Re: [PATCH] vdpa/mlx5: Fix crash on shutdown for when no ndev exists

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Dragos Tatulea <dtatulea@nvidia.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Saeed Mahameed <saeedm@nvidia.com>
Subject: Re: [PATCH] vdpa/mlx5: Fix crash on shutdown for when no ndev exists
Date: Wed, 26 Jul 2023 15:26:02 -0400	[thread overview]
Message-ID: <20230726152258-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20230726190744.14143-1-dtatulea@nvidia.com>

On Wed, Jul 26, 2023 at 10:07:38PM +0300, Dragos Tatulea wrote:
> The ndev was accessed on shutdown without a check if it actually exists.
> This triggered the crash pasted below. This patch simply adds a check
> before using ndev.
> 
>  BUG: kernel NULL pointer dereference, address: 0000000000000300
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  PGD 0 P4D 0
>  Oops: 0000 [#1] SMP
>  CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 6.5.0-rc2_for_upstream_min_debug_2023_07_17_15_05 #1
>  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
>  RIP: 0010:mlx5v_shutdown+0xe/0x50 [mlx5_vdpa]
>  RSP: 0018:ffff8881003bfdc0 EFLAGS: 00010286
>  RAX: ffff888103befba0 RBX: ffff888109d28008 RCX: 0000000000000017
>  RDX: 0000000000000001 RSI: 0000000000000212 RDI: ffff888109d28000
>  RBP: 0000000000000000 R08: 0000000d3a3a3882 R09: 0000000000000001
>  R10: 0000000000000000 R11: 0000000000000000 R12: ffff888109d28000
>  R13: ffff888109d28080 R14: 00000000fee1dead R15: 0000000000000000
>  FS:  00007f4969e0be40(0000) GS:ffff88852c800000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000300 CR3: 00000001051cd006 CR4: 0000000000370eb0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  Call Trace:
>   <TASK>
>   ? __die+0x20/0x60
>   ? page_fault_oops+0x14c/0x3c0
>   ? exc_page_fault+0x75/0x140
>   ? asm_exc_page_fault+0x22/0x30
>   ? mlx5v_shutdown+0xe/0x50 [mlx5_vdpa]
>   device_shutdown+0x13e/0x1e0
>   kernel_restart+0x36/0x90
>   __do_sys_reboot+0x141/0x210
>   ? vfs_writev+0xcd/0x140
>   ? handle_mm_fault+0x161/0x260
>   ? do_writev+0x6b/0x110
>   do_syscall_64+0x3d/0x90
>   entry_SYSCALL_64_after_hwframe+0x46/0xb0
>  RIP: 0033:0x7f496990fb56
>  RSP: 002b:00007fffc7bdde88 EFLAGS: 00000206 ORIG_RAX: 00000000000000a9
>  RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f496990fb56
>  RDX: 0000000001234567 RSI: 0000000028121969 RDI: fffffffffee1dead
>  RBP: 00007fffc7bde1d0 R08: 0000000000000000 R09: 0000000000000000
>  R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
>  R13: 00007fffc7bddf10 R14: 0000000000000000 R15: 00007fffc7bde2b8
>   </TASK>
>  CR2: 0000000000000300
>  ---[ end trace 0000000000000000 ]---
> 
> Fixes: bc9a2b3e686e ("vdpa/mlx5: Support interrupt bypassing")
> Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 9138ef2fb2c8..e2e7ebd71798 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -3556,7 +3556,8 @@ static void mlx5v_shutdown(struct auxiliary_device *auxdev)
>  	mgtdev = auxiliary_get_drvdata(auxdev);
>  	ndev = mgtdev->ndev;
>  
> -	free_irqs(ndev);
> +	if (ndev)
> +		free_irqs(ndev);
>  }
>  

something I don't get:
irqs are allocated in mlx5_vdpa_dev_add
why are they not freed in mlx5_vdpa_dev_del?

this is what's creating all this mess.

>  static const struct auxiliary_device_id mlx5v_id_table[] = {
> -- 
> 2.41.0

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