linux-kernel - Re: [PATCH v2 next] ACPI: APEI: EINJ: prevent memory corruption in error_type

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Message-ID: <ks34mfmv2vhwojpxlzv7tyordcjdo6zclcflplvs2wsl6gkbn5@3v5kguelmita>
Date: Wed, 25 Jun 2025 20:04:14 +0200
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Zaid Alali <zaidal@...amperecomputing.com>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, James Morse <james.morse@....com>, 
	Tony Luck <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>, Ira Weiny <ira.weiny@...el.com>, 
	Jonathan Cameron <Jonathan.Cameron@...wei.com>, Dan Williams <dan.j.williams@...el.com>, 
	Al Viro <viro@...iv.linux.org.uk>, Sudeep Holla <sudeep.holla@....com>, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2 next] ACPI: APEI: EINJ: prevent memory corruption in
 error_type_set()

Hello Dan,

On Wed, Jun 25, 2025 at 11:34:38AM -0500, Dan Carpenter wrote:
> The "einj_buf" buffer is 32 chars.  Verify that "count" is not too large
> for that.  Also leave the last character as a NUL terminator to ensure
> the string is properly terminated.
> 
> Fixes: 0c6176e1e186 ("ACPI: APEI: EINJ: Enable the discovery of EINJv2 capabilities")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
> v2: I messed up the sizeof() calculation in the copy_from_user() and I put
>     the parentheses in the wrong place in v1.
> 
>  drivers/acpi/apei/einj-core.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/apei/einj-core.c b/drivers/acpi/apei/einj-core.c
> index d6d7e36e3647..2206cbbdccfa 100644
> --- a/drivers/acpi/apei/einj-core.c
> +++ b/drivers/acpi/apei/einj-core.c
> @@ -826,8 +826,11 @@ static ssize_t error_type_set(struct file *file, const char __user *buf,
>  	int rc;
>  	u64 val;
>  
> +	if (count > sizeof(einj_buf))
> +		return -EINVAL;
> +
>  	memset(einj_buf, 0, sizeof(einj_buf));
> -	if (copy_from_user(einj_buf, buf, count))

I would add a comment here to explain the -1. It's in the commit log,
but that doesn't help a future reader.

> +	if (copy_from_user(einj_buf, buf, min(count, sizeof(einj_buf) - 1)))
>  		return -EFAULT;
>  
>  	if (strncmp(einj_buf, "V2_", 3) == 0) {

Further down there is:

	return count;

Is that still correct given that you read less now?

Best regards
Uwe

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