x38/0x50
  ? try_to_wake_up+0xa3/0x19e0
  try_to_wake_up+0xa3/0x19e0
  ? cifs_compound_callback+0x178/0x210
  ? set_cpus_allowed_ptr+0x10/0x10
  cifs_reconnect+0xa1c/0x15d0
  ? generic_ip_connect+0x1860/0x1860
  ? rwlock_bug.part.0+0x90/0x90
  cifs_readv_from_socket+0x479/0x690
  cifs_read_from_socket+0x9d/0xe0
  ? cifs_readv_from_socket+0x690/0x690
  ? mempool_resize+0x690/0x690
  ? rwlock_bug.part.0+0x90/0x90
  ? memset+0x1f/0x40
  ? allocate_buffers+0xff/0x340
  cifs_demultiplex_thread+0x388/0x2a50
  ? cifs_handle_standard+0x610/0x610
  ? rcu_read_lock_held_common+0x120/0x120
  ? mark_lock+0x11b/0xc00
  ? __lock_acquire+0x14ed/0x3270
  ? __kthread_parkme+0x78/0x100
  ? lockdep_hardirqs_on+0x3e8/0x560
  ? lock_downgrade+0x6a0/0x6a0
  ? lockdep_hardirqs_on+0x3e8/0x560
  ? _raw_spin_unlock_irqrestore+0x39/0x60
  ? cifs_handle_standard+0x610/0x610
  kthread+0x2bb/0x3a0
  ? kthread_create_worker_on_cpu+0xc0/0xc0
  ret_from_fork+0x3a/0x50

 Allocated by task 649:
  save_stack+0x19/0x70
  __kasan_kmalloc.constprop.5+0xa6/0xf0
  kmem_cache_alloc+0x107/0x320
  copy_process+0x17bc/0x5370
  _do_fork+0x103/0xbf0
  __x64_sys_clone+0x168/0x1e0
  do_syscall_64+0x9b/0xec0
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

 Freed by task 0:
  save_stack+0x19/0x70
  __kasan_slab_free+0x11d/0x160
  kmem_cache_free+0xb5/0x3d0
  rcu_core+0x52f/0x1230
  __do_softirq+0x24d/0x962

 The buggy address belongs to the object at ffff8880103e32c0
  which belongs to the cache task_struct of size 6016
 The buggy address is located 1960 bytes inside of
  6016-byte region [ffff8880103e32c0, ffff8880103e4a40)
 The buggy address belongs to the page:
 page:ffffea000040f800 refcount:1 mapcount:0 mapping:ffff8880108da5c0
 index:0xffff8880103e4c00 compound_mapcount: 0
 raw: 4000000000010200 ffffea00001f2208 ffffea00001e3408 ffff8880108da5c0
 raw: ffff8880103e4c00 0000000000050003 00000001ffffffff 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  ffff8880103e3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880103e3980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 >ffff8880103e3a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                           ^
  ffff8880103e3a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880103e3b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ==================================================================

This can be reliably reproduced by adding the below delay to
cifs_reconnect(), running find(1) on the mount, restarting the samba
server while find is running, and killing find during the delay:

  	spin_unlock(&GlobalMid_Lock);
  	mutex_unlock(&server->srv_mutex);

 +	msleep(10000);
 +
  	cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
  	list_for_each_safe(tmp, tmp2, &retry_list) {
  		mid_entry = list_entry(tmp, struct mid_q_entry, qhead);

Fix this by holding a reference to the task struct until the MID is
freed.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
---
 fs/cifs/cifsglob.h      | 1 +
 fs/cifs/smb2transport.c | 2 ++
 fs/cifs/transport.c     | 3 +++
 3 files changed, 6 insertions(+)

Comments

Vincent Whitchurch Jan. 23, 2020, 5:01 p.m. UTC | #1
On Thu, Jan 23, 2020 at 05:35:16PM +0100, Steve French wrote:
> On Thu, Jan 23, 2020, 10:17 Vincent Whitchurch <vincent.whitchurch@axis.com> wrote:
> > This can be reliably reproduced by adding the below delay to
> > cifs_reconnect(), running find(1) on the mount, restarting the samba
> > server while find is running, and killing find during the delay:
> > 
> >         spin_unlock(&GlobalMid_Lock);
> >         mutex_unlock(&server->srv_mutex);
> > 
> >  +      msleep(10000);
> >  +
> >         cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
> >         list_for_each_safe(tmp, tmp2, &retry_list) {
> >                 mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
> > 
> > Fix this by holding a reference to the task struct until the MID is
> > freed.
> 
> Cc:stable as well?

