From 7863dcc72d0f4b13a641065670426435448b3d80 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 22 Nov 2024 14:24:58 +0100 Subject: [PATCH 1/2] pid: allow pid_max to be set per pid namespace The pid_max sysctl is a global value. For a long time the default value has been 65535 and during the pidfd dicussions Linus proposed to bump pid_max by default (cf. [1]). Based on this discussion systemd started bumping pid_max to 2^22. So all new systems now run with a very high pid_max limit with some distros having also backported that change. The decision to bump pid_max is obviously correct. It just doesn't make a lot of sense nowadays to enforce such a low pid number. There's sufficient tooling to make selecting specific processes without typing really large pid numbers available. In any case, there are workloads that have expections about how large pid numbers they accept. Either for historical reasons or architectural reasons. One concreate example is the 32-bit version of Android's bionic libc which requires pid numbers less than 65536. There are workloads where it is run in a 32-bit container on a 64-bit kernel. If the host has a pid_max value greater than 65535 the libc will abort thread creation because of size assumptions of pthread_mutex_t. That's a fairly specific use-case however, in general specific workloads that are moved into containers running on a host with a new kernel and a new systemd can run into issues with large pid_max values. Obviously making assumptions about the size of the allocated pid is suboptimal but we have userspace that does it. Of course, giving containers the ability to restrict the number of processes in their respective pid namespace indepent of the global limit through pid_max is something desirable in itself and comes in handy in general. Independent of motivating use-cases the existence of pid namespaces makes this also a good semantical extension and there have been prior proposals pushing in a similar direction. The trick here is to minimize the risk of regressions which I think is doable. The fact that pid namespaces are hierarchical will help us here. What we mostly care about is that when the host sets a low pid_max limit, say (crazy number) 100 that no descendant pid namespace can allocate a higher pid number in its namespace. Since pid allocation is hierarchial this can be ensured by checking each pid allocation against the pid namespace's pid_max limit. This means if the allocation in the descendant pid namespace succeeds, the ancestor pid namespace can reject it. If the ancestor pid namespace has a higher limit than the descendant pid namespace the descendant pid namespace will reject the pid allocation. The ancestor pid namespace will obviously not care about this. All in all this means pid_max continues to enforce a system wide limit on the number of processes but allows pid namespaces sufficient leeway in handling workloads with assumptions about pid values and allows containers to restrict the number of processes in a pid namespace through the pid_max interface. [1]: https://lore.kernel.org/linux-api/CAHk-=wiZ40LVjnXSi9iHLE_-ZBsWFGCgdmNiYZUXn1-V5YBg2g@mail.gmail.com - rebased from 5.14-rc1 - a few fixes (missing ns_free_inum on error path, missing initialization, etc) - permission check changes in pid_table_root_permissions - unsigned int pid_max -> int pid_max (keep pid_max type as it was) - add READ_ONCE in alloc_pid() as