linux-kernel - Re: [PATCH] ACPI: extlog fix null dereference check

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Date:   Mon, 4 Dec 2023 13:01:48 -0500
From:   Prarit Bhargava <prarit@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
        David Arcari <darcari@...hat.com>,
        Don Zickus <dzickus@...hat.com>,
        David Malcolm <dmalcolm@...hat.com>
Subject: Re: [PATCH] ACPI: extlog fix null dereference check

Top posting and just adding a few interested parties ...

On 12/4/23 13:00, Prarit Bhargava wrote:
> The gcc plugin -fanalyzer [1] tries to detect various
> patterns of incorrect behaviour.  The tool reports
> 
> drivers/acpi/acpi_extlog.c: In function ‘extlog_exit’:
> drivers/acpi/acpi_extlog.c:307:12: warning: check of ‘extlog_l1_addr’ for NULL after already dereferencing it [-Wanalyzer-deref-before-check]
>      |
>      |  306 |         ((struct extlog_l1_head *)extlog_l1_addr)->flags &= ~FLAG_OS_OPTIN;
>      |      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
>      |      |                                                  |
>      |      |                                                  (1) pointer ‘extlog_l1_addr’ is dereferenced here
>      |  307 |         if (extlog_l1_addr)
>      |      |            ~
>      |      |            |
>      |      |            (2) pointer ‘extlog_l1_addr’ is checked for NULL here but it was already dereferenced at (1)
>      |
> 
> Fix the null dereference check in extlog_exit().
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Static-Analyzer-Options.html
> 
> CC: "Rafael J. Wysocki" <rafael@...nel.org>
> CC: Len Brown <lenb@...nel.org>
> CC: linux-acpi@...r.kernel.org
> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> ---
>   drivers/acpi/acpi_extlog.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_extlog.c b/drivers/acpi/acpi_extlog.c
> index e120a96e1eae..193147769146 100644
> --- a/drivers/acpi/acpi_extlog.c
> +++ b/drivers/acpi/acpi_extlog.c
> @@ -303,9 +303,10 @@ static int __init extlog_init(void)
>   static void __exit extlog_exit(void)
>   {
>   	mce_unregister_decode_chain(&extlog_mce_dec);
> -	((struct extlog_l1_head *)extlog_l1_addr)->flags &= ~FLAG_OS_OPTIN;
> -	if (extlog_l1_addr)
> +	if (extlog_l1_addr) {
> +		((struct extlog_l1_head *)extlog_l1_addr)->flags &= ~FLAG_OS_OPTIN;
>   		acpi_os_unmap_iomem(extlog_l1_addr, l1_size);
> +	}
>   	if (elog_addr)
>   		acpi_os_unmap_iomem(elog_addr, elog_size);
>   	release_mem_region(elog_base, elog_size);