Re: [PATH 0/2] strndup_user, description

[Davi Arnaut <davi.arnaut@gmail.com>]

On Wed, 15 Feb 2006 02:53:10 +0000
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> On Maw, 2006-02-14 at 21:47 -0300, Davi Arnaut wrote:
> > This patch series creates a strndup_user() function in order to avoid duplicated
> > and error-prone (userspace modifying the string after the strlen_user()) code.
> 
> Well userspace can still modify in this case. So you could still get a
> \0 mid buffer but that seems harmless.

Yes.

> However
> 
> > +#define strdup_user(s)	strndup_user(s, PAGE_SIZE)
> 
> Better this doesn't exist as it is a wrapper for a bad habit that isnt
> yet used so why encourage it.
> 

Ok, I will inline it.
 
> 
> > +	length = strlen_user(s);
> 
> What if n is very large ? Should use strnlen_user clipped by n

That's what "if (length > n) length = n" is for.
 
> Also say the length limit is 8 and the text is "hello\0"
> 
> We get length = 5  5 < 8, alloc 5 bytes set 5th to \0 and return "hell
> \0"

No, we would get length = 6, strlen_user returns the size of the string
_including_ the terminating NUL.

--
Davi Arnaut

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