suggested by Christian - rebased from 6.7 and take into account: * sysctl: treewide: drop unused argument ctl_table_root::set_ownership(table) * sysctl: treewide: constify ctl_table_header::ctl_table_arg * pidfd: add pidfs * tracing: Move saved_cmdline code into trace_sched_switch.c Signed-off-by: Alexander Mikhalitsyn Link: https://lore.kernel.org/r/20241122132459.135120-2-aleksandr.mikhalitsyn@canonical.com Signed-off-by: Christian Brauner --- include/linux/pid.h | 3 - include/linux/pid_namespace.h | 10 ++- kernel/pid.c | 125 ++++++++++++++++++++++++++++-- kernel/pid_namespace.c | 43 +++++++--- kernel/sysctl.c | 9 --- kernel/trace/pid_list.c | 2 +- kernel/trace/trace.h | 2 - kernel/trace/trace_sched_switch.c | 2 +- 8 files changed, 161 insertions(+), 35 deletions(-) diff --git a/include/linux/pid.h b/include/linux/pid.h index a3aad9b4074c..c800cbee584b 100644 --- a/include/linux/pid.h +++ b/include/linux/pid.h @@ -106,9 +106,6 @@ extern void exchange_tids(struct task_struct *task, struct task_struct *old); extern void transfer_pid(struct task_struct *old, struct task_struct *new, enum pid_type); -extern int pid_max; -extern int pid_max_min, pid_max_max; - /* * look up a PID in the hash table. Must be called with the tasklist_lock * or rcu_read_lock() held. diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h index f9f9931e02d6..7c67a5811199 100644 --- a/include/linux/pid_namespace.h +++ b/include/linux/pid_namespace.h @@ -30,6 +30,7 @@ struct pid_namespace { struct task_struct *child_reaper; struct kmem_cache *pid_cachep; unsigned int level; + int pid_max; struct pid_namespace *parent; #ifdef CONFIG_BSD_PROCESS_ACCT struct fs_pin *bacct; @@ -38,9 +39,14 @@ struct pid_namespace { struct ucounts *ucounts; int reboot; /* group exit code if this pidns was rebooted */ struct ns_common ns; -#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE) + struct work_struct work; +#ifdef CONFIG_SYSCTL + struct ctl_table_set set; + struct ctl_table_header *sysctls; +#if defined(CONFIG_MEMFD_CREATE) int memfd_noexec_scope; #endif +#endif } __randomize_layout; extern struct pid_namespace init_pid_ns; @@ -117,6 +123,8 @@ static inline int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd) extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk); void pidhash_init(void); void pid_idr_init(void); +int register_pidns_sysctls(struct pid_namespace *pidns); +void unregister_pidns_sysctls(struct pid_namespace *pidns); static inline bool task_is_in_init_pid_ns(struct task_struct *tsk) { diff --git a/kernel/pid.c b/kernel/pid.c index 115448e89c3e..ce3e94e26a0f 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -60,10 +60,8 @@ struct pid init_struct_pid = { }, } }; -int pid_max = PID_MAX_DEFAULT; - -int pid_max_min = RESERVED_PIDS + 1; -int pid_max_max = PID_MAX_LIMIT; +static int pid_max_min = RESERVED_PIDS + 1; +static int pid_max_max = PID_MAX_LIMIT; /* * Pseudo filesystems start inode numbering after one. We use Reserved * PIDs as a natural offset. @@ -87,6 +85,7 @@ struct pid_namespace init_pid_ns = { #ifdef CONFIG_PID_NS .ns.ops = &pidns_operations, #endif + .pid_max = PID_MAX_DEFAULT, #if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE) .memfd_noexec_scope = MEMFD_NOEXEC_SCOPE_EXEC, #endif @@ -193,6 +192,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, for (i = ns->level; i >= 0; i--) { int tid = 0; + int pid_max = READ_ONCE(tmp->pid_max); if (set_tid_size) { tid = set_tid[ns->level - i]; @@ -644,17 +644,118 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags) return fd; } +#ifdef CONFIG_SYSCTL +static struct ctl_table_set *pid_table_root_lookup(struct ctl_table_root *root) +{ + return &task_active_pid_ns(current)->set; +} + +static int set_is_seen(struct ctl_table_set *set) +{ + return &task_active_pid_ns(current)->set == set; +} + +static int pid_table_root_permissions(struct ctl_table_header *head, + const struct ctl_table *table) +{ + struct pid_namespace *pidns = + container_of(head->set, struct pid_namespace, set); + int mode = table->mode; + + if (ns_capable(pidns->user_ns, CAP_SYS_ADMIN) || + uid_eq(current_euid(), make_kuid(pidns->user_ns, 0))) + mode = (mode & S_IRWXU) >> 6; + else if (in_egroup_p(make_kgid(pidns->user_ns, 0))) + mode = (mode & S_IRWXG) >> 3; + else + mode = mode & S_IROTH; + return (mode << 6) | (mode << 3) | mode; +} + +static void pid_table_root_set_ownership(struct ctl_table_header *head, + kuid_t *uid, kgid_t *gid) +{ + struct pid_namespace *pidns = + container_of(head->set, struct pid_namespace, set); + kuid_t ns_root_uid; + kgid_t ns_root_gid; + + ns_root_uid = make_kuid(pidns->user_ns, 0); + if (uid_valid(ns_root_uid)) + *uid = ns_root_uid; + + ns_root_gid = make_kgid(pidns->user_ns, 0); + if (gid_valid(ns_root_gid)) + *gid = ns_root_gid; +} + +static struct ctl_table_root pid_table_root = { + .lookup = pid_table_root_lookup, + .permissions = pid_table_root_permissions, + .set_ownership = pid_table_root_set_ownership, +}; + +static struct ctl_table pid_table[] = { + { + .procname = "pid_max", + .data = &init_pid_ns.pid_max, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &pid_max_min, + .extra2 = &pid_max_max, + }, +}; +#endif + +int register_pidns_sysctls(struct pid_namespace *pidns) +{ +#ifdef CONFIG_SYSCTL + struct ctl_table *tbl; + + setup_sysctl_set(&pidns->set, &pid_table_root, set_is_seen); + + tbl = kmemdup(pid_table, sizeof(pid_table), GFP_KERNEL); + if (!tbl) + return -ENOMEM; + tbl->data = &pidns->pid_max; + pidns->pid_max = min(pid_max_max, max_t(int, pidns->pid_max, + PIDS_PER_CPU_DEFAULT * num_possible_cpus())); + + pidns->sysctls = __register_sysctl_table(&pidns->set, "kernel", tbl, + ARRAY_SIZE(pid_table)); + if (!pidns->sysctls) { + kfree(tbl); + retire_sysctl_set(&pidns->set); + return -ENOMEM; + } +#endif + return 0; +} + +void unregister_pidns_sysctls(struct pid_namespace *pidns) +{ +#ifdef CONFIG_SYSCTL + const struct ctl_table *tbl; + + tbl = pidns->sysctls->ctl_table_arg; + unregister_sysctl_table(pidns->sysctls); + retire_sysctl_set(&pidns->set); + kfree(tbl); +#endif +} + void __init pid_idr_init(void) { /* Verify no one has done anything silly: */ BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING); /* bump default and minimum pid_max based on number of cpus */ - pid_max = min(pid_max_max, max_t(int, pid_max, - PIDS_PER_CPU_DEFAULT * num_possible_cpus())); + init_pid_ns.pid_max = min(pid_max_max, max_t(int, init_pid_ns.pid_max, + PIDS_PER_CPU_DEFAULT * num_possible_cpus())); pid_max_min = max_t(int, pid_max_min, PIDS_PER_CPU_MIN * num_possible_cpus()); - pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min); + pr_info("pid_max: default: %u minimum: %u\n", init_pid_ns.pid_max, pid_max_min); idr_init(&init_pid_ns.idr); @@ -665,6 +766,16 @@ void __init pid_idr_init(void) NULL); } +static __init int pid_namespace_sysctl_init(void) +{ +#ifdef CONFIG_SYSCTL + /* "kernel" directory will have already been initialized. */ + BUG_ON(register_pidns_sysctls(&init_pid_ns)); +#endif + return 0; +} +subsys_initcall(pid_namespace_sysctl_init); + static struct file *__pidfd_fget(struct task_struct *task, int fd) { struct file *file; diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index d70ab49d5b4a..f1ffa032fc32 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -70,6 +70,8 @@ static void dec_pid_namespaces(struct ucounts *ucounts) dec_ucount(ucounts, UCOUNT_PID_NAMESPACES); } +static void destroy_pid_namespace_work(struct work_struct *work); + static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns, struct pid_namespace *parent_pid_ns) { @@ -105,17 +107,27 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns goto out_free_idr; ns->ns.ops = &pidns_operations; + ns->pid_max = parent_pid_ns->pid_max; + err = register_pidns_sysctls(ns); + if (err) + goto out_free_inum; + refcount_set(&ns->ns.count, 1); ns->level = level; ns->parent = get_pid_ns(parent_pid_ns); ns->user_ns = get_user_ns(user_ns); ns->ucounts = ucounts; ns->pid_allocated = PIDNS_ADDING; + INIT_WORK(&ns->work, destroy_pid_namespace_work); + #if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE) ns->memfd_noexec_scope = pidns_memfd_noexec_scope(parent_pid_ns); #endif + return ns; +out_free_inum: + ns_free_inum(&ns->ns); out_free_idr: idr_destroy(&ns->idr); kmem_cache_free(pid_ns_cachep, ns); @@ -137,12 +149,28 @@ static void delayed_free_pidns(struct rcu_head *p) static void destroy_pid_namespace(struct pid_namespace *ns) { + unregister_pidns_sysctls(ns); + ns_free_inum(&ns->ns); idr_destroy(&ns->idr); call_rcu(&ns->rcu, delayed_free_pidns); } +static void destroy_pid_namespace_work(struct work_struct *work) +{ + struct pid_namespace *ns = + container_of(work, struct pid_namespace, work); + + do { + struct pid_namespace *parent; + + parent = ns->parent; + destroy_pid_namespace(ns); + ns = parent; + } while (ns != &init_pid_ns && refcount_dec_and_test(&ns->ns.count)); +} + struct pid_namespace *copy_pid_ns(unsigned long flags, struct user_namespace *user_ns, struct pid_namespace *old_ns) { @@ -155,15 +183,8 @@ struct pid_namespace *copy_pid_ns(unsigned long flags, void put_pid_ns(struct pid_namespace *ns) { - struct pid_namespace *parent; - - while (ns != &init_pid_ns) { - parent = ns->parent; - if (!refcount_dec_and_test(&ns->ns.count)) - break; - destroy_pid_namespace(ns); - ns = parent; - } + if (ns && ns != &init_pid_ns && refcount_dec_and_test(&ns->ns.count)) + schedule_work(&ns->work); } EXPORT_SYMBOL_GPL(put_pid_ns); @@ -274,6 +295,7 @@ static int pid_ns_ctl_handler(const struct ctl_table *table, int write, next = idr_get_cursor(&pid_ns->idr) - 1; tmp.data = &next; + tmp.extra2 = &pid_ns->pid_max; ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos); if (!ret && write) idr_set_cursor(&pid_ns->idr, next + 1); @@ -281,7 +303,6 @@ static int pid_ns_ctl_handler(const struct ctl_table *table, int write, return ret; } -extern int pid_max; static struct ctl_table pid_ns_ctl_table[] = { { .procname = "ns_last_pid", @@ -289,7 +310,7 @@ static struct ctl_table pid_ns_ctl_table[] = { .mode = 0666, /* permissions are checked in the handler */ .proc_handler = pid_ns_ctl_handler, .extra1 = SYSCTL_ZERO, - .extra2 = &pid_max, + .extra2 = &init_pid_ns.pid_max, }, }; #endif /* CONFIG_CHECKPOINT_RESTORE */ diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 