linux-kernel - Re: [PATCH] padata: use integer wrap around to prevent deadlock on seq

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Message-ID: <ims5ek6cttmbhosgo2cnv4jswwjdsfpjfzuyjmhnxy6ecdvmml@2dse43bcth6x>
Date: Tue, 13 Aug 2024 13:00:22 -0400
From: Daniel Jordan <daniel.m.jordan@...cle.com>
To: VanGiang Nguyen <vangiang.nguyen@...de-schwarz.com>
Cc: "steffen.klassert@...unet.com" <steffen.klassert@...unet.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] padata: use integer wrap around to prevent deadlock on
 seq_nr overflow

Hello Van Giang,

On Fri, Aug 09, 2024 at 06:21:42AM GMT, VanGiang Nguyen wrote:
> When submitting more than 2^32 padata objects to padata_do_serial, the
> current sorting implementation incorrectly sorts padata objects with
> overflowed seq_nr, causing them to be placed before existing objects in
> the reorder list. This leads to a deadlock in the serialization process
> as padata_find_next cannot match padata->seq_nr and pd->processed
> because the padata instance with overflowed seq_nr will be selected
> next.
> 
> To fix this, we use an unsigned integer wrap around to correctly sort
> padata objects in scenarios with integer overflow.
> 

Could use a Fixes tag like this one:

Fixes: bfde23ce200e ("padata: unbind parallel jobs from specific CPUs")

Otherwise looks good, thanks.

Acked-by: Daniel Jordan <daniel.m.jordan@...cle.com>

> Co-developed-by: Christian Gafert <christian.gafert@...de-schwarz.com>
> Signed-off-by: Christian Gafert <christian.gafert@...de-schwarz.com>
> Co-developed-by: Max Ferger <max.ferger@...de-schwarz.com>
> Signed-off-by: Max Ferger <max.ferger@...de-schwarz.com>
> Signed-off-by: Van Giang Nguyen <vangiang.nguyen@...de-schwarz.com>
> ---
>  kernel/padata.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 53f4bc912712..222bccd0c96b 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -404,7 +404,8 @@ void padata_do_serial(struct padata_priv *padata)
>  	/* Sort in ascending order of sequence number. */
>  	list_for_each_prev(pos, &reorder->list) {
>  		cur = list_entry(pos, struct padata_priv, list);
> -		if (cur->seq_nr < padata->seq_nr)
> +		/* Compare by difference to consider integer wrap around */
> +		if ((signed int)(cur->seq_nr - padata->seq_nr) < 0)
>  			break;
>  	}
>  	list_add(&padata->list, pos);
> -- 
> 2.34.1
>