linux-kernel - Re: [PATCH] kho: make sure kho_scratch argument is fully consumed

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Message-ID: <aK6b1_UI-xw2rtlZ@kernel.org>
Date: Wed, 27 Aug 2025 08:47:03 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Alexander Graf <graf@...zon.com>, Changyuan Lyu <changyuanl@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, kexec@...ts.infradead.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kho: make sure kho_scratch argument is fully consumed

On Tue, Aug 26, 2025 at 02:38:16PM +0200, Pratyush Yadav wrote:
> When specifying fixed sized scratch areas, the parser only parses the
> three scratch sizes and ignores the rest of the argument. This means the
> argument can have any bogus trailing characters.
> 
> For example, "kho_scratch=256M,512M,512Mfoobar" results in successful
> parsing:
> 
>     [    0.000000] KHO: scratch areas: lowmem: 256MiB global: 512MiB pernode: 512MiB
> 
> It is generally a good idea to parse arguments as strictly as possible.
> In addition, if bogus trailing characters are allowed in the kho_scratch
> argument, it is possible that some people might end up using them and
> later extensions to the argument format will cause unexpected breakages.
> 
> Make sure the argument is fully consumed after all three scratch sizes
> are parsed. With this change, the bogus argument
> "kho_scratch=256M,512M,512Mfoobar" results in:
> 
>     [    0.000000] Malformed early option 'kho_scratch'
> 
> Signed-off-by: Pratyush Yadav <pratyush@...nel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
>  kernel/kexec_handover.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index ecd1ac210dbd7..a90d55121a7a0 100644
> --- a/kernel/kexec_handover.c
> +++ b/kernel/kexec_handover.c
> @@ -446,6 +446,10 @@ static int __init kho_parse_scratch_size(char *p)
>  		p = endp;
>  	}
>  
> +	/* The string should be fully consumed by now. */
> +	if (*p)
> +		return -EINVAL;
> +
>  	scratch_size_lowmem = sizes[0];
>  	scratch_size_global = sizes[1];
>  	scratch_size_pernode = sizes[2];
> -- 
> 2.47.3
> 

-- 
Sincerely yours,
Mike.