Yes, I think this bug has been there for a while.

Note that the test described above usually triggers a different crash on
kernels earlier than v5.4 because abe57073d08c13b95a46ccf48c ("CIFS: Fix
retry mid list corruption on reconnects") has not (yet?) been backported
to those stable kernels.
Paulo Alcantara Jan. 23, 2020, 5:07 p.m. UTC | #2
Vincent Whitchurch <vincent.whitchurch@axis.com> writes:

> The task which created the MID may be gone by the time cifsd attempts to
> call the callbacks on MIDs from cifs_reconnect().
>
> This leads to a use-after-free of the task struct in cifs_wake_up_task:
>
>  ==================================================================
>  BUG: KASAN: use-after-free in __lock_acquire+0x31a0/0x3270
>  Read of size 8 at addr ffff8880103e3a68 by task cifsd/630
>
>  CPU: 0 PID: 630 Comm: cifsd Not tainted 5.5.0-rc6+ #119
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>  Call Trace:
>   dump_stack+0x8e/0xcb
>   print_address_description.constprop.5+0x1d3/0x3c0
>   ? __lock_acquire+0x31a0/0x3270
>   __kasan_report+0x152/0x1aa
>   ? __lock_acquire+0x31a0/0x3270
>   ? __lock_acquire+0x31a0/0x3270
>   kasan_report+0xe/0x20
>   __lock_acquire+0x31a0/0x3270
>   ? __wake_up_common+0x1dc/0x630
>   ? _raw_spin_unlock_irqrestore+0x4c/0x60
>   ? mark_held_locks+0xf0/0xf0
>   ? _raw_spin_unlock_irqrestore+0x39/0x60
>   ? __wake_up_common_lock+0xd5/0x130
>   ? __wake_up_common+0x630/0x630
>   lock_acquire+0x13f/0x330
>   ? try_to_wake_up+0xa3/0x19e0
>   _raw_spin_lock_irqsave+0x38/0x50
>   ? try_to_wake_up+0xa3/0x19e0
>   try_to_wake_up+0xa3/0x19e0
>   ? cifs_compound_callback+0x178/0x210
>   ? set_cpus_allowed_ptr+0x10/0x10
>   cifs_reconnect+0xa1c/0x15d0
>   ? generic_ip_connect+0x1860/0x1860
>   ? rwlock_bug.part.0+0x90/0x90
>   cifs_readv_from_socket+0x479/0x690
>   cifs_read_from_socket+0x9d/0xe0
>   ? cifs_readv_from_socket+0x690/0x690
>   ? mempool_resize+0x690/0x690
>   ? rwlock_bug.part.0+0x90/0x90
>   ? memset+0x1f/0x40
>   ? allocate_buffers+0xff/0x340
>   cifs_demultiplex_thread+0x388/0x2a50
>   ? cifs_handle_standard+0x610/0x610
>   ? rcu_read_lock_held_common+0x120/0x120
>   ? mark_lock+0x11b/0xc00
>   ? __lock_acquire+0x14ed/0x3270
>   ? __kthread_parkme+0x78/0x100
>   ? lockdep_hardirqs_on+0x3e8/0x560
>   ? lock_downgrade+0x6a0/0x6a0
>   ? lockdep_hardirqs_on+0x3e8/0x560
>   ? _raw_spin_unlock_irqrestore+0x39/0x60
>   ? cifs_handle_standard+0x610/0x610
>   kthread+0x2bb/0x3a0
>   ? kthread_create_worker_on_cpu+0xc0/0xc0
>   ret_from_fork+0x3a/0x50
>
>  Allocated by task 649:
>   save_stack+0x19/0x70
>   __kasan_kmalloc.constprop.5+0xa6/0xf0
>   kmem_cache_alloc+0x107/0x320
>   copy_process+0x17bc/0x5370
>   _do_fork+0x103/0xbf0
>   __x64_sys_clone+0x168/0x1e0
>   do_syscall_64+0x9b/0xec0
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
>  Freed by task 0:
>   save_stack+0x19/0x70
>   __kasan_slab_free+0x11d/0x160
>   kmem_cache_free+0xb5/0x3d0
>   rcu_core+0x52f/0x1230
>   __do_softirq+0x24d/0x962
>
>  The buggy address belongs to the object at ffff8880103e32c0
>   which belongs to the cache task_struct of size 6016
>  The buggy address is located 1960 bytes inside of
>   6016-byte region [ffff8880103e32c0, ffff8880103e4a40)
>  The buggy address belongs to the page:
>  page:ffffea000040f800 refcount:1 mapcount:0 mapping:ffff8880108da5c0
>  index:0xffff8880103e4c00 compound_mapcount: 0
>  raw: 4000000000010200 ffffea00001f2208 ffffea00001e3408 ffff8880108da5c0
>  raw: ffff8880103e4c00 0000000000050003 00000001ffffffff 0000000000000000
>  page dumped because: kasan: bad access detected
>
>  Memory state around the buggy address:
>   ffff8880103e3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8880103e3980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  >ffff8880103e3a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                            ^
>   ffff8880103e3a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8880103e3b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ==================================================================
>
> This can be reliably reproduced by adding the below delay to
> cifs_reconnect(), running find(1) on the mount, restarting the samba
> server while find is running, and killing find during the delay:
>
>   	spin_unlock(&GlobalMid_Lock);
>   	mutex_unlock(&server->srv_mutex);
>
>  +	msleep(10000);
>  +
>   	cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
>   	list_for_each_safe(tmp, tmp2, &retry_list) {
>   		mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
>
> Fix this by holding a reference to the task struct until the MID is
> freed.
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> ---
>  fs/cifs/cifsglob.h      | 1 +
>  fs/cifs/smb2transport.c | 2 ++
>  fs/cifs/transport.c     | 3 +++
>  3 files changed, 6 insertions(+)

Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>

Thanks,
Paulo
Pavel Shilovsky Jan. 23, 2020, 6:47 p.m. UTC | #3
чт, 23 янв. 2020 г. в 09:02, Vincent Whitchurch <vincent.whitchurch@axis.com>:
>
> On Thu, Jan 23, 2020 at 05:35:16PM +0100, Steve French wrote:
> > On Thu, Jan 23, 2020, 10:17 Vincent Whitchurch <vincent.whitchurch@axis.com> wrote:
> > > This can be reliably reproduced by adding the below delay to
> > > cifs_reconnect(), running find(1) on the mount, restarting the samba
> > > server while find is running, and killing find during the delay:
> > >
> > >         spin_unlock(&GlobalMid_Lock);
> > >         mutex_unlock(&server->srv_mutex);
> > >
> > >  +      msleep(10000);
> > >  +
> > >         cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
> > >         list_for_each_safe(tmp, tmp2, &retry_list) {
> > >                 mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
> > >
> > > Fix this by holding a reference to the task struct until the MID is
> > > freed.
> >
> > Cc:stable as well?
>
> Yes, I think this bug has been there for a while.
>
> Note that the test described above usually triggers a different crash on
> kernels earlier than v5.4 because abe57073d08c13b95a46ccf48c ("CIFS: Fix
> retry mid list corruption on reconnects") has not (yet?) been backported
> to those stable kernels.

It has been only backported to 5.3.x - available from version 5.3.10.

The patch in the thread looks good. Good catch, thanks!

Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>

--
Best regards,
Pavel Shilovsky
Steve French Jan. 23, 2020, 8:20 p.m. UTC | #4
merged into cifs-2.6.git for-next (and added cc:stable)

