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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Takashi Iwai <tiwai@suse.de>
Cc: Kees Cook <keescook@chromium.org>, Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>, Tony Luck <tony.luck@intel.com>,
        Jerry Tang <jtang@suse.com>, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] APEI / ERST: Fix missing error handling in erst_reader()
Date: Sun, 17 Dec 2017 18:37:35 +0100
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On Thursday, December 14, 2017 1:31:16 PM CET Takashi Iwai 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")
> Cc: <stable@vger.kernel.org>
> Tested-by: Jerry Tang <jtang@suse.com>
> Signed-off-by: Takashi Iwai <tiwai@suse.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;
>  	}
> 

Applied, thanks!