linux-kernel - [PATCH] Fix a use-after-free bug

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Date:   Tue, 14 Jun 2022 09:28:53 +0800
From:   Wentao_Liang <Wentao_Liang_g@....com>
To:     jdmason@...zu.us, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wentao_Liang <Wentao_Liang_g@....com>
Subject: [PATCH] Fix a use-after-free bug

The pointer vdev points to a memory region adjacent to a net_device
structure ndev, which is a field of hldev. At line 4740, the invocation
to vxge_device_unregister unregisters device hldev, and it also releases
the memory region pointed by vdev->bar0. At line 4743, the freed memory
region is referenced (i.e., iounmap(vdev->bar0)), resulting in a
use-after-free vulnerability. We can fix the bug by calling iounmap
before vxge_device_unregister.

4721.      static void vxge_remove(struct pci_dev *pdev)
4722.      {
4723.             struct __vxge_hw_device *hldev;
4724.             struct vxgedev *vdev;
…
4731.             vdev = netdev_priv(hldev->ndev);
…
4740.             vxge_device_unregister(hldev);
4741.             /* Do not call pci_disable_sriov here, as it
						will break child devices */
4742.             vxge_hw_device_terminate(hldev);
4743.             iounmap(vdev->bar0);
…
4749              vxge_debug_init(vdev->level_trace, "%s:%d
								Device unregistered",
4750                            __func__, __LINE__);
4751              vxge_debug_entryexit(vdev->level_trace, "%s:%d
								Exiting...", __func__,
4752                          __LINE__);
4753.      }

This is the screenshot when the vulnerability is triggered by using
KASAN. We can see that there is a use-after-free reported by KASAN.

/***********************report begin***************************/

root@...nel:~# echo 1 > /sys/bus/pci/devices/0000:00:03.0/remove
[  178.296316] vxge_remove
[  182.057081]
 ==================================================================
[  182.057548] BUG: KASAN: use-after-free in vxge_remove+0xe0/0x15c
[  182.057760] Read of size 8 at addr ffff888006c76598 by task bash/119
[  182.057983]
[  182.058747] CPU: 0 PID: 119 Comm: bash Not tainted 5.18.0 #5
[  182.058919] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[  182.059463] Call Trace:
[  182.059726]  <TASK>
[  182.060017]  dump_stack_lvl+0x34/0x44
[  182.060316]  print_report.cold+0xb2/0x6b7
[  182.060401]  ? kfree+0x89/0x290
[  182.060478]  ? vxge_remove+0xe0/0x15c
[  182.060545]  kasan_report+0xa9/0x120
...
[  182.070606]
 ==================================================================
[  182.071374] Disabling lock debugging due to kernel taint

/************************report end***************************/

After fixing the bug as done in the patch, we can find KASAN do not report
 the bug and the device(00:03.0) has been successfully removed.

/************************report begin*************************/

root@...nel:~# echo 1 > /sys/bus/pci/devices/0000:00:03.0/remove
root@...nel:~#

/************************report end***************************/

Signed-off-by: Wentao_Liang <Wentao_Liang_g@....com>
---
 drivers/net/ethernet/neterion/vxge/vxge-main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/neterion/vxge/vxge-main.c b/drivers/net/ethernet/neterion/vxge/vxge-main.c
index fa5d4ddf429b..092fd0ae5831 100644
--- a/drivers/net/ethernet/neterion/vxge/vxge-main.c
+++ b/drivers/net/ethernet/neterion/vxge/vxge-main.c
@@ -4736,10 +4736,10 @@ static void vxge_remove(struct pci_dev *pdev)
 	for (i = 0; i < vdev->no_of_vpath; i++)
 		vxge_free_mac_add_list(&vdev->vpaths[i]);
 
+	iounmap(vdev->bar0);
 	vxge_device_unregister(hldev);
 	/* Do not call pci_disable_sriov here, as it will break child devices */
 	vxge_hw_device_terminate(hldev);
-	iounmap(vdev->bar0);
 	pci_release_region(pdev, 0);
 	pci_disable_device(pdev);
 	driver_config->config_dev_cnt--;
-- 
2.25.1