fober@grame.fr (Dominique Fober) writes:
> Some of the kernel exported symbols allows to acces files (open.c : filp_open, filp_close). However, the 'generic_file_read' function (filemap.c) seems to be restricted to buffers located in user space (access_ok macro)
> (which prevents it from being called by a kernel module).
> I would like to know the reason of this restriction which seems to be arbitrary as
> bypassing the check don't affect the function behavior.
Oh it does. Then you be able to read random kernel addresses from
every file system using generic_file_read, stealing other users data.
Now when you want to read a file from kernel space you usually have
a bug in the design. In Unix this should be near always be done by user space
not in the kernel (e.g. to load firmware you would write a small utility
that loads them into your driver using a special ioctl etc.). Usually
you do not want to deal with path names in kernel drivers, that's
bad style.
That being said, you can prevent the access_ok() check by using
mm_segment_t oldfs = get_fs();
set_fs(KERNEL_DS);
/* call */
set_fs(oldfs);
-Andi
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This archive was generated by hypermail 2b29 : Mon Feb 07 2000 - 21:00:06 EST