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Re: [PATCH] string: Improve the generic strlcpy() implementation

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On Mon, Oct 5, 2015 at 3:33 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> So we could solve that by adding a generic range check:
>
>  static inline int range_ok(unsigned long low, unsigned long val, unsigned long high)

So what about the type of the thing you're checking?

Maybe negative values are ok. It's unusual, but it's not unheard of.
We do have cases like

    if ((uch_config < -1) || (uch_config > 31)) {

so we have range checks that actually have signed ranges.

So I don't think a "generic" range check helper can force types like
"unsigned long".

That said, doing a simple

    git grep '<.*||.*>'

does show that the "positive or non-zero ranges with constant range
limits" case is fairly common, and maybe we could have a macro that
does some magic compile-time checking that (a) the range really is a
compile-time constant and (b) that range is valid and (c) avoids the
comparison with zero if the expression to be tested is unsigned.

So it is possible that we could enable type limit checking if we also
introduce a good way to not then create crap patches that actually
make the code more fragile or less readable. I'm not violently against
that. But I *am* violently against introducing that braindead warning
without very clear rules that we don't then have the mindless and
wrong changes to remove proper and obvious range checking and replace
it with "the expression is unsigned so we remove the nice readable
lower bounds check as unnecessary".

            Linus
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Re: [GIT PULL] strscpy string copy function Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-04 18:00 +0200
  [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 13:30 +0200
    Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 14:00 +0200
      Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 15:20 +0200
        Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 16:10 +0200
        Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 16:10 +0200
        Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 16:40 +0200
          Re: [PATCH] string: Improve the generic strlcpy() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-05 17:40 +0200
            Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 18:10 +0200
    Re: [PATCH] string: Improve the generic strlcpy() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-05 14:30 +0200
      Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 15:20 +0200
    Re: [PATCH] string: Improve the generic strlcpy() implementation Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-06 00:30 +0200
      Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-06 10:00 +0200
      Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-06 10:10 +0200
        Re: [PATCH] string: Improve the generic strlcpy() implementation Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-07 00:10 +0200
          Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-07 09:20 +0200
            Re: [PATCH] string: Improve the generic strlcpy() implementation Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-07 11:10 +0200
              Re: [PATCH] string: Improve the generic strlcpy() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-07 11:30 +0200
                Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-08 10:50 +0200
                Re: [PATCH] string: Improve the generic strlcpy() implementation Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-09 10:20 +0200
                [RFC 0/3] eliminate potential race in string() (was: [PATCH] string: Improve the generic strlcpy() implementation) Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-09 11:20 +0200
                [RFC 1/3] lib/vsprintf.c: pull out padding code from dentry_name() Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-09 11:20 +0200
                [RFC 3/3] lib/vsprintf.c: eliminate potential race in string() Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-09 11:20 +0200
                [RFC 2/3] lib/vsprintf.c: move string() below widen_string() Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-09 11:20 +0200
                Re: [RFC 0/3] eliminate potential race in string() (was: [PATCH]  string: Improve the generic strlcpy() implementation) Ingo Molnar <mingo@kernel.org> - 2015-10-10 09:50 +0200

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