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      CIFS: Fix task struct use-after-free on reconnect · f1f27ad7
      Vincent Whitchurch 提交于
      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: NVincent Whitchurch <vincent.whitchurch@axis.com>
      Signed-off-by: NSteve French <stfrench@microsoft.com>
      CC: Stable <stable@vger.kernel.org>
      Reviewed-by: NPaulo Alcantara (SUSE) <pc@cjr.nz>
      Reviewed-by: NPavel Shilovsky <pshilov@microsoft.com>
      f1f27ad7