linux-kernel - Re: [PATCH] ksmbd: remove unnecessary conditions

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Date:   Tue, 7 Sep 2021 13:17:05 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Namjae Jeon <linkinjeon@...nel.org>,
        Steve French <sfrench@...ba.org>,
        Hyunchul Lee <hyc.lee@...il.com>, linux-cifs@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ksmbd: remove unnecessary conditions

On Tue, Sep 07, 2021 at 06:59:38PM +0900, Sergey Senozhatsky wrote:
> On (21/09/07 12:14), Dan Carpenter wrote:
> [..]
> > > > > 
> > > > > Can make_kuid() return INVALID_UID? IOW, uid_valid(uid) here as well?
> > > > 
> > > > No need to check twice.  We're going to check at the end.
> > > > 
> > > > > 
> > > > > > +
> > > > > > +		/* If this is an idmapped mount, apply the idmapping. */
> > > > > > +		uid = kuid_from_mnt(user_ns, uid);
> > > > > > +		if (uid_valid(uid)) {
> > > >                     ^^^^^^^^^^^^^^
> > > > The check here is sufficient.
> > > 
> > > My point was more that a potentially invalid UID is passed to kuid_from_mnt()
> > > and kgid_from_mnt(). I don't see map_id_up(), for example, checking that
> > > passed UID is valid. So decided to double check.
> > 
> > But you've seen it now, right?
> 
> A linear search in array of 5 elements or a binary search in array of 340
> elements? Yea, I saw it. I'd prefer one extra uid_valid(), if you'd ask
> me - why call the function if we already know that it'll fail.

It's a failure path.  Hopefully people will only give us valid data.

We would normally only optimize the failure path if we thought that it
could be used as a DoS vector.

regards,
dan carpenter