From: Joe Perches
> Sent: 08 January 2021 00:52
...
> > The original goal was to use another helper that worked on static
> > strings like this. Linus rejected that idea, so we're in a weird place.
> > I think we could perhaps build a strcpy() replacement that requires
> > compile-time validated arguments, and to break the build if not.
> >
> > i.e.
> >
> > given:
> > char array[8];
> > char *ptr;
> >
> > allow:
> >
> >
> > strcpy(array, "1234567");
> >
> > disallow:
> >
> > strcpy(array, "12345678"); /* too long */
> > strcpy(array, src); /* not optimized, so use strscpy? */
> > strcpy(ptr, "1234567"); /* unknown destination size */
> > strcpy(ptr, src); /* unknown destination size */
>
> I think that's not a good idea as it's not a generic equivalent of the
> string.h code.
>
> I still like the stracpy variant I proposed:
>
> https://lore.kernel.org/lkml/24bb53c57767c1c2a8f266c305a67...@sk2.org/T/#m0627aa770a076af1937cb5c610ed
> 71dab3f1da72
> https://lore.kernel.org/lkml/CAHk-=wgqQKoAnhmhGE-2PBFt7oQs9LLAATKbYa573UO=dpb...@mail.gmail.com/
>
> Linus liked a variant he called copy_string:
>
> https://lore.kernel.org/lkml/CAHk-=wg8vlmmwtghxm51npswjw8rfeakoxxg0hu_q9uwbjj...@mail.gmail.com/
>
> I think the cocci scripts that convert:
>
> strlcpy -> strscpy (only when return value unused)
> str<sln>cpy(array, "string") -> stracpy(foo, "string")
> s[cn]printf -> sysfs_emit
>
> would leave relatively few uses of strcpy and sprintf variants and would
> make it much easier to analyze the remainder uses for potential overflows.
The advantage of allowing strcpy() but only when the when it can be
converted into a non-overflowing memcpy() is that you know that the
copies never get truncated.
The next round of string copy errors could easily by the 'silent truncation'
ones - so using such a strcpy() will cut down the next audit.
David
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