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

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* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> > 2) strscpy() will copy garbage past NUL from source into destination. It won't 
> > fault but still, who knows what lies after string.
> 
> Yes, that's probably worth fixing before we get actual users..

Hm, this is the spot:

                c = *(unsigned long *)(src+res);
                *(unsigned long *)(dest+res) = c;

                if (has_zero(c, &data, &constants)) {
                        data = prep_zero_mask(c, data, &constants);
                        data = create_zero_mask(data);
                        return res + find_zero(data);
                }

We could do something like:

                c = *(unsigned long *)(src+res);
                *(unsigned long *)(dest+res) = c;

                if (has_zero(c, &data, &constants)) {
			unsigned int zero_pos;

                        data = prep_zero_mask(c, data, &constants);
                        data = create_zero_mask(data);

			zero_pos = find_zero(data);
			res += zero_pos;

			memset(dest+res, 0, sizeof(long)-zero_pos);

                        return res;
                }

I.e. the extra memset() clears out the partial word (if any) after the NUL.

Completely untested.

Thanks,

	Ingo
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Re: [PATCH] string: Improve the generic strlcpy() implementation Alexey Dobriyan <adobriyan@gmail.com> - 2015-10-05 17:40 +0200
  Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 18:20 +0200
    Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 18:20 +0200
  Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 18:30 +0200
    [PATCH] string: Fix strscpy() uninitialized data copy bug Ingo Molnar <mingo@kernel.org> - 2015-10-05 18:40 +0200
      Re: [PATCH] string: Fix strscpy() uninitialized data copy bug Chris Metcalf <cmetcalf@ezchip.com> - 2015-10-05 21:00 +0200
        Re: [PATCH] string: Fix strscpy() uninitialized data copy bug Ingo Molnar <mingo@kernel.org> - 2015-10-06 09:30 +0200
  Re: [PATCH] string: Improve the generic strlcpy() implementation Ingo Molnar <mingo@kernel.org> - 2015-10-05 18:30 +0200
    Re: [PATCH] string: Improve the generic strlcpy() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-05 22:50 +0200
      Re: [PATCH] strscpy: zero any trailing garbage bytes in the  destination Ingo Molnar <mingo@kernel.org> - 2015-10-07 09:30 +0200

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