// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/proc/root.c
 *
 *  Copyright (C) 1991, 1992 Linus Torvalds
 *
 *  proc root directory handling functions
 */
#include <linux/errno.h>
#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/sched/stat.h>
#include <linux/module.h>
#include <linux/bitops.h>
#include <linux/user_namespace.h>
#include <linux/fs_context.h>
#include <linux/mount.h>
#include <linux/pid_namespace.h>
#include <linux/fs_parser.h>
#include <linux/cred.h>
#include <linux/magic.h>
#include <linux/slab.h>

#include "internal.h"

struct proc_fs_context {
        struct pid_namespace    *pid_ns;
        unsigned int            mask;
        enum proc_hidepid       hidepid;
        int                     gid;
        enum proc_pidonly       pidonly;
};

enum proc_param {
        Opt_gid,
        Opt_hidepid,
        Opt_subset,
        Opt_pidns,
};

static const struct fs_parameter_spec proc_fs_parameters[] = {
        fsparam_u32("gid",              Opt_gid),
        fsparam_string("hidepid",       Opt_hidepid),
        fsparam_string("subset",        Opt_subset),
        fsparam_file_or_string("pidns", Opt_pidns),
        {}
};

static inline int valid_hidepid(unsigned int value)
{
        return (value == HIDEPID_OFF ||
                value == HIDEPID_NO_ACCESS ||
                value == HIDEPID_INVISIBLE ||
                value == HIDEPID_NOT_PTRACEABLE);
}

static int proc_parse_hidepid_param(struct fs_context *fc, struct fs_parameter *param)
{
        struct proc_fs_context *ctx = fc->fs_private;
        struct fs_parameter_spec hidepid_u32_spec = fsparam_u32("hidepid", Opt_hidepid);
        struct fs_parse_result result;
        int base = (unsigned long)hidepid_u32_spec.data;

        if (param->type != fs_value_is_string)
                return invalf(fc, "proc: unexpected type of hidepid value\n");

        if (!kstrtouint(param->string, base, &result.uint_32)) {
                if (!valid_hidepid(result.uint_32))
                        return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string);
                ctx->hidepid = result.uint_32;
                return 0;
        }

        if (!strcmp(param->string, "off"))
                ctx->hidepid = HIDEPID_OFF;
        else if (!strcmp(param->string, "noaccess"))
                ctx->hidepid = HIDEPID_NO_ACCESS;
        else if (!strcmp(param->string, "invisible"))
                ctx->hidepid = HIDEPID_INVISIBLE;
        else if (!strcmp(param->string, "ptraceable"))
                ctx->hidepid = HIDEPID_NOT_PTRACEABLE;
        else
                return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string);

        return 0;
}

static int proc_parse_subset_param(struct fs_context *fc, char *value)
{
        struct proc_fs_context *ctx = fc->fs_private;

        while (value) {
                char *ptr = strchr(value, ',');

                if (ptr != NULL)
                        *ptr++ = '\0';

                if (*value != '\0') {
                        if (!strcmp(value, "pid")) {
                                ctx->pidonly = PROC_PIDONLY_ON;
                        } else {
                                return invalf(fc, "proc: unsupported subset option - %s\n", value);
                        }
                }
                value = ptr;
        }

        return 0;
}

#ifdef CONFIG_PID_NS
static int proc_parse_pidns_param(struct fs_context *fc,
                                  struct fs_parameter *param,
                                  struct fs_parse_result *result)
{
        struct proc_fs_context *ctx = fc->fs_private;
        struct pid_namespace *target, *active = task_active_pid_ns(current);
        struct ns_common *ns;
        struct file *ns_filp __free(fput) = NULL;

        switch (param->type) {
        case fs_value_is_file:
                /* came through fsconfig, steal the file reference */
                ns_filp = no_free_ptr(param->file);
                break;
        case fs_value_is_string:
                ns_filp = filp_open(param->string, O_RDONLY, 0);
                break;
        default:
                WARN_ON_ONCE(true);
                break;
        }
        if (!ns_filp)
                ns_filp = ERR_PTR(-EBADF);
        if (IS_ERR(ns_filp)) {
                errorfc(fc, "could not get file from pidns argument");
                return PTR_ERR(ns_filp);
        }

        if (!proc_ns_file(ns_filp))
                return invalfc(fc, "pidns argument is not an nsfs file");
        ns = get_proc_ns(file_inode(ns_filp));
        if (ns->ns_type != CLONE_NEWPID)
                return invalfc(fc, "pidns argument is not a pidns file");
        target = container_of(ns, struct pid_namespace, ns);

