linux-kernel - Re: [PATCH v2] tty: vt: keyboard: initialize "kbs" so that kfree(kbs) runs fine even if kbs is not kmalloced.

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Message-ID: <CAHP4M8XaWtagZcocGoeT2Rb6F6JeKqMFa2ZzTZ0ddCES0-T-jw@mail.gmail.com>
Date:   Sat, 6 Nov 2021 17:46:45 +0530
From:   Ajay Garg <ajaygargnsit@...il.com>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tty: vt: keyboard: initialize "kbs" so that kfree(kbs)
 runs fine even if kbs is not kmalloced.

Hi Pavel,

Thanks for the review.

>
> Please, don't put change log into commit message. It should go under ---
>

Ok, many thanks Pavel.
Will take care in all my future patches.

>
> These is only one caller of vt_do_kdgkb_ioctl, which simple does:
>
>
>         case KDGKBSENT:
>         case KDSKBSENT:
>                 return vt_do_kdgkb_ioctl(cmd, up, perm);
>
> It means, that cmd can not be different from KDGKBSENT and KDSKBSENT.
>
> I guess, you found this "issue" via static analysis tool like smatch or
> smth similar, but this bug is impossible right now.
>

Yes, following was reported by smatch (amongst others) :
vt_do_kdgkb_ioctl() error: uninitialized symbol 'kbs'.

Regarding the current state, "vt_do_kdgkb_ioctl" should ideally behave
correctly independently, without bothering whether a cmd is a valid
one. From that perspective, it makes sense to ensure that kfree never
crashes.

However, I don't have any strong opinions on what is right or what is
wrong, as long as things work fine.

So, if there is a general consensus that the change should not be made
currently, I would be ok.
In case the change should be made, kindly let me know, I will post the
v3 patch (making change as per the review-comment of moving changelog
below ---).

Thanks and Regards,
Ajay