Re: [TOMOYO #5 02/18] Add wrapper functions for VFShelperfunctions.

Tetsuo Handa
2007-11-17T05:24:17Z

Hello.

Trond Myklebust wrote:
> I'm confused. How do you tell the difference between a 'userland'
> request and a 'kernel' request, and why is the latter safe from a
> security perspective?
For example, if userland process wants to create a directory,
it will call mkdir(2).
In the kernel, mkdir(2) is mapped to sys_mkdir(),
sys_mkdir() calls sys_mkdirat(),
sys_mkdirat() calls vfs_mkdir().

Therefore, there is a chance to tell whether
vfs_mkdir() is triggered by userland process's request.
Some kernel code *might* call sys_mkdir() too.
But at least I think I can hook all requests
triggered by userland process's request
because routes to call vfs_mkdir() from userland is not infinite.

We are regarding the kernel code as trusted.
For example, no security checks for code that are called by only kernel.
http://www.mail-archive.com/linux-security-module@vger.kernel.org/msg01830.html

Regards.