        /*
         * pidns= is shorthand for joining the pidns to get a fsopen fd, so the
         * permission model should be the same as pidns_install().
         */
        if (!ns_capable(target->user_ns, CAP_SYS_ADMIN)) {
                errorfc(fc, "insufficient permissions to set pidns");
                return -EPERM;
        }
        if (!pidns_is_ancestor(target, active))
                return invalfc(fc, "cannot set pidns to non-descendant pidns");

        put_pid_ns(ctx->pid_ns);
        ctx->pid_ns = get_pid_ns(target);
        put_user_ns(fc->user_ns);
        fc->user_ns = get_user_ns(ctx->pid_ns->user_ns);
        return 0;
}
#endif /* CONFIG_PID_NS */

static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
        struct proc_fs_context *ctx = fc->fs_private;
        struct fs_parse_result result;
        int opt, err;

        opt = fs_parse(fc, proc_fs_parameters, param, &result);
        if (opt < 0)
                return opt;

        switch (opt) {
        case Opt_gid:
                ctx->gid = result.uint_32;
                break;

        case Opt_hidepid:
                err = proc_parse_hidepid_param(fc, param);
                if (err)
                        return err;
                break;

        case Opt_subset:
                err = proc_parse_subset_param(fc, param->string);
                if (err)
                        return err;
                break;

        case Opt_pidns:
#ifdef CONFIG_PID_NS
                /*
                 * We would have to RCU-protect every proc_pid_ns() or
                 * proc_sb_info() access if we allowed this to be reconfigured
                 * for an existing procfs instance. Luckily, procfs instances
                 * are cheap to create, and mount-beneath would let you
                 * atomically replace an instance even with overmounts.
                 */
                if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE) {
                        errorfc(fc, "cannot reconfigure pidns for existing procfs");
                        return -EBUSY;
                }
                err = proc_parse_pidns_param(fc, param, &result);
                if (err)
                        return err;
                break;
#else
                errorfc(fc, "pidns mount flag not supported on this system");
                return -EOPNOTSUPP;
#endif

        default:
                return -EINVAL;
        }

        ctx->mask |= 1 << opt;
        return 0;
}

static void proc_apply_options(struct proc_fs_info *fs_info,
                               struct fs_context *fc,
                               struct user_namespace *user_ns)
{
        struct proc_fs_context *ctx = fc->fs_private;

        if (ctx->mask & (1 << Opt_gid))
                fs_info->pid_gid = make_kgid(user_ns, ctx->gid);
        if (ctx->mask & (1 << Opt_hidepid))
                fs_info->hide_pid = ctx->hidepid;
        if (ctx->mask & (1 << Opt_subset))
                fs_info->pidonly = ctx->pidonly;
        if (ctx->mask & (1 << Opt_pidns) &&
            !WARN_ON_ONCE(fc->purpose == FS_CONTEXT_FOR_RECONFIGURE)) {
                put_pid_ns(fs_info->pid_ns);
                fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
        }
}

static int proc_fill_super(struct super_block *s, struct fs_context *fc)
{
        struct proc_fs_context *ctx = fc->fs_private;
        struct inode *root_inode;
        struct proc_fs_info *fs_info;
        int ret;

        fs_info = kzalloc_obj(*fs_info);
        if (!fs_info)
                return -ENOMEM;

        fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
        proc_apply_options(fs_info, fc, current_user_ns());

        /* User space would break if executables or devices appear on proc */
        s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
        s->s_flags |= SB_NODIRATIME | SB_NOSUID | SB_NOEXEC;
        s->s_blocksize = 1024;
        s->s_blocksize_bits = 10;
        s->s_magic = PROC_SUPER_MAGIC;
        s->s_op = &proc_sops;
        s->s_time_gran = 1;
        s->s_fs_info = fs_info;

        /*
         * procfs isn't actually a stacking filesystem; however, there is
         * too much magic going on inside it to permit stacking things on
         * top of it
         */
        s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;

        /* procfs dentries and inodes don't require IO to create */
        s->s_shrink->seeks = 0;

        pde_get(&proc_root);
        root_inode = proc_get_inode(s, &proc_root);
        if (!root_inode) {
                pr_err("proc_fill_super: get root inode failed\n");
                return -ENOMEM;
        }

        s->s_root = d_make_root(root_inode);
        if (!s->s_root) {
                pr_err("proc_fill_super: allocate dentry failed\n");
                return -ENOMEM;
        }

        ret = proc_setup_self(s);
        if (ret) {
                return ret;
        }
        return proc_setup_thread_self(s);
}

static int proc_reconfigure(struct fs_context *fc)
{
        struct super_block *sb = fc->root->d_sb;
        struct proc_fs_info *fs_info = proc_sb_info(sb);

        sync_filesystem(sb);

