linux-kernel - Re: [PATCH] selftests/resctrl: Fix null pointer dereference on open failed

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Message-ID: <04a35a47-d83a-67a1-5ed4-ba314c6e1ecf@linuxfoundation.org>
Date:   Mon, 25 Apr 2022 09:51:16 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Colin Ian King <colin.i.king@...il.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Shuah Khan <shuah@...nel.org>, Babu Moger <babu.moger@....com>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        linux-kselftest@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] selftests/resctrl: Fix null pointer dereference on open
 failed

On 4/24/22 3:15 PM, Colin Ian King wrote:
> Currently if opening /dev/null fails to open then file pointer fp
> is null and further access to fp via fprintf will cause a null
> pointer dereference. Fix this by returning a negative error value
> when a null fp is detected.
> 

How did you find this problem and how can it be reproduced? Is there
a case where test fails to open "/dev/null"?

> Fixes: a2561b12fe39 ("selftests/resctrl: Add built in benchmark")
> Signed-off-by: Colin Ian King <colin.i.king@...il.com>
> ---
>   tools/testing/selftests/resctrl/fill_buf.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c
> index 51e5cf22632f..56ccbeae0638 100644
> --- a/tools/testing/selftests/resctrl/fill_buf.c
> +++ b/tools/testing/selftests/resctrl/fill_buf.c
> @@ -121,8 +121,10 @@ static int fill_cache_read(unsigned char *start_ptr, unsigned char *end_ptr,
>   
>   	/* Consume read result so that reading memory is not optimized out. */
>   	fp = fopen("/dev/null", "w");
> -	if (!fp)
> +	if (!fp) {
>   		perror("Unable to write to /dev/null");
> +		return -1;
> +	}
>   	fprintf(fp, "Sum: %d ", ret);
>   	fclose(fp);
>   
> 

thanks,
-- Shuah