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Message-ID: <20241120-entgiften-geldhahn-a9d2922ec3e0@brauner>
Date: Wed, 20 Nov 2024 10:06:27 +0100
From: Christian Brauner <brauner@...nel.org>
To: Yun Zhou <yun.zhou@...driver.com>
Cc: stgraber@...raber.org, tycho@...ho.pizza, cyphar@...har.com,
Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>, mcgrof@...nel.org, kees@...nel.org, joel.granados@...nel.org,
mhiramat@...nel.org, mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kernel: add pid_max to pid_namespace
On Tue, Nov 05, 2024 at 11:10:24AM +0800, Yun Zhou wrote:
> It is necessary to have a different pid_max in different containers.
> For example, multiple containers are running on a host, one of which
> is Android, and its 32 bit bionic libc only accepts pid <= 65535. So
> it requires the global pid_max <= 65535. This will cause configuration
> conflicts with other containers and also limit the maximum number of
> tasks for the entire system.
>
> Signed-off-by: Yun Zhou <yun.zhou@...driver.com>
> ---
Fwiw, I've done a patch like this years ago and then Alex revived it in
[1] including selftests! There's downsides to consider:
[1]: https://lore.kernel.org/lkml/20240222160915.315255-1-aleksandr.mikhalitsyn@canonical.com
> - Remove sentinels from ctl_table arrays.
> v1 - https://lore.kernel.org/all/20241030052933.1041408-1-yun.zhou@windriver.com/
> ---
> include/linux/pid_namespace.h | 1 +
> kernel/pid.c | 12 +++++------
> kernel/pid_namespace.c | 34 ++++++++++++++++++++++++++-----
> kernel/sysctl.c | 9 --------
> kernel/trace/pid_list.c | 2 +-
> kernel/trace/trace.h | 2 --
> kernel/trace/trace_sched_switch.c | 2 +-
> 7 files changed, 38 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index f9f9931e02d6..064cfe2542fc 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -38,6 +38,7 @@ struct pid_namespace {
> struct ucounts *ucounts;
> int reboot; /* group exit code if this pidns was rebooted */
> struct ns_common ns;
> + int pid_max;
> #if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> int memfd_noexec_scope;
> #endif
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 2715afb77eab..f8026a61436b 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -60,8 +60,6 @@ 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;
> /*
> @@ -78,6 +76,7 @@ static u64 pidfs_ino = RESERVED_PIDS;
> */
> struct pid_namespace init_pid_ns = {
> .ns.count = REFCOUNT_INIT(2),
> + .pid_max = PID_MAX_DEFAULT,
> .idr = IDR_INIT(init_pid_ns.idr),
> .pid_allocated = PIDNS_ADDING,
> .level = 0,
> @@ -198,7 +197,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> tid = set_tid[ns->level - i];
>
> retval = -EINVAL;
> - if (tid < 1 || tid >= pid_max)
> + if (tid < 1 || tid >= tmp->pid_max)
> goto out_free;
> /*
> * Also fail if a PID != 1 is requested and
> @@ -238,7 +237,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> * a partially initialized PID (see below).
> */
> nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
> - pid_max, GFP_ATOMIC);
> + tmp->pid_max, GFP_ATOMIC);
> }
> spin_unlock_irq(&pidmap_lock);
> idr_preload_end();
> @@ -653,11 +652,12 @@ void __init pid_idr_init(void)
> 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,
> + 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);
>
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index d70ab49d5b4a..a5a8254825d5 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -111,6 +111,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> ns->user_ns = get_user_ns(user_ns);
> ns->ucounts = ucounts;
> ns->pid_allocated = PIDNS_ADDING;
> + ns->pid_max = parent_pid_ns->pid_max;
> #if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> ns->memfd_noexec_scope = pidns_memfd_noexec_scope(parent_pid_ns);
> #endif
> @@ -280,19 +281,44 @@ static int pid_ns_ctl_handler(const struct ctl_table *table, int write,
>
> return ret;
> }
> +#endif /* CONFIG_CHECKPOINT_RESTORE */
> +
> +static int pid_max_ns_ctl_handler(const struct ctl_table *table, int write,
> + void *buffer, size_t *lenp, loff_t *ppos)
> +{
> + struct pid_namespace *pid_ns = task_active_pid_ns(current);
> + struct ctl_table tmp = *table;
> +
> + if (write && !checkpoint_restore_ns_capable(pid_ns->user_ns))
> + return -EPERM;
> +
> + tmp.data = &pid_ns->pid_max;
> + if (pid_ns->parent)
> + tmp.extra2 = &pid_ns->parent->pid_max;
> +
> + return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
> +}
>
> -extern int pid_max;
> static struct ctl_table pid_ns_ctl_table[] = {
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> {
> .procname = "ns_last_pid",
> .maxlen = sizeof(int),
> .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 */
> + {
> + .procname = "pid_max",
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = pid_max_ns_ctl_handler,
> + .extra1 = &pid_max_min,
> + .extra2 = &pid_max_max,
> + },
> +};
>
> int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
> {
> @@ -449,9 +475,7 @@ static __init int pid_namespaces_init(void)
> {
> pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC | SLAB_ACCOUNT);
>
> -#ifdef CONFIG_CHECKPOINT_RESTORE
> register_sysctl_init("kernel", pid_ns_ctl_table);
> -#endif
>
> register_pid_ns_sysctl_table_vm();
> return 0;
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 79e6cb1d5c48..676a0d675e7f 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1804,15 +1804,6 @@ 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 c866991b9c78..e51851d64e4d 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -715,8 +715,6 @@ 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 8a407adb0e1c..c20c80abe065 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)
> --
> 2.27.0
>
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