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 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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