linux-kernel - Re: [PATCH 2/4] ACPI: battery: Fix buffer overread if not NUL-terminated

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Message-ID: <CAJZ5v0h2vTAUovMoEoWVX2gJQiJS6C9PSYzMqQMtxPusgdHBMQ@mail.gmail.com>
Date:   Tue, 17 Jan 2023 15:42:46 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Armin Wolf <W_Armin@....de>
Cc:     rafael@...nel.org, lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] ACPI: battery: Fix buffer overread if not NUL-terminated

On Sat, Jan 14, 2023 at 9:51 AM Armin Wolf <W_Armin@....de> wrote:
>
> If the buffer containing string data is not NUL-terminated
> (which is perfectly legal according to the ACPI specification),
> the acpi battery driver might not honor its length.

Note that this is about extracting package entries of type ACPI_TYPE_BUFFER.

And please spell ACPI in capitals.

> Fix this by limiting the amount of data to be copied to
> the buffer length while also using strscpy() to make sure
> that the resulting string is always NUL-terminated.

OK

> Also use '\0' instead of a plain 0.

Why?  It's a u8, not a char.

> Signed-off-by: Armin Wolf <W_Armin@....de>
> ---
>  drivers/acpi/battery.c | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
> index fb64bd217d82..9f6daa9f2010 100644
> --- a/drivers/acpi/battery.c
> +++ b/drivers/acpi/battery.c
> @@ -438,15 +438,24 @@ static int extract_package(struct acpi_battery *battery,
>                 if (offsets[i].mode) {
>                         u8 *ptr = (u8 *)battery + offsets[i].offset;

I would add

u32 len = 32;

>
> -                       if (element->type == ACPI_TYPE_STRING ||
> -                           element->type == ACPI_TYPE_BUFFER)
> +                       switch (element->type) {

And here I would do

case ACPI_TYPE_BUFFER:
        if (len > element->buffer.length + 1)
                len = element->buffer.length + 1;

        fallthrough;
case ACPI_TYPE_STRING:
        strscpy(ptr, element->buffer.pointer, len);
        break;
case ACPI_TYPE_INTEGER:

and so on.

> +                       case ACPI_TYPE_STRING:
>                                 strscpy(ptr, element->string.pointer, 32);
> -                       else if (element->type == ACPI_TYPE_INTEGER) {
> -                               strncpy(ptr, (u8 *)&element->integer.value,
> -                                       sizeof(u64));
> +
> +                               break;
> +                       case ACPI_TYPE_BUFFER:
> +                               strscpy(ptr, element->buffer.pointer,
> +                                       min_t(u32, element->buffer.length + 1, 32));
> +
> +                               break;
> +                       case ACPI_TYPE_INTEGER:
> +                               strncpy(ptr, (u8 *)&element->integer.value, sizeof(u64));
>                                 ptr[sizeof(u64)] = 0;
> -                       } else
> -                               *ptr = 0; /* don't have value */
> +
> +                               break;
> +                       default:
> +                               *ptr = '\0'; /* don't have value */
> +                       }
>                 } else {
>                         int *x = (int *)((u8 *)battery + offsets[i].offset);
>                         *x = (element->type == ACPI_TYPE_INTEGER) ?
> --