// SPDX-License-Identifier: GPL-2.0-only
/*
 * linux/fs/nfs/namespace.c
 *
 * Copyright (C) 2005 Trond Myklebust <Trond.Myklebust@netapp.com>
 * - Modified by David Howells <dhowells@redhat.com>
 *
 * NFS namespace
 */

#include <linux/module.h>
#include <linux/dcache.h>
#include <linux/gfp.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/nfs_fs.h>
#include <linux/string.h>
#include <linux/sunrpc/clnt.h>
#include <linux/vfs.h>
#include <linux/sunrpc/gss_api.h>
#include "internal.h"
#include "nfs.h"

#define NFSDBG_FACILITY         NFSDBG_VFS

static void nfs_expire_automounts(struct work_struct *work);

static LIST_HEAD(nfs_automount_list);
static DECLARE_DELAYED_WORK(nfs_automount_task, nfs_expire_automounts);
int nfs_mountpoint_expiry_timeout = 500 * HZ;

/*
 * nfs_path - reconstruct the path given an arbitrary dentry
 * @base - used to return pointer to the end of devname part of path
 * @dentry_in - pointer to dentry
 * @buffer - result buffer
 * @buflen_in - length of buffer
 * @flags - options (see below)
 *
 * Helper function for constructing the server pathname
 * by arbitrary hashed dentry.
 *
 * This is mainly for use in figuring out the path on the
 * server side when automounting on top of an existing partition
 * and in generating /proc/mounts and friends.
 *
 * Supported flags:
 * NFS_PATH_CANONICAL: ensure there is exactly one slash after
 *                     the original device (export) name
 *                     (if unset, the original name is returned verbatim)
 */
char *nfs_path(char **p, struct dentry *dentry_in, char *buffer,
               ssize_t buflen_in, unsigned flags)
{
        char *end;
        int namelen;
        unsigned seq;
        const char *base;
        struct dentry *dentry;
        ssize_t buflen;

rename_retry:
        buflen = buflen_in;
        dentry = dentry_in;
        end = buffer+buflen;
        *--end = '\0';
        buflen--;

        seq = read_seqbegin(&rename_lock);
        rcu_read_lock();
        while (1) {
                spin_lock(&dentry->d_lock);
                if (IS_ROOT(dentry))
                        break;
                namelen = dentry->d_name.len;
                buflen -= namelen + 1;
                if (buflen < 0)
                        goto Elong_unlock;
                end -= namelen;
                memcpy(end, dentry->d_name.name, namelen);
                *--end = '/';
                spin_unlock(&dentry->d_lock);
                dentry = dentry->d_parent;
        }
        if (read_seqretry(&rename_lock, seq)) {
                spin_unlock(&dentry->d_lock);
                rcu_read_unlock();
                goto rename_retry;
        }
        if ((flags & NFS_PATH_CANONICAL) && *end != '/') {
                if (--buflen < 0) {
                        spin_unlock(&dentry->d_lock);
                        rcu_read_unlock();
                        goto Elong;
                }
                *--end = '/';
        }
        *p = end;
        base = dentry->d_fsdata;
        if (!base) {
                spin_unlock(&dentry->d_lock);
                rcu_read_unlock();
                WARN_ON(1);
                return end;
        }
        namelen = strlen(base);
        if (*end == '/') {
                /* Strip off excess slashes in base string */
                while (namelen > 0 && base[namelen - 1] == '/')
                        namelen--;
        }
        buflen -= namelen;
        if (buflen < 0) {
                spin_unlock(&dentry->d_lock);
                rcu_read_unlock();
                goto Elong;
        }
        end -= namelen;
        memcpy(end, base, namelen);
        spin_unlock(&dentry->d_lock);
        rcu_read_unlock();
        return end;
Elong_unlock:
        spin_unlock(&dentry->d_lock);
        rcu_read_unlock();
        if (read_seqretry(&rename_lock, seq))
                goto rename_retry;
Elong:
        return ERR_PTR(-ENAMETOOLONG);
}
EXPORT_SYMBOL_GPL(nfs_path);