        proc_apply_options(fs_info, fc, current_user_ns());
        return 0;
}

static int proc_get_tree(struct fs_context *fc)
{
        return get_tree_nodev(fc, proc_fill_super);
}

static void proc_fs_context_free(struct fs_context *fc)
{
        struct proc_fs_context *ctx = fc->fs_private;

        put_pid_ns(ctx->pid_ns);
        kfree(ctx);
}

static const struct fs_context_operations proc_fs_context_ops = {
        .free           = proc_fs_context_free,
        .parse_param    = proc_parse_param,
        .get_tree       = proc_get_tree,
        .reconfigure    = proc_reconfigure,
};

static int proc_init_fs_context(struct fs_context *fc)
{
        struct proc_fs_context *ctx;

        ctx = kzalloc_obj(struct proc_fs_context);
        if (!ctx)
                return -ENOMEM;

        ctx->pid_ns = get_pid_ns(task_active_pid_ns(current));
        put_user_ns(fc->user_ns);
        fc->user_ns = get_user_ns(ctx->pid_ns->user_ns);
        fc->fs_private = ctx;
        fc->ops = &proc_fs_context_ops;
        return 0;
}

static void proc_kill_sb(struct super_block *sb)
{
        struct proc_fs_info *fs_info = proc_sb_info(sb);

        kill_anon_super(sb);
        if (fs_info) {
                put_pid_ns(fs_info->pid_ns);
                kfree_rcu(fs_info, rcu);
        }
}

static struct file_system_type proc_fs_type = {
        .name                   = "proc",
        .init_fs_context        = proc_init_fs_context,
        .parameters             = proc_fs_parameters,
        .kill_sb                = proc_kill_sb,
        .fs_flags               = FS_USERNS_MOUNT | FS_DISALLOW_NOTIFY_PERM,
};

void __init proc_root_init(void)
{
        proc_init_kmemcache();
        set_proc_pid_nlink();
        proc_self_init();
        proc_thread_self_init();
        proc_symlink("mounts", NULL, "self/mounts");

        proc_net_init();
        proc_mkdir("fs", NULL);
        proc_mkdir("driver", NULL);
        proc_create_mount_point("fs/nfsd"); /* somewhere for the nfsd filesystem to be mounted */
#if defined(CONFIG_SUN_OPENPROMFS) || defined(CONFIG_SUN_OPENPROMFS_MODULE)
        /* just give it a mountpoint */
        proc_create_mount_point("openprom");
#endif
        proc_tty_init();
        proc_mkdir("bus", NULL);
        proc_sys_init();

        /*
         * Last things last. It is not like userspace processes eager
         * to open /proc files exist at this point but register last
         * anyway.
         */
        register_filesystem(&proc_fs_type);
}

static int proc_root_getattr(struct mnt_idmap *idmap,
                             const struct path *path, struct kstat *stat,
                             u32 request_mask, unsigned int query_flags)
{
        generic_fillattr(&nop_mnt_idmap, request_mask, d_inode(path->dentry),
                         stat);
        stat->nlink = proc_root.nlink + nr_processes();
        return 0;
}

static struct dentry *proc_root_lookup(struct inode * dir, struct dentry * dentry, unsigned int flags)
{
        if (!proc_pid_lookup(dentry, flags))
                return NULL;

        return proc_lookup(dir, dentry, flags);
}

static int proc_root_readdir(struct file *file, struct dir_context *ctx)
{
        if (ctx->pos < FIRST_PROCESS_ENTRY) {
                int error = proc_readdir(file, ctx);
                if (unlikely(error <= 0))
                        return error;
                ctx->pos = FIRST_PROCESS_ENTRY;
        }

        return proc_pid_readdir(file, ctx);
}

/*
 * The root /proc directory is special, as it has the
 * <pid> directories. Thus we don't use the generic
 * directory handling functions for that..
 */
static const struct file_operations proc_root_operations = {
        .read            = generic_read_dir,
        .iterate_shared  = proc_root_readdir,
        .llseek         = generic_file_llseek,
};

/*
 * proc root can do almost nothing..
 */
static const struct inode_operations proc_root_inode_operations = {
        .lookup         = proc_root_lookup,
        .getattr        = proc_root_getattr,
};

/*
 * This is the root "inode" in the /proc tree..
 */
struct proc_dir_entry proc_root = {
        .low_ino        = PROCFS_ROOT_INO,
        .namelen        = 5,
        .mode           = S_IFDIR | S_IRUGO | S_IXUGO,
        .nlink          = 2,
        .refcnt         = REFCOUNT_INIT(1),
        .proc_iops      = &proc_root_inode_operations,
        .proc_dir_ops   = &proc_root_operations,
        .parent         = &proc_root,
        .subdir         = RB_ROOT,
        .name           = "/proc",
};