1. 15 Feb, 2017 1 commit
    • Sahitya Tummala's avatar
      fuse: fix use after free issue in fuse_dev_do_read() · 6ba4d272
      Sahitya Tummala authored
      
      
      There is a potential race between fuse_dev_do_write()
      and request_wait_answer() contexts as shown below:
      
      TASK 1:
      __fuse_request_send():
        |--spin_lock(&fiq->waitq.lock);
        |--queue_request();
        |--spin_unlock(&fiq->waitq.lock);
        |--request_wait_answer():
             |--if (test_bit(FR_SENT, &req->flags))
             <gets pre-empted after it is validated true>
                                         TASK 2:
                                         fuse_dev_do_write():
                                           |--clears bit FR_SENT,
                                           |--request_end():
                                              |--sets bit FR_FINISHED
                                              |--spin_lock(&fiq->waitq.lock);
                                              |--list_del_init(&req->intr_entry);
                                              |--spin_unlock(&fiq->waitq.lock);
                                              |--fuse_put_request();
             |--queue_interrupt();
             <request gets queued to interrupts list>
                  |--wake_up_locked(&fiq->waitq);
             |--wait_event_freezable();
             <as FR_FINISHED is set, it returns and then
             the caller frees this request>
      
      Now, the next fuse_dev_do_read(), see interrupts list is not empty
      and then calls fuse_read_interrupt() which tries to access the request
      which is already free'd and gets the below crash:
      
      [11432.401266] Unable to handle kernel paging request at virtual address
      6b6b6b6b6b6b6b6b
      ...
      [11432.418518] Kernel BUG at ffffff80083720e0
      [11432.456168] PC is at __list_del_entry+0x6c/0xc4
      [11432.463573] LR is at fuse_dev_do_read+0x1ac/0x474
      ...
      [11432.679999] [<ffffff80083720e0>] __list_del_entry+0x6c/0xc4
      [11432.687794] [<ffffff80082c65e0>] fuse_dev_do_read+0x1ac/0x474
      [11432.693180] [<ffffff80082c6b14>] fuse_dev_read+0x6c/0x78
      [11432.699082] [<ffffff80081d5638>] __vfs_read+0xc0/0xe8
      [11432.704459] [<ffffff80081d5efc>] vfs_read+0x90/0x108
      [11432.709406] [<ffffff80081d67f0>] SyS_read+0x58/0x94
      
      As FR_FINISHED bit is set before deleting the intr_entry with input
      queue lock in request completion path, do the testing of this flag and
      queueing atomically with the same lock in queue_interrupt().
      Signed-off-by: default avatarSahitya Tummala <stummala@codeaurora.org>
      Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
      Fixes: fd22d62e ("fuse: no fc->lock for iqueue parts")
      Cc: <stable@vger.kernel.org> # 4.2+
      6ba4d272
  2. 12 Feb, 2017 1 commit
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