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]> --- 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)
