Re: tty_mutex and tty_old_pgrp

["Jon Smirl" <jonsmirl@gmail.com>]

This selinux code is checking to see if the current process still has
access rights to it's controlling tty, right? If it doesn't tty and
tty_old_pgrp are nulled out. Does this need locking? Can you
disassociate a task like this by nulling out tty, what about the child
tasks in the session if it is the leader?

security/selinux/hooks.c

/* Derived from fs/exec.c:flush_old_files. */
static inline void flush_unauthorized_files(struct files_struct * files)
{
        struct avc_audit_data ad;
        struct file *file, *devnull = NULL;
        struct tty_struct *tty = current->signal->tty;
        struct fdtable *fdt;
        long j = -1;

        if (tty) {
                file_list_lock();
                file = list_entry(tty->tty_files.next, typeof(*file),
f_u.fu_list);
                if (file) {
                        /* Revalidate access to controlling tty.
                           Use inode_has_perm on the tty inode directly rather
                           than using file_has_perm, as this particular open
                           file may belong to another process and we are only
                           interested in the inode-based check here. */
                        struct inode *inode = file->f_dentry->d_inode;
                        if (inode_has_perm(current, inode,
                                           FILE__READ | FILE__WRITE, NULL)) {
                                /* Reset controlling tty. */
                                current->signal->tty = NULL;
                                current->signal->tty_old_pgrp = 0;
                        }
                }
                file_list_unlock();
        }



-- 
Jon Smirl
jonsmirl@gmail.com