5c9202cb8f59..7ae7a4136855 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1803,15 +1803,6 @@ static struct ctl_table kern_table[] = { .proc_handler = proc_dointvec, }, #endif - { - .procname = "pid_max", - .data = &pid_max, - .maxlen = sizeof (int), - .mode = 0644, - .proc_handler = proc_dointvec_minmax, - .extra1 = &pid_max_min, - .extra2 = &pid_max_max, - }, { .procname = "panic_on_oops", .data = &panic_on_oops, diff --git a/kernel/trace/pid_list.c b/kernel/trace/pid_list.c index 4966e6bbdf6f..c62b9b3cfb3d 100644 --- a/kernel/trace/pid_list.c +++ b/kernel/trace/pid_list.c @@ -414,7 +414,7 @@ struct trace_pid_list *trace_pid_list_alloc(void) int i; /* According to linux/thread.h, pids can be no bigger that 30 bits */ - WARN_ON_ONCE(pid_max > (1 << 30)); + WARN_ON_ONCE(init_pid_ns.pid_max > (1 << 30)); pid_list = kzalloc(sizeof(*pid_list), GFP_KERNEL); if (!pid_list) diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 266740b4e121..91def760f364 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -718,8 +718,6 @@ extern unsigned long tracing_thresh; /* PID filtering */ -extern int pid_max; - bool trace_find_filtered_pid(struct trace_pid_list *filtered_pids, pid_t search_pid); bool trace_ignore_this_task(struct trace_pid_list *filtered_pids, diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c index 573b5d8e8a28..cb49f7279dc8 100644 --- a/kernel/trace/trace_sched_switch.c +++ b/kernel/trace/trace_sched_switch.c @@ -442,7 +442,7 @@ int trace_alloc_tgid_map(void) if (tgid_map) return 0; - tgid_map_max = pid_max; + tgid_map_max = init_pid_ns.pid_max; map = kvcalloc(tgid_map_max + 1, sizeof(*tgid_map), GFP_KERNEL); if (!map) From 615ab43b838bb982dc234feff75ee9ad35447c5d Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 22 Nov 2024 14:24:59 +0100 Subject: [PATCH 2/2] tests/pid_namespace: add pid_max tests Signed-off-by: Alexander Mikhalitsyn Link: https://lore.kernel.org/r/20241122132459.135120-3-aleksandr.mikhalitsyn@canonical.com Signed-off-by: Christian Brauner --- .../selftests/pid_namespace/.gitignore | 1 + .../testing/selftests/pid_namespace/Makefile | 2 +- .../testing/selftests/pid_namespace/pid_max.c | 358 ++++++++++++++++++ 3 files changed, 360 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/pid_namespace/pid_max.c diff --git a/tools/testing/selftests/pid_namespace/.gitignore b/tools/testing/selftests/pid_namespace/.gitignore index 93ab9d7e5b7e..5118f0f3edf4 100644 --- a/tools/testing/selftests/pid_namespace/.gitignore +++ b/tools/testing/selftests/pid_namespace/.gitignore @@ -1 +1,2 @@ +pid_max regression_enomem diff --git a/tools/testing/selftests/pid_namespace/Makefile b/tools/testing/selftests/pid_namespace/Makefile index 9286a1d22cd3..b972f55d07ae 100644 --- a/tools/testing/selftests/pid_namespace/Makefile +++ b/tools/testing/selftests/pid_namespace/Makefile @@ -1,7 +1,7 @@ # SPDX-License-Identifier: GPL-2.0 CFLAGS += -g $(KHDR_INCLUDES) -TEST_GEN_PROGS = regression_enomem +TEST_GEN_PROGS = regression_enomem pid_max LOCAL_HDRS += $(selfdir)/pidfd/pidfd.h diff --git a/tools/testing/selftests/pid_namespace/pid_max.c b/tools/testing/selftests/pid_namespace/pid_max.c new file mode 100644 index 000000000000..51c414faabb0 --- /dev/null +++ b/tools/testing/selftests/pid_namespace/pid_max.c @@ -0,0 +1,358 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../kselftest_harness.h" +#include "../pidfd/pidfd.h" + +#define __STACK_SIZE (8 * 1024 * 1024) +static