Hi folks,
I'd like to build some authentication daemon which alters the

privileges of another process (like factotum does on plan9).

But I couldn't find any interface for that (setuid() and friends

only operate on the current process). So I'm now going to create

my own interface.
As a little learning example I just added a few files to the

per-pid dirs: uid, euid, suid, fsuid. This was trivial :)
Now I'd like to add an write capability to these files:

simply writing another number changes the (|s|fs)uid.
But this doesnt seem that trivial. Perhaps someone could give

me some advice ?
cu

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 Enrico Weigelt    ==   metux IT service - http://www.metux.de/

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Not really hard, is it? Just look at something like oom_adj
static ssize_t myprocpid_euid_write(struct file *file,

    const char __user *inbuf, size_t size)

{

	struct task_struct *task;

	char buf[sizeof("4294967296")];

	unsigned int amount = min(size, sizeof(buf) - 1);
	if (copy_from_user(buf, inbuf, amount) != 0)

		return -EFAULT;

	buf[amount] = '\0';
	task = get_proc_task(file->f_path.dentry->d_inode);

	if (task == NULL)

		return -ESRCH;
	/* do error checking */

	task->euid = simple_strtoul(buf, NULL, 0);

	put_task_struct(task);

	return size;

}
So far the theory..

--

Well, it's not that trivial than just an ro string file.

But not that hard as I first suspected :)
I've introduced a few new helpers for rw integers, which works

quite similar to the ro string stuff, but with anouther handler type.
I'll post a patch in the new testers list.
The next step is actually changing the uid. Can I just write

new values to the uid field(s) in the task struct or is there

something tricky about that ?
cu

--

---------------------------------------------------------------------

 Enrico Weigelt    ==   metux IT service - http://www.metux.de/

---------------------------------------------------------------------

 Please visit the OpenSource QM Taskforce:

 	http://wiki.metux.de/public/OpenSource_QM_Taskforce

 Patches / Fixes for a lot dozens of packages in dozens of versions:

	http://patches.metux.de/

---------------------------------------------------------------------

--