On Thu, Jan 23, 2020 at 10:17 AM Vincent Whitchurch
<vincent.whitchurch@axis.com> wrote:
>
> The task which created the MID may be gone by the time cifsd attempts to
> call the callbacks on MIDs from cifs_reconnect().
>
> This leads to a use-after-free of the task struct in cifs_wake_up_task:
>
>  ==================================================================
>  BUG: KASAN: use-after-free in __lock_acquire+0x31a0/0x3270
>  Read of size 8 at addr ffff8880103e3a68 by task cifsd/630
>
>  CPU: 0 PID: 630 Comm: cifsd Not tainted 5.5.0-rc6+ #119
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>  Call Trace:
>   dump_stack+0x8e/0xcb
>   print_address_description.constprop.5+0x1d3/0x3c0
>   ? __lock_acquire+0x31a0/0x3270
>   __kasan_report+0x152/0x1aa
>   ? __lock_acquire+0x31a0/0x3270
>   ? __lock_acquire+0x31a0/0x3270
>   kasan_report+0xe/0x20
>   __lock_acquire+0x31a0/0x3270
>   ? __wake_up_common+0x1dc/0x630
>   ? _raw_spin_unlock_irqrestore+0x4c/0x60
>   ? mark_held_locks+0xf0/0xf0
>   ? _raw_spin_unlock_irqrestore+0x39/0x60
>   ? __wake_up_common_lock+0xd5/0x130
>   ? __wake_up_common+0x630/0x630
>   lock_acquire+0x13f/0x330
>   ? try_to_wake_up+0xa3/0x19e0
>   _raw_spin_lock_irqsave+0x38/0x50
>   ? try_to_wake_up+0xa3/0x19e0
>   try_to_wake_up+0xa3/0x19e0
>   ? cifs_compound_callback+0x178/0x210
>   ? set_cpus_allowed_ptr+0x10/0x10
>   cifs_reconnect+0xa1c/0x15d0
>   ? generic_ip_connect+0x1860/0x1860
>   ? rwlock_bug.part.0+0x90/0x90
>   cifs_readv_from_socket+0x479/0x690
>   cifs_read_from_socket+0x9d/0xe0
>   ? cifs_readv_from_socket+0x690/0x690
>   ? mempool_resize+0x690/0x690
>   ? rwlock_bug.part.0+0x90/0x90
>   ? memset+0x1f/0x40
>   ? allocate_buffers+0xff/0x340
>   cifs_demultiplex_thread+0x388/0x2a50
>   ? cifs_handle_standard+0x610/0x610
>   ? rcu_read_lock_held_common+0x120/0x120
>   ? mark_lock+0x11b/0xc00
>   ? __lock_acquire+0x14ed/0x3270
>   ? __kthread_parkme+0x78/0x100
>   ? lockdep_hardirqs_on+0x3e8/0x560
>   ? lock_downgrade+0x6a0/0x6a0
>   ? lockdep_hardirqs_on+0x3e8/0x560
>   ? _raw_spin_unlock_irqrestore+0x39/0x60
>   ? cifs_handle_standard+0x610/0x610
>   kthread+0x2bb/0x3a0
>   ? kthread_create_worker_on_cpu+0xc0/0xc0
>   ret_from_fork+0x3a/0x50
>
>  Allocated by task 649:
>   save_stack+0x19/0x70
>   __kasan_kmalloc.constprop.5+0xa6/0xf0
>   kmem_cache_alloc+0x107/0x320
>   copy_process+0x17bc/0x5370
>   _do_fork+0x103/0xbf0
>   __x64_sys_clone+0x168/0x1e0
>   do_syscall_64+0x9b/0xec0
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
>  Freed by task 0:
>   save_stack+0x19/0x70
>   __kasan_slab_free+0x11d/0x160
>   kmem_cache_free+0xb5/0x3d0
>   rcu_core+0x52f/0x1230
>   __do_softirq+0x24d/0x962
>
>  The buggy address belongs to the object at ffff8880103e32c0
>   which belongs to the cache task_struct of size 6016
>  The buggy address is located 1960 bytes inside of
>   6016-byte region [ffff8880103e32c0, ffff8880103e4a40)
>  The buggy address belongs to the page:
>  page:ffffea000040f800 refcount:1 mapcount:0 mapping:ffff8880108da5c0
>  index:0xffff8880103e4c00 compound_mapcount: 0
>  raw: 4000000000010200 ffffea00001f2208 ffffea00001e3408 ffff8880108da5c0
>  raw: ffff8880103e4c00 0000000000050003 00000001ffffffff 0000000000000000
>  page dumped because: kasan: bad access detected
>
>  Memory state around the buggy address:
>   ffff8880103e3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8880103e3980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  >ffff8880103e3a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                            ^
>   ffff8880103e3a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8880103e3b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ==================================================================
>
> This can be reliably reproduced by adding the below delay to
> cifs_reconnect(), running find(1) on the mount, restarting the samba
> server while find is running, and killing find during the delay:
>
>         spin_unlock(&GlobalMid_Lock);
>         mutex_unlock(&server->srv_mutex);
>
>  +      msleep(10000);
>  +
>         cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
>         list_for_each_safe(tmp, tmp2, &retry_list) {
>                 mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
>
> Fix this by holding a reference to the task struct until the MID is
> freed.
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> ---
>  fs/cifs/cifsglob.h      | 1 +
>  fs/cifs/smb2transport.c | 2 ++
>  fs/cifs/transport.c     | 3 +++
>  3 files changed, 6 insertions(+)
>
> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> index 40705e862451..239338d57086 100644
> --- a/fs/cifs/cifsglob.h
> +++ b/fs/cifs/cifsglob.h
> @@ -1588,6 +1588,7 @@ struct mid_q_entry {
>         mid_callback_t *callback; /* call completion callback */
>         mid_handle_t *handle; /* call handle mid callback */
>         void *callback_data;      /* general purpose pointer for callback */
> +       struct task_struct *creator;
>         void *resp_buf;         /* pointer to received SMB header */
>         unsigned int resp_buf_size;
>         int mid_state;  /* wish this were enum but can not pass to wait_event */
> diff --git a/fs/cifs/smb2transport.c b/fs/cifs/smb2transport.c
> index 387c88704c52..fe6acfce3390 100644
> --- a/fs/cifs/smb2transport.c
> +++ b/fs/cifs/smb2transport.c
> @@ -685,6 +685,8 @@ smb2_mid_entry_alloc(const struct smb2_sync_hdr *shdr,
>          * The default is for the mid to be synchronous, so the
>          * default callback just wakes up the current task.
>          */
> +       get_task_struct(current);
> +       temp->creator = current;
>         temp->callback = cifs_wake_up_task;
>         temp->callback_data = current;
>
> diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
> index 3d2e11f85cba..cb3ee916f527 100644
> --- a/fs/cifs/transport.c
> +++ b/fs/cifs/transport.c
> @@ -76,6 +76,8 @@ AllocMidQEntry(const struct smb_hdr *smb_buffer, struct TCP_Server_Info *server)
>          * The default is for the mid to be synchronous, so the
>          * default callback just wakes up the current task.
>          */
> +       get_task_struct(current);
> +       temp->creator = current;
>         temp->callback = cifs_wake_up_task;
>         temp->callback_data = current;
>
> @@ -158,6 +160,7 @@ static void _cifs_mid_q_entry_release(struct kref *refcount)
>                 }
>         }
>  #endif
> +       put_task_struct(midEntry->creator);
>
>         mempool_free(midEntry, cifs_mid_poolp);
>  }
> --
> 2.20.0
>