pid_t do_clone(int (*fn)(void *), void *arg, int flags) +{ + char *stack; + pid_t ret; + + stack = malloc(__STACK_SIZE); + if (!stack) + return -ENOMEM; + +#ifdef __ia64__ + ret = __clone2(fn, stack, __STACK_SIZE, flags | SIGCHLD, arg); +#else + ret = clone(fn, stack + __STACK_SIZE, flags | SIGCHLD, arg); +#endif + free(stack); + return ret; +} + +static int pid_max_cb(void *data) +{ + int fd, ret; + pid_t pid; + + ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0); + if (ret) { + fprintf(stderr, "%m - Failed to make rootfs private mount\n"); + return -1; + } + + umount2("/proc", MNT_DETACH); + + ret = mount("proc", "/proc", "proc", 0, NULL); + if (ret) { + fprintf(stderr, "%m - Failed to mount proc\n"); + return -1; + } + + fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY); + if (fd < 0) { + fprintf(stderr, "%m - Failed to open pid_max\n"); + return -1; + } + + ret = write(fd, "500", sizeof("500") - 1); + if (ret < 0) { + fprintf(stderr, "%m - Failed to write pid_max\n"); + return -1; + } + + for (int i = 0; i < 501; i++) { + pid = fork(); + if (pid == 0) + exit(EXIT_SUCCESS); + wait_for_pid(pid); + if (pid > 500) { + fprintf(stderr, "Managed to create pid number beyond limit\n"); + return -1; + } + } + + return 0; +} + +static int pid_max_nested_inner(void *data) +{ + int fret = -1; + pid_t pids[2]; + int fd, i, ret; + + ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0); + if (ret) { + fprintf(stderr, "%m - Failed to make rootfs private mount\n"); + return fret; + } + + umount2("/proc", MNT_DETACH); + + ret = mount("proc", "/proc", "proc", 0, NULL); + if (ret) { + fprintf(stderr, "%m - Failed to mount proc\n"); + return fret; + } + + fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY); + if (fd < 0) { + fprintf(stderr, "%m - Failed to open pid_max\n"); + return fret; + } + + ret = write(fd, "500", sizeof("500") - 1); + close(fd); + if (ret < 0) { + fprintf(stderr, "%m - Failed to write pid_max\n"); + return fret; + } + + pids[0] = fork(); + if (pids[0] < 0) { + fprintf(stderr, "Failed to create first new process\n"); + return fret; + } + + if (pids[0] == 0) + exit(EXIT_SUCCESS); + + pids[1] = fork(); + wait_for_pid(pids[0]); + if (pids[1] >= 0) { + if (pids[1] == 0) + exit(EXIT_SUCCESS); + wait_for_pid(pids[1]); + + fprintf(stderr, "Managed to create process even though ancestor pid namespace had a limit\n"); + return fret; + } + + /* Now make sure that we wrap pids at 400. */ + for (i = 0; i < 510; i++) { + pid_t pid; + + pid = fork(); + if (pid < 0) + return fret; + + if (pid == 0) + exit(EXIT_SUCCESS); + + wait_for_pid(pid); + if (pid >= 500) { + fprintf(stderr, "Managed to create process with pid %d beyond configured limit\n", pid); + return fret; + } + } + + return 0; +} + +static int pid_max_nested_outer(void *data) +{ + int fret = -1, nr_procs = 400; + pid_t pids[1000]; + int fd, i, ret; + pid_t pid; + + ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0); + if (ret) { + fprintf(stderr, "%m - Failed to make rootfs private mount\n"); + return fret; + } + + umount2("/proc", MNT_DETACH); + + ret = mount("proc", "/proc", "proc", 0, NULL); + if (ret) { + fprintf(stderr, "%m - Failed to mount proc\n"); + return fret; + } + + fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY); + if (fd < 0) { + fprintf(stderr, "%m - Failed to open pid_max\n"); + return fret; + } + + ret = write(fd, "400", sizeof("400") - 1); + close(fd); + if (ret < 