Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx> writes: > Eric W. Biederman [ebiederm@xxxxxxxxxxxx] wrote: > | > | + if (target < RESERVED_PIDS) > | > > | > Should we replace RESERVED_PIDS with 0 ? We currently allow new > | > containers to have pids 1..32K in the first pass and in subsequent > | > passes assign starting at RESERVED_PIDS. > | > | If it is a preexisting namespace pid namespace removing the RESERVED_PIDS > | check removes most if not all of the point of RESERVED_PIDS. > | > | In a new fresh pid namespace I have no problem with not performing > | the RESERVED_PIDS check. > > In that case can we do this > > if (target_pid < RESERVED_PIDS && !pid_ns->level) > return -EINVAL; > > instead ? > | > | So I guess that makes the check. > | > | if ((target < RESERVED_PIDS) && pid_ns->last_pid >= RESERVED_PIDS) > | return -EINVAL; > > I am just wondering if there is a small corner case where C/R would randomly > fail because of this sequence: > > - C/R code calls clone() or clone3() say about RESERVED_PIDS-1 > times and ->last_pid == RESERVED_PIDS-1. > > - C/R code calls normal fork()/alloc_pidmap() for a short-lived > child - its pid == ->last_pid == RESERVED_PIDS > > - C/R code then calls clone3()/set_pidmap() to set the pid of > a new child to RESERVED_PID but fails (i.e it fails to restore > a pid even when the pid is not in use). > > We could argue that mixing alloc_pidmap() and set_pidmap() during restart > is bad since set_pidmap() may fail. > > The C/R developer could argue that we are forcing them to specify a pid > even for a short lived process that they wait()s on and thus ensure that > pid is not in use. > > Anyway, is RESERVED_PIDS meant for initial kernel-threads/daemons - if so > would it be ok enforce it only in init_pid_ns ? It is mean for initial user space daemons, things that start on boot. I don't know how much the protection matters at this date, but we have it. Eric _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
