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From:   Duoming Zhou <duoming@zju.edu.cn>
To:     linux-kernel@vger.kernel.org, kuba@kernel.org,
        krzysztof.kozlowski@linaro.org, gregkh@linuxfoundation.org
Cc:     davem@davemloft.net, edumazet@google.com, pabeni@redhat.com,
        alexander.deucher@amd.com, akpm@linux-foundation.org,
        broonie@kernel.org, netdev@vger.kernel.org, linma@zju.edu.cn,
        Duoming Zhou <duoming@zju.edu.cn>
Subject: [PATCH net v5 2/2] nfc: nfcmrvl: main: reorder destructive operations in nfcmrvl_nci_unregister_dev to avoid bugs
Date:   Fri, 29 Apr 2022 09:14:33 +0800
Message-Id: <bb2769acc79f42d25d61ed8988c8d240c8585f33.1651194245.git.duoming@zju.edu.cn>
In-Reply-To: <cover.1651194245.git.duoming@zju.edu.cn>
References: <cover.1651194245.git.duoming@zju.edu.cn>
In-Reply-To: <cover.1651194245.git.duoming@zju.edu.cn>
References: <cover.1651194245.git.duoming@zju.edu.cn>
Precedence: bulk

There are destructive operations such as nfcmrvl_fw_dnld_abort and
gpio_free in nfcmrvl_nci_unregister_dev. The resources such as firmware,
gpio and so on could be destructed while the upper layer functions such as
nfcmrvl_fw_dnld_start and nfcmrvl_nci_recv_frame is executing, which leads
to double-free, use-after-free and null-ptr-deref bugs.

There are three situations that could lead to double-free bugs.

The first situation is shown below:

   (Thread 1)                 |      (Thread 2)
nfcmrvl_fw_dnld_start         |
 ...                          |  nfcmrvl_nci_unregister_dev
 release_firmware()           |   nfcmrvl_fw_dnld_abort
  kfree(fw) //(1)             |    fw_dnld_over
                              |     release_firmware
  ...                         |      kfree(fw) //(2)
                              |     ...

The second situation is shown below:

   (Thread 1)                 |      (Thread 2)
nfcmrvl_fw_dnld_start         |
 ...                          |
 mod_timer                    |
 (wait a time)                |
 fw_dnld_timeout              |  nfcmrvl_nci_unregister_dev
   fw_dnld_over               |   nfcmrvl_fw_dnld_abort
    release_firmware          |    fw_dnld_over
     kfree(fw) //(1)          |     release_firmware
     ...                      |      kfree(fw) //(2)

The third situation is shown below:

       (Thread 1)               |       (Thread 2)
nfcmrvl_nci_recv_frame          |
 if(..->fw_download_in_progress)|
  nfcmrvl_fw_dnld_recv_frame    |
   queue_work                   |
                                |
fw_dnld_rx_work                 | nfcmrvl_nci_unregister_dev
 fw_dnld_over                   |  nfcmrvl_fw_dnld_abort
  release_firmware              |   fw_dnld_over
   kfree(fw) //(1)              |    release_firmware
                                |     kfree(fw) //(2)

The firmware struct is deallocated in position (1) and deallocated
in position (2) again.

The crash trace triggered by POC is like below:

[  122.640457] BUG: KASAN: double-free or invalid-free in fw_dnld_over+0x28/0xf0
[  122.640457] Call Trace:
[  122.640457]  <TASK>
[  122.640457]  kfree+0xb0/0x330
[  122.640457]  fw_dnld_over+0x28/0xf0
[  122.640457]  nfcmrvl_nci_unregister_dev+0x61/0x70
[  122.640457]  nci_uart_tty_close+0x87/0xd0
[  122.640457]  tty_ldisc_kill+0x3e/0x80
[  122.640457]  tty_ldisc_hangup+0x1b2/0x2c0
[  122.640457]  __tty_hangup.part.0+0x316/0x520
[  122.640457]  tty_release+0x200/0x670
[  122.640457]  __fput+0x110/0x410
[  122.640457]  task_work_run+0x86/0xd0
[  122.640457]  exit_to_user_mode_prepare+0x1aa/0x1b0
[  122.640457]  syscall_exit_to_user_mode+0x19/0x50
[  122.640457]  do_syscall_64+0x48/0x90
[  122.640457]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[  122.640457] RIP: 0033:0x7f68433f6beb

What's more, there are also use-after-free and null-ptr-deref bugs
in nfcmrvl_fw_dnld_start. If we deallocate firmware struct, gpio or
set null to the members of priv->fw_dnld in nfcmrvl_nci_unregister_dev,
then, we dereference firmware, gpio or the members of priv->fw_dnld in
nfcmrvl_fw_dnld_start, the UAF or NPD bugs will happen.

This patch reorders destructive operations after nci_unregister_device
and uses bool variable in nfc_dev to synchronize between cleanup routine
and firmware download routine. The process is shown below.

       (Thread 1)                 |       (Thread 2)
nfcmrvl_nci_unregister_dev        |
  nci_unregister_device           |
    nfc_unregister_device         | nfc_fw_download
      device_lock()               |
      ...                         |
      dev->dev_register = false;  |   ...
      device_unlock()             |
  ...                             |   device_lock()
  (destructive operations)        |   if(!dev->dev_register)
                                  |     goto error;
                                  | error:
                                  |   device_unlock()

If the device is detaching, the download function will goto error.
If the download function is executing, nci_unregister_device will
wait until download function is finished.

Fixes: 3194c6870158 ("NFC: nfcmrvl: add firmware download support")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
Changes in v5:
  - Use bool variable added in patch 1/2 to synchronize.

 drivers/nfc/nfcmrvl/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nfc/nfcmrvl/main.c b/drivers/nfc/nfcmrvl/main.c
index 2fcf545012b..1a5284de434 100644
--- a/drivers/nfc/nfcmrvl/main.c
+++ b/drivers/nfc/nfcmrvl/main.c
@@ -183,6 +183,7 @@ void nfcmrvl_nci_unregister_dev(struct nfcmrvl_private *priv)
 {
 	struct nci_dev *ndev = priv->ndev;
 
+	nci_unregister_device(ndev);
 	if (priv->ndev->nfc_dev->fw_download_in_progress)
 		nfcmrvl_fw_dnld_abort(priv);
 
@@ -191,7 +192,6 @@ void nfcmrvl_nci_unregister_dev(struct nfcmrvl_private *priv)
 	if (gpio_is_valid(priv->config.reset_n_io))
 		gpio_free(priv->config.reset_n_io);
 
-	nci_unregister_device(ndev);
 	nci_free_device(ndev);
 	kfree(priv);
 }
-- 
2.17.1