On 26/03/2021 15.22, Peter Zijlstra wrote:
> On Fri, Mar 26, 2021 at 01:53:59PM +0100, Rasmus Villemoes wrote:
>> On 26/03/2021 12.38, Peter Zijlstra wrote:
>
>>> +
>>> +again:
>>> + rcu_read_lock();
>>> + str = rcu_dereference(*(char **)file->private_data);
>>> + len = strlen(str) + 1;
>>> +
>>> + if (!copy || copy_len < len) {
>>> + rcu_read_unlock();
>>> + kfree(copy);
>>> + copy = kmalloc(len + 1, GFP_KERNEL);
>>> + if (!copy) {
>>> + debugfs_file_put(dentry);
>>> + return -ENOMEM;
>>> + }
>>> + copy_len = len;
>>> + goto again;
>>> + }
>>> +
>>> + strncpy(copy, str, len);
>>> + copy[len] = '\n';
>>> + copy[len+1] = '\0';
>>> + rcu_read_unlock();
>>
>> As noted (accidentally off-list), this is broken. I think you want this
>> on top
>>
>> - len = strlen(str) + 1;
>> + len = strlen(str);
>
> kmalloc(len + 2, ...);
No, because nul-terminating the stuff you pass to
simple_read_from_buffer is pointless cargo-culting. Yeah, read_file_bool
does it, but that's just bogus.
>> - strncpy(copy, str, len);
>> + memcpy(copy, str, len);
>> copy[len] = '\n';
>> - copy[len+1] = '\0';
>
> I'll go with strscpy() I tihnk, something like:
>
> len = strscpy(copy, str, len);
> if (len < 0)
> return len;
To what end? The only way that could possibly return -EFOO is if the
nul-terminator in str vanished between the strlen() and here, and in
that case you have bigger problems.
> copy[len] = '\n';
> copy[len + 1] = '\0';
>
>>> +EXPORT_SYMBOL_GPL(debugfs_read_file_str);
>>
>> Why?
>
> Copy-pasta from debugfs_*_bool(). This thing seems to export everything
> and I figured I'd go along with that.
I thought the convention was not to export anything until the kernel
itself had a (modular) user. But I can't find that stated under
Documentation/ anywhere - but it does say "Every function that is
exported to loadable modules using
``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` should have a kernel-doc
comment.". Anyway, the *_bool stuff doesn't seem to be something to be
copy-pasted.
Rasmus
