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

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Date:	Mon, 5 Oct 2015 18:22:26 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] string: Improve the generic strlcpy() implementation


* Linus Torvalds <torvalds@...ux-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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