access_ok problem through system_call

[Andi Kleen]

niloufer en utdallas.edu (Niloufer Vajifdar) writes:

> hi,
> 
> i'm new to linux kernel programming and i'm having the following problem:
> 
> When trying to use the sys_read and sys_write calls from within another
> system call the return value is -14 (bad address EFAULT). This seems to be
> happening because the 'access_ok' function is not allowing the access to
> the buffer being used to read or write. 
> 
> Could someone explain why this is happening? Is it wrong to use
> sys_read/sys_write through another system call?

You have to do 

mm_segment_t oldfs = get_fs(); set_fs(KERNEL_DS); 
/* call system call with kernel pointers */ 
set_fs(oldfs): 

Otherwise it would be possible for every user to access kernel memory
by passing pointers to it to system calls.

-Andi

-- 
This is like TV. I don't like TV.

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