Re: [PATCH] sysctl: Check length at deprecated_sysctl_warning.

[ebiederm@xmission.com (Eric W. Biederman)]

Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> writes:

> Hello.
>
> Andrew Morton wrote:
>> I believe (args->nlen > CTL_MAXNAME) was correct.
> I'll leave it to you.
> But if you want to allow args->nlen == CTL_MAXNAME,
> you also need to update do_sysctl().

Which has been that way since before I decided to touch it. 2.6.12-rc1.
I haven't tracked it before then as I don't expect to see anything.

And that is why -ENOTDIR.  That is the historical error code from sysctl in
this case.

> int do_sysctl(int __user *name, int nlen, void __user *oldval, size_t __user
> *oldlenp,
>                void __user *newval, size_t newlen)
> {
>         ...
>         if (nlen <= 0 || nlen >= CTL_MAXNAME)
>                 return -ENOTDIR;
>         ...
> }

CTL_MAXNAME is fairly arbitrary, and since the set of binary paths is fixed.
So it feels to me like the code really should read:

        if (nlen <= 0 || nlen > CTL_MAXNAME)
                return -ENOTDIR;

In both places. Just because that is what the comment describes.

I think in reality CTL_MAXNAME is actually 5 but I would have to look a little
more closely to confirm that.

Eric