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

From: Ingo Molnar
Date: Mon Oct 05 2015 - 12:22:34 EST



* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> 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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