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

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Message-ID: <YnPFh6ULhhPloue2@bombadil.infradead.org>
Date:   Thu, 5 May 2022 05:39:35 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Russ Weight <russell.h.weight@...el.com>,
        Tianfei zhang <tianfei.zhang@...el.com>,
        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] test_firmware: fix end of loop test in upload_read_show()

On Thu, May 05, 2022 at 01:29:15PM +0300, Dan Carpenter wrote:
> If we iterate through a loop using list_for_each_entry() without
> hitting a break, then the iterator points to bogus memory.  The
> if (tst->name != test_fw_config->upload_name) { will likely still work
> but technically it's an out of bounds read.
> 
> Fixes: a31ad463b72d ("test_firmware: Add test support for firmware upload")
> 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);

Note the mutex lock.

> -	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 a lock is held I can't see how the premise of this patch is
correct and we ensure we don't remove entries while holdingg
the lock.

Generalizing this problem seems like a bigger issue, no?

Additionally this patch doesn't apply at all on linux-next.

  Luis

> +		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;
> -- 
> 2.35.1
>