On July 24, 2019 8:14:26 PM GMT+02:00, Jann Horn <jannh@xxxxxxxxxx> wrote: >On Wed, Jul 24, 2019 at 4:48 PM Christian Brauner ><christian@xxxxxxxxxx> wrote: >> If CLONE_WAIT_PID is set the newly created process will not be >> considered by process wait requests that wait generically on children >> such as: >> >> syscall(__NR_wait4, -1, wstatus, options, rusage) >> syscall(__NR_waitpid, -1, wstatus, options) >> syscall(__NR_waitid, P_ALL, -1, siginfo, options, rusage) >> syscall(__NR_waitid, P_PGID, -1, siginfo, options, rusage) >> syscall(__NR_waitpid, -pid, wstatus, options) >> syscall(__NR_wait4, -pid, wstatus, options, rusage) >> >> A process created with CLONE_WAIT_PID can only be waited upon with a >> focussed wait call. This ensures that processes can be reaped even if >> all file descriptors referring to it are closed. >[...] >> diff --git a/kernel/fork.c b/kernel/fork.c >> index baaff6570517..a067f3876e2e 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -1910,6 +1910,8 @@ static __latent_entropy struct task_struct >*copy_process( >> delayacct_tsk_init(p); /* Must remain after >dup_task_struct() */ >> p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE); >> p->flags |= PF_FORKNOEXEC; >> + if (clone_flags & CLONE_WAIT_PID) >> + p->flags |= PF_WAIT_PID; >> INIT_LIST_HEAD(&p->children); >> INIT_LIST_HEAD(&p->sibling); >> rcu_copy_process(p); > >This means that if a process with PF_WAIT_PID forks, the child >inherits the flag, right? That seems unintended? You might have to add >something like "if (clone_flags & CLONE_THREAD == 0) p->flags &= >~PF_WAIT_PID;" before this. (I think threads do have to inherit the >flag so that the case where a non-leader thread of the child goes >through execve and steals the leader's identity is handled properly.) >Or you could cram it somewhere into signal_struct instead of on the >task - that might be a more logical place for it? Hm, CLONE_WAIT_PID is only useable with CLONE_PIDFD which in turn is not useable with CLONE_THREAD. But we should probably make that explicit for CLONE_WAIT_PID too.
