Quoting Kirill Tkhai ([email protected]): > On implementing of nested pid namespaces support in CRIU > (checkpoint-restore in userspace tool) we run into > the situation, that it's impossible to create a task with > specific NSpid effectively. After commit 49f4d8b93ccf > "pidns: Capture the user namespace and filter ns_last_pid" > it is impossible to set ns_last_pid on any pid namespace, > except task's active pid_ns (before the commit it was possible > to write to pid_ns_for_children). Thus, if a restored task > in a container has more than one pid_ns levels, the restorer > code must have a task helper for every pid namespace > of the task's pid_ns hierarhy. > > This is a big problem, because of communication with > a helper for every pid_ns in the hierarchy is not cheap > and not performance-good as it implies many helpers wakeups > to create a single task (independently, how you communicate > with the helpers). This patch tries to decide the problem. > > It introduces a new pid_ns ns_ioctl(PIDNS_REQ_SET_LAST_PID_VEC), > which allows to write a vector of last pids on pid_ns hierarchy. > The vector is passed as a ":"-delimited string with pids, > written in reverse order. The first number corresponds to > the opened namespace ns_last_pid, the second is to its parent, etc. > So, if you have the pid namespaces hierarchy like: > > pid_ns1 (grand father) > | > v > pid_ns2 (father) > | > v > pid_ns3 (child) > > and the ns of task's of pid_ns3 is open, then the corresponding > vector will be "last_ns_pid3:last_ns_pid2:last_ns_pid1". This > vector may be short and it may contain less levels, for example, > "last_ns_pid3:last_ns_pid2" or even "last_ns_pid3", in dependence > of which levels you want to populate. > > To write in a pid_ns's ns_last_pid we check that the writer task > has CAP_SYS_ADMIN permittions in this pid_ns's user_ns. > > One note about struct pidns_ioc_req. It's made extensible and > may expanded in the future. The always existing fields present > at the moment, the future fields and they sizes may be determined > by pidns_ioc_req::req by the future code. > > Signed-off-by: Kirill Tkhai <[email protected]>
Reviewed-by: Serge Hallyn <[email protected]> (for both patches) > --- > include/uapi/linux/nsfs.h | 9 +++++ > kernel/pid_namespace.c | 88 > +++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 97 insertions(+) > > diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h > index 544bbb661475..37bb4af917b5 100644 > --- a/include/uapi/linux/nsfs.h > +++ b/include/uapi/linux/nsfs.h > @@ -17,4 +17,13 @@ > /* Execute namespace-specific ioctl */ > #define NS_SPECIFIC_IOC _IO(NSIO, 0x5) > > +struct pidns_ioc_req { > +/* Set vector of last pids in namespace hierarchy */ > +#define PIDNS_REQ_SET_LAST_PID_VEC 0x1 > + unsigned int req; > + void __user *data; > + unsigned int data_size; > + char std_fields[0]; > +}; > + > #endif /* __LINUX_NSFS_H */ > diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c > index de461aa0bf9a..0e86fa15cd92 100644 > --- a/kernel/pid_namespace.c > +++ b/kernel/pid_namespace.c > @@ -21,6 +21,8 @@ > #include <linux/export.h> > #include <linux/sched/task.h> > #include <linux/sched/signal.h> > +#include <linux/vmalloc.h> > +#include <uapi/linux/nsfs.h> > > struct pid_cache { > int nr_ids; > @@ -428,6 +430,91 @@ static struct ns_common *pidns_get_parent(struct > ns_common *ns) > return &get_pid_ns(pid_ns)->ns; > } > > +#ifdef CONFIG_CHECKPOINT_RESTORE > +static long set_last_pid_vec(struct pid_namespace *pid_ns, > + struct pidns_ioc_req *req) > +{ > + char *str, *p; > + int ret = 0; > + pid_t pid; > + > + read_lock(&tasklist_lock); > + if (!pid_ns->child_reaper) > + ret = -EINVAL; > + read_unlock(&tasklist_lock); > + if (ret) > + return ret; > + > + if (req->data_size >= PAGE_SIZE) > + return -EINVAL; > + str = vmalloc(req->data_size + 1); > + if (!str) > + return -ENOMEM; > + if (copy_from_user(str, req->data, req->data_size)) { > + ret = -EFAULT; > + goto out_vfree; > + } > + str[req->data_size] = '\0'; > + > + p = str; > + while (p && *p != '\0') { > + if (!ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN)) { > + ret = -EPERM; > + goto out_vfree; > + } > + > + if (sscanf(p, "%d", &pid) != 1 || pid < 0 || pid > pid_max) { > + ret = -EINVAL; > + goto out_vfree; > + } > + > + /* Write directly: see the comment in pid_ns_ctl_handler() */ > + pid_ns->last_pid = pid; > + > + p = strchr(p, ':'); > + pid_ns = pid_ns->parent; > + if (p) { > + if (!pid_ns) { > + ret = -EINVAL; > + goto out_vfree; > + } > + p++; > + } > + } > + > + ret = 0; > +out_vfree: > + vfree(str); > + return ret; > +} > +#else /* CONFIG_CHECKPOINT_RESTORE */ > +static long set_last_pid_vec(struct pid_namespace *pid_ns, > + struct pidns_ioc_req *req) > +{ > + return -ENOTTY; > +} > +#endif /* CONFIG_CHECKPOINT_RESTORE */ > + > +static long pidns_ioctl(struct ns_common *ns, unsigned long arg) > +{ > + struct pid_namespace *pid_ns = to_pid_ns(ns); > + struct pidns_ioc_req user_req; > + int ret; > + > + ret = copy_from_user(&user_req, (void *)arg, > + offsetof(struct pidns_ioc_req, std_fields)); > + if (ret) > + return ret; > + > + switch (user_req.req) { > + case PIDNS_REQ_SET_LAST_PID_VEC: > + return set_last_pid_vec(pid_ns, &user_req); > + default: > + return -ENOTTY; > + } > + return 0; > +} > + > static struct user_namespace *pidns_owner(struct ns_common *ns) > { > return to_pid_ns(ns)->user_ns; > @@ -441,6 +528,7 @@ const struct proc_ns_operations pidns_operations = { > .install = pidns_install, > .owner = pidns_owner, > .get_parent = pidns_get_parent, > + .ns_ioctl = pidns_ioctl, > }; > > static __init int pid_namespaces_init(void)
