linux-kernel - Re: [PATCH] APEI / ERST: Fix missing error handling in erst

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Date:   Fri, 15 Dec 2017 02:01:20 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Jerry Tang <jtang@...e.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] APEI / ERST: Fix missing error handling in erst_reader()

On Thu, Dec 14, 2017 at 1:31 PM, Takashi Iwai <tiwai@...e.de> wrote:
> The commit f6f828513290 ("pstore: pass allocated memory region back to
> caller") changed the check of the return value from erst_read() in
> erst_reader() in the following way:
>
>         if (len == -ENOENT)
>                 goto skip;
> -       else if (len < 0) {
> -               rc = -1;
> +       else if (len < sizeof(*rcd)) {
> +               rc = -EIO;
>                 goto out;
>
> This introduced another bug: since the comparison with sizeof() is
> cast to unsigned, a negative len value doesn't hit any longer.
> As a result, when an error is returned from erst_read(), the code
> falls through, and it may eventually lead to some weird thing like
> memory corruption.
>
> This patch adds the negative error value check more explicitly for
> addressing the issue.
>
> Fixes: f6f828513290 ("pstore: pass allocated memory region back to caller")

That's ancient. :-)

> Cc: <stable@...r.kernel.org>
> Tested-by: Jerry Tang <jtang@...e.com>
> Signed-off-by: Takashi Iwai <tiwai@...e.de>
> ---
>  drivers/acpi/apei/erst.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/apei/erst.c b/drivers/acpi/apei/erst.c
> index 6742f6c68034..9bff853e85f3 100644
> --- a/drivers/acpi/apei/erst.c
> +++ b/drivers/acpi/apei/erst.c
> @@ -1007,7 +1007,7 @@ static ssize_t erst_reader(struct pstore_record *record)
>         /* The record may be cleared by others, try read next record */
>         if (len == -ENOENT)
>                 goto skip;
> -       else if (len < sizeof(*rcd)) {
> +       else if (len < 0 || len < sizeof(*rcd)) {
>                 rc = -EIO;
>                 goto out;
>         }
> --

OK, I'm going to queue this up unless I see objections from Boris or Tony.

Thanks,
Rafael