tty: Properly fix memleak of alloc_pid

Cylen Yao <cylen.yao@mediatek.com>
bug: 7845126 MT67x2

Memleak is due to unreleased pid->count, which execute in function:
get_pid()(pid->count++) and put_pid()(pid->count--).

The race condition as following:
task[dumpsys]               task[adbd]
in disassociate_ctty()      in tty_signal_session_leader()
-----------------------     -------------------------
tty = get_current_tty();
// tty is not NULL
...
spin_lock_irq(&current->sighand->siglock);
put_pid(current->signal->tty_old_pgrp);
current->signal->tty_old_pgrp = NULL;
spin_unlock_irq(&current->sighand->siglock);

                            spin_lock_irq(&p->sighand->siglock);
                            ...
                            p->signal->tty = NULL;
                            ...
                            spin_unlock_irq(&p->sighand->siglock);

tty = get_current_tty();
// tty NULL, goto else branch by accident.
if (tty) {
    ...
    put_pid(tty_session);
    put_pid(tty_pgrp);
    ...
} else {
    print msg
}

in task[dumpsys], in disassociate_ctty(), tty is set NULL by task[adbd],
tty_signal_session_leader(), then it goto else branch and lack of
put_pid(), cause memleak.

move spin_unlock(sighand->siglock) after get_current_tty() can avoid
the race and fix the memleak.

0 files changed, 0 insertions, 0 deletions