Re: [RESEND RFC] translate_pid API
From: Jann Horn <jannh@google.com>
Date: 2018-03-13 20:48:06
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lkml
On Mon, Mar 12, 2018 at 10:18 AM, [off-list ref] wrote:
Resending the RFC with participants of previous discussions in the list. Following patch which is a variation of a solution discussed in https://lwn.net/Articles/736330/ provides the users of pid namespace, the functionality of pid translation between namespaces using a namespace identifier. The topic of pid translation has been discussed in the community few times but there has always been a resistance to adding new solution for this problem.
I will outline the planned usecase of pid namespace by oracle database and explain why any of the existing solution cannot be used to solve their problem. Consider a system in which several PID namespaces with multiple nested levels exists in parallel with monitor processes managing all the namespaces. PID translation is required for controlling and accessing information about the processes by the monitors and other processes down the hierarchy of namespaces. Controlling primarily involves sending signals or using ptrace by a process in parent namespace on any of the processes in its child namespace. Accessing information deals with the reading /proc/<pid>/* files of processes in child namespace. None of the processes have root/CAP_SYS_ADMIN privileges.
How are you dealing with PID reuse? [...]
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diff --git a/fs/nsfs.c b/fs/nsfs.c index 36b0772..c635465 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c@@ -222,8 +222,13 @@ int ns_get_name(char *buf, size_t size, struct task_struct *task, const char *name; ns = ns_ops->get(task); if (ns) { - name = ns_ops->real_ns_name ? : ns_ops->name; - res = snprintf(buf, size, "%s:[%u]", name, ns->inum); + if (!strcmp(ns_ops->name, "pidns_id")) {
Wouldn't it be cleaner to check for "ns_ops==&pidns_id_operations"?
+ res = snprintf(buf, size, "[%llu]",
+ (unsigned long long)ns->ns_id);
+ } else {
+ name = ns_ops->real_ns_name ? : ns_ops->name;
+ res = snprintf(buf, size, "%s:[%u]", name, ns->inum);
+ }
ns_ops->put(ns);
}
return res;[...]
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diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h index 49538b1..11d1d57 100644 --- a/include/linux/pid_namespace.h +++ b/include/linux/pid_namespace.h@@ -11,6 +11,7 @@ #include <linux/kref.h> #include <linux/ns_common.h> #include <linux/idr.h> +#include <linux/list_bl.h> struct fs_pin;@@ -44,6 +45,8 @@ struct pid_namespace { kgid_t pid_gid; int hide_pid; int reboot; /* group exit code if this pidns was rebooted */ + struct hlist_bl_node node; + atomic_t lookups_pending; struct ns_common ns; } __randomize_layout;
[...]
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diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index 0b53eef..ff83aa8 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c
[...]
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@@ -159,6 +201,30 @@ static void delayed_free_pidns(struct rcu_head *p) static void destroy_pid_namespace(struct pid_namespace *ns) { + struct pid_namespace *ph; + struct hlist_bl_head *head; + struct hlist_bl_node *dup_node; + + /* + * Remove the namespace structure from hash table so + * now new lookups can start on it.
s/now new/no new/ [...]
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@@ -474,9 +551,116 @@ static struct user_namespace *pidns_owner(struct ns_common *ns) .get_parent = pidns_get_parent, }; +/* + * translate_pid - convert pid in source pid-ns into target pid-ns. + * @pid: pid for translation + * @source: pid-ns id + * @target: pid-ns id + * + * Return pid in @target pid-ns, zero if task have no pid there, + * or -ESRCH of task with @pid is not found in @source pid-ns.
s/of/if/
+ */
+SYSCALL_DEFINE3(translate_pid, pid_t, pid, u64, source,
+ u64, target)
+{
+ struct pid_namespace *source_ns = NULL, *target_ns = NULL;
+ struct pid *struct_pid;
+ struct pid_namespace *ph;
+ struct hlist_bl_head *shead = NULL;
+ struct hlist_bl_head *thead = NULL;
+ struct hlist_bl_node *dup_node;
+ pid_t result;
+
+ if (!source) {
+ source_ns = &init_pid_ns;
+ } else {
+ shead = pid_ns_hash_head(pid_ns_hash, source);
+ hlist_bl_lock(shead);
+ hlist_bl_for_each_entry(ph, dup_node, shead, node) {
+ if (source == ph->ns.ns_id) {
+ source_ns = ph;
+ break;
+ }
+ }
+ if (!source_ns) {
+ hlist_bl_unlock(shead);
+ return -EINVAL;
+ }
+ }
+ if (!ptrace_may_access(source_ns->child_reaper,
+ PTRACE_MODE_READ_FSCREDS)) {AFAICS this proposal breaks the visibility restrictions that namespaces normally create. If there are two namespaces-based containers that use the same UID range, I don't think they should be able to learn information about each other, such as which PIDs are in use in the other container; but as far as I can tell, your proposal makes it possible to do that (unless an LSM or so is interfering). I would prefer it if this API required visibility of the targeted PID namespaces in the caller's PID namespace. When doing ptrace access checks, please use the real creds in syscalls like this one, not the fs creds. The fs creds are for filesystem syscalls (in particular sys_open()), not for specialized syscalls like ptrace() or this one.