[RFC PATCH 03/27] containers: Provide /proc/containers

David Howells
2019-02-15T16:07:51Z

Provide /proc/containers to view the current container and all the
containers created within it:

# ./foo-container
NAME USE FL OWNER GROUP
<current> 141 01 0 0
foo-test 1 04 0 0

I'm not sure whether this is really desirable, though.

Signed-off-by: David Howells <dhowells@redhat.com>
---

kernel/container.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 110 insertions(+)

diff --git a/kernel/container.c b/kernel/container.c
index ca4012632cfa..1d2cb1c1e9b1 100644
--- a/kernel/container.c
+++ b/kernel/container.c
@@ -20,6 +20,7 @@
#include <linux/syscalls.h>
#include <linux/printk.h>
#include <linux/security.h>
+#include <linux/proc_fs.h>
#include "namespaces.h"

struct container init_container = {
@@ -69,6 +70,108 @@ void put_container(struct container *c)
}
}

+static void *container_proc_start(struct seq_file *m, loff_t *_pos)
+{
+ struct container *c = m->private;
+ struct list_head *p;
+ loff_t pos = *_pos;
+
+ spin_lock(&c->lock);
+
+ if (pos <= 1) {
+ *_pos = 1;
+ return (void *)1UL; /* Banner on first line */
+ }
+
+ if (pos == 2)
+ return m->private; /* Current container on second line */
+
+ /* Subordinate containers thereafter */
+ p = c->children.next;
+ pos--;
+ for (pos--; pos > 0 && p != &c->children; pos--) {
+ p = p->next;
+ }
+
+ if (p == &c->children)
+ return NULL;
+ return container_of(p, struct container, child_link);
+}
+
+static void *container_proc_next(struct seq_file *m, void *v, loff_t *_pos)
+{
+ struct container *c = m->private, *vc = v;
+ struct list_head *p;
+ loff_t pos = *_pos;
+
+ pos++;
+ *_pos = pos;
+ if (pos == 2)
+ return c; /* Current container on second line */
+
+ if (pos == 3)
+ p = &c->children;
+ else
+ p = &vc->child_link;
+ p = p->next;
+ if (p == &c->children)
+ return NULL;
+ return container_of(p, struct container, child_link);
+}
+
+static void container_proc_stop(struct seq_file *m, void *v)
+{
+ struct container *c = m->private;
+
+ spin_unlock(&c->lock);
+}
+
+static int container_proc_show(struct seq_file *m, void *v)
+{
+ struct user_namespace *uns = current_user_ns();
+ struct container *c = v;
+ const char *name;
+
+ if (v == (void *)1UL) {
+ seq_puts(m, "NAME ID USE FL OWNER GROUP\n");
+ return 0;
+ }
+
+ name = (c == m->private) ? "<current>" : c->name;
+ seq_printf(m, "%-24s %12llu %3u %02lx %5d %5d\n",
+ name, c->id, refcount_read(&c->usage), c->flags,
+ from_kuid_munged(uns, c->cred->uid),
+ from_kgid_munged(uns, c->cred->gid));
+
+ return 0;
+}
+
+static const struct seq_operations container_proc_ops = {
+ .start = container_proc_start,
+ .next = container_proc_next,
+ .stop = container_proc_stop,
+ .show = container_proc_show,
+};
+
+static int container_proc_open(struct inode *inode, struct file *file)
+{
+ struct seq_file *m;
+ int ret = seq_open(file, &container_proc_ops);
+
+ if (ret == 0) {
+ m = file->private_data;
+ m->private = current->container;
+ }
+ return ret;
+}
+
+static const struct file_operations container_proc_fops = {
+ .open = container_proc_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
/*
* Allow the user to poll for the container dying.
*/
@@ -345,4 +448,11 @@ SYSCALL_DEFINE5(container_create,
return fd;
}

+static int __init init_container_fs(void)
+{
+ proc_create("containers", 0, NULL, &container_proc_fops);
+ return 0;
+}
+fs_initcall(init_container_fs);
+
#endif /* CONFIG_CONTAINERS */