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SubjectRe: API for changing UIDs of other processes

On Friday 2008-05-02 14:16, Enrico Weigelt wrote:
>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 ?

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..


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