On 2024/12/10 04:34, Rob Herring wrote:
> On Thu, Dec 5, 2024 at 6:53 PM Zijun Hu <zijun_hu@xxxxxxxxxx> wrote:
>>
>> From: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
>>
>> of_device_uevent_modalias() saves MODALIAS value from offset
>> (@env->buflen - 1), so the available buffer size should be
>> (sizeof(@env->buf) - @env->buflen + 1), but it uses the wrong
>> size (sizeof(@env->buf) - @env->buflen).
>>
>> Fix by using right size (sizeof(@env->buf) - @env->buflen + 1).
>
> Just writing what the diff says already is not that useful. The key
> part you need to know is why we back up by 1 character to begin with.
>
will correct commit message in v2.
>>
>> Fixes: dd27dcda37f0 ("of/device: merge of_device_uevent")
>> Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
>> ---
>> drivers/of/device.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/of/device.c b/drivers/of/device.c
>> index edf3be1972658f6dc165f577da53b10c7eebc116..ee29c07c83b9e6abd9b1c7747dd341026bc79eb0 100644
>> --- a/drivers/of/device.c
>> +++ b/drivers/of/device.c
>> @@ -266,10 +266,10 @@ int of_device_uevent_modalias(const struct device *dev, struct kobj_uevent_env *
>> return -ENOMEM;
>>
>> sl = of_modalias(dev->of_node, &env->buf[env->buflen-1],
>
> This could use a comment why we back up by 1. Better to put it in a
> variable than add/subtract 1 everywhere:
>
> /* After add_uevent_event(), buflen is at character after the nul char
> which needs to be overwritten */
> buflen = env->buflen - 1;
>
> And then use 'buflen' throughout.
>
good proposal. may use it for v2 after discussion done.
>> - sizeof(env->buf) - env->buflen);
>> + sizeof(env->buf) - env->buflen + 1);
>> if (sl < 0)
>> return sl;
>> - if (sl >= (sizeof(env->buf) - env->buflen))
>> + if (sl >= (sizeof(env->buf) - env->buflen + 1))
>> return -ENOMEM;
>
> There's another potential problem. If we return before here, we end up
> with "OF_MODALIAS=\0" or "OF_MODALIAS=some-non-nul-terminated-str".
> Maybe that doesn't matter? I haven't looked at the caller.
>
that does not matter since current logic follows below 2 rules
1) all strings in @env->buf always terminated with '\0'.
2) both env->buflen and env->envp_idx are not updated once @env->buf
does not enough spaces then failed.
current logic has no difference with normal add_uevent_var() usage.
> I think a better solution to all this would be making add_uevent_var
> work to construct the full value. We could add "%pOFm" format that
> calls of_mod_alias(). Then this function becomes just:
>
of_modalias() ?
agree with you.
for good practice, users should only use uevent APIs and should not
depend on uevent's internal implementation.
> return add_uevent_var(env, "MODALIAS=%pOFm");
>
> And of_device_modalias() can be:
>
> sl = snprintf(str, len, "%pOFm\n", dev->of_node);
> if (sl >= len)
> return -ENOMEM;
> return sl;
>
looks good.
of_request_module() provides another solution.
> Rob
