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SubjectRe: [PATCH 1/2] sysctl: add overflow detection to proc_get_long()
On Sun, Oct 14, 2018 at 06:18:55PM +0100, Al Viro wrote:
> On Sun, Oct 14, 2018 at 03:25:09PM +0200, Christian Brauner wrote:
>
> > +static unsigned long sysctl_strtoul_lenient(const char *cp, char **endp,
> > + unsigned int base, bool *overflow)
> > +{
> > + unsigned long long result;
> > + unsigned int rv;
> > +
> > + cp = _parse_integer_fixup_radix(cp, &base);
> > + rv = _parse_integer(cp, base, &result);
> > + if ((rv & KSTRTOX_OVERFLOW) ||
> > + (result != (unsigned long long)(unsigned long)result))
> > + *overflow = true;
> > + else
> > + *overflow = false;
>
> Yecchh... First of all, the cast back to unsigned long long is completely
> pointless. What's more,

Sorry, seriously asking: why? This was meant to handle the case where
sizeof(unsigned long long) != sizeof(unsigned long) and I just looked at
_kstrtoul() which does the same:

int _kstrtoul(const char *s, unsigned int base, unsigned long *res)
{
unsigned long long tmp;
int rv;

rv = kstrtoull(s, base, &tmp);
if (rv < 0)
return rv;
if (tmp != (unsigned long long)(unsigned long)tmp)
return -ERANGE;
*res = tmp;
return 0;
}

Sorry, if I'm being dense here.

> if (expr)
> foo = true;
> else
> foo = flase;
> is a fairly unidiomatic way to spell foo = expr;
>
> And... is there anything that would really care if this "overflow" thing had
> been replaced by simply returning ~0UL on such? That would appear to be
> a lot more natural API...

Yes, I thought about this but I really didn't want to risk breaking
anything that relies on the weird old behavior. We can change it to that
and assume that anything that doesn't explicitly set a maximum value
wants to be capped at ULONG_MAX. Fine with me.

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