linux-kernel - Re: [PATCH net] ice: fix invalid check for empty list in ice_sched_assoc_vsi_to

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Date:   Tue, 14 Mar 2023 11:50:58 -0700
From:   Tony Nguyen <anthony.l.nguyen@...el.com>
To:     Jakob Koschel <jkl820.git@...il.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
CC:     <intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Pietro Borrello <borrello@...g.uniroma1.it>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH net] ice: fix invalid check for empty list in
 ice_sched_assoc_vsi_to_agg()

On 3/13/2023 9:31 AM, Jakob Koschel wrote:
> The code implicitly assumes that the list iterator finds a correct
> handle. If 'vsi_handle' is not found the 'old_agg_vsi_info' was
> pointing to an bogus memory location. For safety a separate list
> iterator variable should be used to make the != NULL check on
> 'old_agg_vsi_info' correct under any circumstances.
> 
> Additionally Linus proposed to avoid any use of the list iterator
> variable after the loop, in the attempt to move the list iterator
> variable declaration into the macro to avoid any potential misuse after
> the loop. Using it in a pointer comparision after the loop is undefined
> behavior and should be omitted if possible [1].
> 
> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
> Signed-off-by: Jakob Koschel <jkl820.git@...il.com>

The patch looks fine, however, for net patches, could you please include 
a Fixes: tag.

Thanks,
Tony

> ---
>   drivers/net/ethernet/intel/ice/ice_sched.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_sched.c b/drivers/net/ethernet/intel/ice/ice_sched.c
> index 4eca8d195ef0..b7682de0ae05 100644
> --- a/drivers/net/ethernet/intel/ice/ice_sched.c
> +++ b/drivers/net/ethernet/intel/ice/ice_sched.c
> @@ -2788,7 +2788,7 @@ static int
>   ice_sched_assoc_vsi_to_agg(struct ice_port_info *pi, u32 agg_id,
>   			   u16 vsi_handle, unsigned long *tc_bitmap)
>   {
> -	struct ice_sched_agg_vsi_info *agg_vsi_info, *old_agg_vsi_info = NULL;
> +	struct ice_sched_agg_vsi_info *agg_vsi_info, *iter, *old_agg_vsi_info = NULL;
>   	struct ice_sched_agg_info *agg_info, *old_agg_info;
>   	struct ice_hw *hw = pi->hw;
>   	int status = 0;
> @@ -2806,11 +2806,13 @@ ice_sched_assoc_vsi_to_agg(struct ice_port_info *pi, u32 agg_id,
>   	if (old_agg_info && old_agg_info != agg_info) {
>   		struct ice_sched_agg_vsi_info *vtmp;
>   
> -		list_for_each_entry_safe(old_agg_vsi_info, vtmp,
> +		list_for_each_entry_safe(iter, vtmp,
>   					 &old_agg_info->agg_vsi_list,
>   					 list_entry)
> -			if (old_agg_vsi_info->vsi_handle == vsi_handle)
> +			if (iter->vsi_handle == vsi_handle) {
> +				old_agg_vsi_info = iter;
>   				break;
> +			}
>   	}
>   
>   	/* check if entry already exist */
> 
> ---
> base-commit: eeac8ede17557680855031c6f305ece2378af326
> change-id: 20230301-ice-fix-invalid-iterator-found-check-0a3e5b43dfb3
> 
> Best regards,