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

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] string: Improve the generic strlcpy() implementation
Date	2015-10-05 14:00 +0200
Message-ID	<qgcAW-6rH-11@gated-at.bofh.it> (permalink)
References	<q7g13-2Rm-7@gated-at.bofh.it> <qfTRD-4Np-7@gated-at.bofh.it> <qgc7U-5TG-9@gated-at.bofh.it>
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* Ingo Molnar <mingo@kernel.org> wrote:

> 2)
> 
> Another problem is that strlcpy() will also happily do bad stuff if we pass
> it a negative size. Instead of that we will from now on print a (one time)
> warning and return safely.

Hm, so this check is buggy, as 'size_t' is unsigned - and for some reason GCC 
didn't warn about the never-met comparison and the resulting unreachable dead
code here:

> +	/* Overflow check: */
> +	if (unlikely(dest_size < 0)) {
> +		WARN_ONCE(1, "strlcpy(): dest_size < 0 underflow!");
> +		return strlen(src);
> +	}

which is annoying.

Would people object to something like:

> +	/* Overflow check: */
> +	if (unlikely((ssize_t)dest_size < 0)) {
> +		WARN_ONCE(1, "strlcpy(): dest_size < 0 underflow!");
> +		return strlen(src);
> +	}

?

As I doubt it's legit to have larger than 2GB strings.

Also, I'm wondering why GCC didn't warn.

Thanks,

	Ingo
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Thread

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

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