// SPDX-License-Identifier: GPL-2.0
#include <linux/cache.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/pid_namespace.h>
#include "internal.h"

/*
 * /proc/self:
 */
static const char *proc_self_get_link(struct dentry *dentry,
                                      struct inode *inode,
                                      struct delayed_call *done)
{
        struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
        pid_t tgid = task_tgid_nr_ns(current, ns);
        char *name;

        if (!tgid)
                return ERR_PTR(-ENOENT);
        /* max length of unsigned int in decimal + NULL term */
        name = kmalloc(10 + 1, dentry ? GFP_KERNEL : GFP_ATOMIC);
        if (unlikely(!name))
                return dentry ? ERR_PTR(-ENOMEM) : ERR_PTR(-ECHILD);
        sprintf(name, "%u", tgid);
        set_delayed_call(done, kfree_link, name);
        return name;
}

static const struct inode_operations proc_self_inode_operations = {
        .get_link       = proc_self_get_link,
};

unsigned self_inum __ro_after_init;

int proc_setup_self(struct super_block *s)
{
        struct inode *root_inode = d_inode(s->s_root);
        struct dentry *self;
        int ret = -ENOMEM;

        inode_lock(root_inode);
        self = d_alloc_name(s->s_root, "self");
        if (self) {
                struct inode *inode = new_inode(s);
                if (inode) {
                        inode->i_ino = self_inum;
                        simple_inode_init_ts(inode);
                        inode->i_mode = S_IFLNK | S_IRWXUGO;
                        inode->i_uid = GLOBAL_ROOT_UID;
                        inode->i_gid = GLOBAL_ROOT_GID;
                        inode->i_op = &proc_self_inode_operations;
                        d_make_persistent(self, inode);
                        ret = 0;
                }
                dput(self);
        }
        inode_unlock(root_inode);

        if (ret)
                pr_err("proc_fill_super: can't allocate /proc/self\n");

        return ret;
}

void __init proc_self_init(void)
{
        proc_alloc_inum(&self_inum);
}