Re: filldir[64] oddness

[Vadim Lobanov <vlobanov@speakeasy.net>]

On Wed, 8 Mar 2006, Dave Jones wrote:

> I'm puzzled by an aparent use of uninitialised memory
> that coverity's checker picked up.
>
> fs/readdir.c
>
> #define NAME_OFFSET(de) ((int) ((de)->d_name - (char __user *) (de)))
> #define ROUND_UP(x) (((x)+sizeof(long)-1) & ~(sizeof(long)-1))
>
> 140  	static int filldir(void * __buf, const char * name, int namlen, loff_t offset,
> 141  			   ino_t ino, unsigned int d_type)
> 142  	{
> 143  		struct linux_dirent __user * dirent;
> 144  		struct getdents_callback * buf = (struct getdents_callback *) __buf
> 145  		int reclen = ROUND_UP(NAME_OFFSET(dirent) + namlen + 2);
>
> How come that NAME_OFFSET isn't causing an oops when
> it dereferences stackjunk->d_name ?

If I had to guess...

Because NAME_OFFSET(de) is essentially doing
	de->d_name - de
which should be equivalent to just the static offset of d_name within
struct linux_direct. Which should be constant, no? Why does it need to
pass a pointer to compute this? Who knows.

> 		Dave
>
> --
> http://www.codemonkey.org.uk

- Vadim Lobanov