linux-kernel - Re: [PATCH v2] test_firmware: fix end of loop test in upload_read

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Date:   Thu, 5 May 2022 11:06:51 -0700
From:   Russ Weight <russell.h.weight@...el.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Tianfei zhang <tianfei.zhang@...el.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Shawn Guo <shawn.guo@...aro.org>,
        <linux-kernel@...r.kernel.org>, <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH v2] test_firmware: fix end of loop test in
 upload_read_show()



On 5/5/22 06:10, Dan Carpenter wrote:
> If a list_for_each_entry() loop exits without hitting a break statement
> then the iterator points to invalid memory.  So in this code the
> "tst->name" dereference is an out bounds read.  It's an offset from the
> &test_upload_list pointer and it will likely work fine most of the time
> but it's not correct.
>
> One alternative is to fix this this by changing the test to:
>
> 	if (list_entry_is_head(tst, &test_upload_list, node)) {
>
> But the simpler, trendy new way is just create a new variable and test
> for NULL.
>
> Fixes: a31ad463b72d ("test_firmware: Add test support for firmware upload")
Reviewed-by: Russ Weight <russell.h.weight@...el.com>

Thanks,
- Russ

> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
>  lib/test_firmware.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
> index 76115c1a2629..c82b65947ce6 100644
> --- a/lib/test_firmware.c
> +++ b/lib/test_firmware.c
> @@ -1392,7 +1392,8 @@ static ssize_t upload_read_show(struct device *dev,
>  				struct device_attribute *attr,
>  				char *buf)
>  {
> -	struct test_firmware_upload *tst;
> +	struct test_firmware_upload *tst = NULL;
> +	struct test_firmware_upload *tst_iter;
>  	int ret = -EINVAL;
>  
>  	if (!test_fw_config->upload_name) {
> @@ -1401,11 +1402,13 @@ static ssize_t upload_read_show(struct device *dev,
>  	}
>  
>  	mutex_lock(&test_fw_mutex);
> -	list_for_each_entry(tst, &test_upload_list, node)
> -		if (tst->name == test_fw_config->upload_name)
> +	list_for_each_entry(tst_iter, &test_upload_list, node)
> +		if (tst_iter->name == test_fw_config->upload_name) {
> +			tst = tst_iter;
>  			break;
> +		}
>  
> -	if (tst->name != test_fw_config->upload_name) {
> +	if (!tst) {
>  		pr_err("Firmware name not found: %s\n",
>  		       test_fw_config->upload_name);
>  		goto out;