Messages in this thread | | | Date | Tue, 24 Aug 2021 20:26:10 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v4] EDAC/mc: Prefer strscpy over strcpy |
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On Tue, Aug 24, 2021 at 12:28:07PM +0200, Len Baker wrote: > This is a task of the KSPP [1] and the main reason is to clean up the > proliferation of str*cpy functions in the kernel.
That I understood - you prominently explain where the patches stem from.
What I can't parse is that formulation "previous step". What previous step do you mean?
> Yes, you are right. The same discussion happened in the v3 review [2] and > I agree with the reasons that Robert Richter exposed. Using the strlen() > implementation it is not necessary to check the return code of strcpy and > we can assume a silent truncation. > > [2] https://lore.kernel.org/linux-hardening/YRN+8u59lJ6MWsOL@rric.localdomain/
Ok, looking at the asm, gcc is actually smart enough not to call strlen() twice on the same buffer.
But then there's this in the strscpy() kernel-doc comment:
"The destination buffer is always NUL terminated, unless it's zero-sized."
so looking at the code, we're merrily decrementing len but nothing's checking whether len can become 0. Because if it does, strscpy() will do:
if (count == 0 || WARN_ON_ONCE(count > INT_MAX)) return -E2BIG;
so if p ends up pointing to something which is *not* '\0', strlen() will go off into the weeds.
So I don't care if it doesn't look just as nice - it better be correct in all cases first.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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