0) { + fprintf(stderr, "%m - Failed to write pid_max\n"); + return fret; + } + + /* + * Create 397 processes. This leaves room for do_clone() (398) and + * one more 399. So creating another process needs to fail. + */ + for (nr_procs = 0; nr_procs < 396; nr_procs++) { + pid = fork(); + if (pid < 0) + goto reap; + + if (pid == 0) + exit(EXIT_SUCCESS); + + pids[nr_procs] = pid; + } + + pid = do_clone(pid_max_nested_inner, NULL, CLONE_NEWPID | CLONE_NEWNS); + if (pid < 0) { + fprintf(stderr, "%m - Failed to clone nested pidns\n"); + goto reap; + } + + if (wait_for_pid(pid)) { + fprintf(stderr, "%m - Nested pid_max failed\n"); + goto reap; + } + + fret = 0; + +reap: + for (int i = 0; i < nr_procs; i++) + wait_for_pid(pids[i]); + + return fret; +} + +static int pid_max_nested_limit_inner(void *data) +{ + int fret = -1, nr_procs = 400; + int fd, ret; + pid_t pid; + pid_t pids[1000]; + + ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0); + if (ret) { + fprintf(stderr, "%m - Failed to make rootfs private mount\n"); + return fret; + } + + umount2("/proc", MNT_DETACH); + + ret = mount("proc", "/proc", "proc", 0, NULL); + if (ret) { + fprintf(stderr, "%m - Failed to mount proc\n"); + return fret; + } + + fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY); + if (fd < 0) { + fprintf(stderr, "%m - Failed to open pid_max\n"); + return fret; + } + + ret = write(fd, "500", sizeof("500") - 1); + close(fd); + if (ret < 0) { + fprintf(stderr, "%m - Failed to write pid_max\n"); + return fret; + } + + for (nr_procs = 0; nr_procs < 500; nr_procs++) { + pid = fork(); + if (pid < 0) + break; + + if (pid == 0) + exit(EXIT_SUCCESS); + + pids[nr_procs] = pid; + } + + if (nr_procs >= 400) { + fprintf(stderr, "Managed to create processes beyond the configured outer limit\n"); + goto reap; + } + + fret = 0; + +reap: + for (int i = 0; i < nr_procs; i++) + wait_for_pid(pids[i]); + + return fret; +} + +static int pid_max_nested_limit_outer(void *data) +{ + int fd, ret; + pid_t pid; + + ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0); + if (ret) { + fprintf(stderr, "%m - Failed to make rootfs private mount\n"); + return -1; + } + + umount2("/proc", MNT_DETACH); + + ret = mount("proc", "/proc", "proc", 0, NULL); + if (ret) { + fprintf(stderr, "%m - Failed to mount proc\n"); + return -1; + } + + fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY); + if (fd < 0) { + fprintf(stderr, "%m - Failed to open pid_max\n"); + return -1; + } + + ret = write(fd, "400", sizeof("400") - 1); + close(fd); + if (ret < 0) { + fprintf(stderr, "%m - Failed to write pid_max\n"); + return -1; + } + + pid = do_clone(pid_max_nested_limit_inner, NULL, CLONE_NEWPID | CLONE_NEWNS); + if (pid < 0) { + fprintf(stderr, "%m - Failed to clone nested pidns\n"); + return -1; + } + + if (wait_for_pid(pid)) { + fprintf(stderr, "%m - Nested pid_max failed\n"); + return -1; + } + + return 0; +} + +TEST(pid_max_simple) +{ + pid_t pid; + + + pid = do_clone(pid_max_cb, NULL, CLONE_NEWPID | CLONE_NEWNS); + ASSERT_GT(pid, 0); + ASSERT_EQ(0, wait_for_pid(pid)); +} + +TEST(pid_max_nested_limit) +{ + pid_t pid; + + pid = do_clone(pid_max_nested_limit_outer, NULL, CLONE_NEWPID | CLONE_NEWNS); + ASSERT_GT(pid, 0); + ASSERT_EQ(0, wait_for_pid(pid)); +} + +TEST(pid_max_nested) +{ + pid_t pid; + + pid = do_clone(pid_max_nested_outer, NULL, CLONE_NEWPID | CLONE_NEWNS); + ASSERT_GT(pid, 0); + ASSERT_EQ(0, wait_for_pid(pid)); +} + +TEST_HARNESS_MAIN