• Vincent Whitchurch's avatar
    CIFS: Fix task struct use-after-free on reconnect · f1f27ad7
    Vincent Whitchurch authored
    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: default avatarVincent Whitchurch <vincent.whitchurch@axis.com>
    Signed-off-by: default avatarSteve French <stfrench@microsoft.com>
    CC: Stable <stable@vger.kernel.org>
    Reviewed-by: default avatarPaulo Alcantara (SUSE) <pc@cjr.nz>
    Reviewed-by: default avatarPavel Shilovsky <pshilov@microsoft.com>
    f1f27ad7
cifsglob.h 66.3 KB