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Date: Tue, 23 Jul 2019 15:41:27 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Rasmus Villemoes' <linux@...musvillemoes.dk>, Joe Perches
<joe@...ches.com>, Linus Torvalds <torvalds@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: Jonathan Corbet <corbet@....net>, Stephen Kitt <steve@....org>, Kees Cook
<keescook@...omium.org>, Nitin Gote <nitin.r.gote@...el.com>,
"jannh@...gle.com" <jannh@...gle.com>, "kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>, Andrew Morton
<akpm@...ux-foundation.org>
Subject: RE: [PATCH 1/2] string: Add stracpy and stracpy_pad mechanisms
From: Rasmus Villemoes
> Sent: 23 July 2019 07:56
...
> > +/**
> > + * stracpy - Copy a C-string into an array of char
> > + * @to: Where to copy the string, must be an array of char and not a pointer
> > + * @from: String to copy, may be a pointer or const char array
> > + *
> > + * Helper for strscpy.
> > + * Copies a maximum of sizeof(@to) bytes of @from with %NUL termination.
> > + *
> > + * Returns:
> > + * * The number of characters copied (not including the trailing %NUL)
> > + * * -E2BIG if @to is a zero size array.
>
> Well, yes, but more importantly and generally: -E2BIG if the copy
> including %NUL didn't fit. [The zero size array thing could be made into
> a build bug for these stra* variants if one thinks that might actually
> occur in real code.]
Probably better is to return the size of the destination if the copy didn't fit
(zero if the buffer is zero length).
This allows code to do repeated:
offset += str*cpy(buf + offset, src, sizeof buf - offset);
and do a final check for overflow after all the copies.
The same is true for a snprintf()like function
David
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