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SubjectRe: Coccinelle: Checking of_node_put() calls with SmPL
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On 07/10/2019 11:35 PM, wen.yang99@zte.com.cn wrote:
>>> we developed a coccinelle script to detect such problems.
>>
>> Would you find the implementation of the function “dt_init_idle_driver”
>> suspicious according to discussed source code search patterns?
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/cpuidle/dt_idle_states.c?id=e9a83bd2322035ed9d7dcf35753d3f984d76c6a5#n208
>> https://elixir.bootlin.com/linux/v5.2/source/drivers/cpuidle/dt_idle_states.c#L208
>>
>>
>>> This script is still being improved.
>>
>> Will corresponding software development challenges become more interesting?
>
> Hello Markus,
> This is the simplified code pattern for it:
>
> 172 for (i = 0; ; i++) {

This loop can only be exited on a break.

> 173 state_node = of_parse_phandle(...); ---> Obtain here
> ...
> 177 match_id = of_match_node(matches, state_node);
> 178 if (!match_id) {
> 179 err = -ENODEV;
> 180 break; ---> Jump out of the loop without releasing it
> 181 }
> 182
> 183 if (!of_device_is_available(state_node)) {
> 184 of_node_put(state_node);
> 185 continue; ---> Release the object references within a loop
> 186 }
> ...
> 208 of_node_put(state_node); --> Release the object references within a loop

This is required at the end of every loop or continue to free the reference.
Only a break will exit the loop where we hit the below of_node_put().

> 209 }
> 210
> 211 of_node_put(state_node); --> There may be double free here.

None of the break conditions call of_node_put(), so it needs to be called here.

-Tyrel

>
> This code pattern is very interesting and the coccinelle software should also recognize this pattern.
>
> Regards,
> Wen
>

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