linux-kernel - Re: [PATCH v8] misc: sgi-gru: fix use-after-free error in gru_set_context_option, gru_fault and gru_handle_user_call

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Date:   Wed, 9 Nov 2022 12:12:43 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zheng Wang <zyytlz.wz@....com>
Cc:     zhengyejian1@...wei.com, dimitri.sivanich@....com, arnd@...db.de,
        linux-kernel@...r.kernel.org, hackerzheng666@...il.com,
        alex000young@...il.com, security@...nel.org, sivanich@....com,
        lkp@...el.com
Subject: Re: [PATCH v8] misc: sgi-gru: fix use-after-free error in
 gru_set_context_option, gru_fault and gru_handle_user_call_os

On Wed, Nov 09, 2022 at 06:51:58PM +0800, Zheng Wang wrote:
> Gts may be freed in gru_check_chiplet_assignment.
> The caller still use it after that, UAF happens.

I do not understand what this text means, sorry.  Can you try to make it
more descriptive?

> 
> Fix it by introducing a return value to see if it's in error path or not.
> Free the gts in caller if gru_check_chiplet_assignment check failed.

Please wrap all of your changelog text at 72 columns, you have 2
paragraphs with different wrappings.

> 
> Fixes: 55484c45dbec ("gru: allow users to specify gru chiplet 2")
> Signed-off-by: Zheng Wang <zyytlz.wz@....com>
> Acked-by: Dimitri Sivanich <sivanich@....com>
> ---
> v8:
> - remove tested-by tag suggested by Greg
> 
> v7:
> - fix some spelling problems suggested by Greg, change kernel test robot from reported-by tag to tested-by tag
> 
> v6:
> - remove unused var checked by kernel test robot
> 
> v5:
> - fix logical issue and remove unnecessary variable suggested by Dimitri Sivanich
> 
> v4:
> - use VM_FAULT_NOPAGE as failure code in gru_fault and -EINVAL in other functions suggested by Yejian
> 
> v3:
> - add preempt_enable and use VM_FAULT_NOPAGE as failure code suggested by Yejian
> 
> v2:
> - commit message changes suggested by Greg
> 
> v1: https://lore.kernel.org/lkml/CAJedcCzY72jqgF-pCPtx66vXXwdPn-KMagZnqrxcpWw1NxTLaA@mail.gmail.com/
> ---
>  drivers/misc/sgi-gru/grufault.c  | 14 ++++++++++++--
>  drivers/misc/sgi-gru/grumain.c   | 16 ++++++++++++----
>  drivers/misc/sgi-gru/grutables.h |  2 +-
>  3 files changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> index d7ef61e602ed..bdd515d33225 100644
> --- a/drivers/misc/sgi-gru/grufault.c
> +++ b/drivers/misc/sgi-gru/grufault.c
> @@ -656,7 +656,9 @@ int gru_handle_user_call_os(unsigned long cb)
>  	if (ucbnum >= gts->ts_cbr_au_count * GRU_CBR_AU_SIZE)
>  		goto exit;
>  
> -	gru_check_context_placement(gts);
> +	ret = gru_check_context_placement(gts);
> +	if (ret)
> +		goto err;
>  
>  	/*
>  	 * CCH may contain stale data if ts_force_cch_reload is set.
> @@ -677,6 +679,10 @@ int gru_handle_user_call_os(unsigned long cb)
>  exit:
>  	gru_unlock_gts(gts);
>  	return ret;
> +err:
> +	gru_unlock_gts(gts);
> +	gru_unload_context(gts, 1);
> +	return -EINVAL;
>  }
>  
>  /*
> @@ -874,7 +880,11 @@ int gru_set_context_option(unsigned long arg)
>  		} else {
>  			gts->ts_user_blade_id = req.val1;
>  			gts->ts_user_chiplet_id = req.val0;
> -			gru_check_context_placement(gts);
> +			if (gru_check_context_placement(gts)) {
> +				gru_unlock_gts(gts);
> +				gru_unload_context(gts, 1);
> +				return -EINVAL;
> +			}
>  		}
>  		break;
>  	case sco_gseg_owner:
> diff --git a/drivers/misc/sgi-gru/grumain.c b/drivers/misc/sgi-gru/grumain.c
> index 9afda47efbf2..beba69fc3cd7 100644
> --- a/drivers/misc/sgi-gru/grumain.c
> +++ b/drivers/misc/sgi-gru/grumain.c
> @@ -716,9 +716,10 @@ static int gru_check_chiplet_assignment(struct gru_state *gru,
>   * chiplet. Misassignment can occur if the process migrates to a different
>   * blade or if the user changes the selected blade/chiplet.
>   */
> -void gru_check_context_placement(struct gru_thread_state *gts)
> +int gru_check_context_placement(struct gru_thread_state *gts)
>  {
>  	struct gru_state *gru;
> +	int ret = 0;
>  
>  	/*
>  	 * If the current task is the context owner, verify that the
> @@ -727,14 +728,16 @@ void gru_check_context_placement(struct gru_thread_state *gts)
>  	 */
>  	gru = gts->ts_gru;
>  	if (!gru || gts->ts_tgid_owner != current->tgid)
> -		return;
> +		return ret;

Why does this check return "all is good!" ?

Shouldn't that be an error?

thanks,

greg k-h