Patch
diff mbox series

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 40705e862451..239338d57086 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -1588,6 +1588,7 @@  struct mid_q_entry {
 	mid_callback_t *callback; /* call completion callback */
 	mid_handle_t *handle; /* call handle mid callback */
 	void *callback_data;	  /* general purpose pointer for callback */
+	struct task_struct *creator;
 	void *resp_buf;		/* pointer to received SMB header */
 	unsigned int resp_buf_size;
 	int mid_state;	/* wish this were enum but can not pass to wait_event */
diff --git a/fs/cifs/smb2transport.c b/fs/cifs/smb2transport.c
index 387c88704c52..fe6acfce3390 100644
--- a/fs/cifs/smb2transport.c
+++ b/fs/cifs/smb2transport.c
@@ -685,6 +685,8 @@  smb2_mid_entry_alloc(const struct smb2_sync_hdr *shdr,
 	 * The default is for the mid to be synchronous, so the
 	 * default callback just wakes up the current task.
 	 */
+	get_task_struct(current);
+	temp->creator = current;
 	temp->callback = cifs_wake_up_task;
 	temp->callback_data = current;
 
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 3d2e11f85cba..cb3ee916f527 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -76,6 +76,8 @@  AllocMidQEntry(const struct smb_hdr *smb_buffer, struct TCP_Server_Info *server)
 	 * The default is for the mid to be synchronous, so the
 	 * default callback just wakes up the current task.
 	 */
+	get_task_struct(current);
+	temp->creator = current;
 	temp->callback = cifs_wake_up_task;
 	temp->callback_data = current;
 
@@ -158,6 +160,7 @@  static void _cifs_mid_q_entry_release(struct kref *refcount)
 		}
 	}
 #endif
+	put_task_struct(midEntry->creator);
 
 	mempool_free(midEntry, cifs_mid_poolp);
 }