/*
 * nfs_d_automount - Handle crossing a mountpoint on the server
 * @path - The mountpoint
 *
 * When we encounter a mountpoint on the server, we want to set up
 * a mountpoint on the client too, to prevent inode numbers from
 * colliding, and to allow "df" to work properly.
 * On NFSv4, we also want to allow for the fact that different
 * filesystems may be migrated to different servers in a failover
 * situation, and that different filesystems may want to use
 * different security flavours.
 */
struct vfsmount *nfs_d_automount(struct path *path)
{
        struct nfs_fs_context *ctx;
        struct fs_context *fc;
        struct vfsmount *mnt = ERR_PTR(-ENOMEM);
        struct nfs_server *server = NFS_SERVER(d_inode(path->dentry));
        struct nfs_client *client = server->nfs_client;
        int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
        int ret;

        if (IS_ROOT(path->dentry))
                return ERR_PTR(-ESTALE);

        /* Open a new filesystem context, transferring parameters from the
         * parent superblock, including the network namespace.
         */
        fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, path->dentry);
        if (IS_ERR(fc))
                return ERR_CAST(fc);

        ctx = nfs_fc2context(fc);
        ctx->clone_data.dentry  = path->dentry;
        ctx->clone_data.sb      = path->dentry->d_sb;
        ctx->clone_data.fattr   = nfs_alloc_fattr();
        if (!ctx->clone_data.fattr)
                goto out_fc;

        if (fc->net_ns != client->cl_net) {
                put_net(fc->net_ns);
                fc->net_ns = get_net(client->cl_net);
        }

        /* for submounts we want the same server; referrals will reassign */
        memcpy(&ctx->nfs_server.address, &client->cl_addr, client->cl_addrlen);
        ctx->nfs_server.addrlen = client->cl_addrlen;
        ctx->nfs_server.port    = server->port;

        ctx->version            = client->rpc_ops->version;
        ctx->minorversion       = client->cl_minorversion;
        ctx->nfs_mod            = client->cl_nfs_mod;
        __module_get(ctx->nfs_mod->owner);

        ret = client->rpc_ops->submount(fc, server);
        if (ret < 0) {
                mnt = ERR_PTR(ret);
                goto out_fc;
        }

        up_write(&fc->root->d_sb->s_umount);
        mnt = vfs_create_mount(fc);
        if (IS_ERR(mnt))
                goto out_fc;

        mntget(mnt); /* prevent immediate expiration */
        if (timeout <= 0)
                goto out_fc;

        mnt_set_expiry(mnt, &nfs_automount_list);
        schedule_delayed_work(&nfs_automount_task, timeout);

out_fc:
        put_fs_context(fc);
        return mnt;
}

static int
nfs_namespace_getattr(struct user_namespace *mnt_userns,
                      const struct path *path, struct kstat *stat,
                      u32 request_mask, unsigned int query_flags)
{
        if (NFS_FH(d_inode(path->dentry))->size != 0)
                return nfs_getattr(mnt_userns, path, stat, request_mask,
                                   query_flags);
        generic_fillattr(&init_user_ns, d_inode(path->dentry), stat);
        return 0;
}

static int
nfs_namespace_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
                      struct iattr *attr)
{
        if (NFS_FH(d_inode(dentry))->size != 0)
                return nfs_setattr(mnt_userns, dentry, attr);
        return -EACCES;
}

const struct inode_operations nfs_mountpoint_inode_operations = {
        .getattr        = nfs_getattr,
        .setattr        = nfs_setattr,
};

const struct inode_operations nfs_referral_inode_operations = {
        .getattr        = nfs_namespace_getattr,
        .setattr        = nfs_namespace_setattr,
};

static void nfs_expire_automounts(struct work_struct *work)
{
        struct list_head *list = &nfs_automount_list;
        int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);

        mark_mounts_for_expiry(list);
        if (!list_empty(list) && timeout > 0)
                schedule_delayed_work(&nfs_automount_task, timeout);
}

void nfs_release_automount_timer(void)
{
        if (list_empty(&nfs_automount_list))
                cancel_delayed_work(&nfs_automount_task);
}

/**
 * nfs_do_submount - set up mountpoint when crossing a filesystem boundary
 * @fc: pointer to struct nfs_fs_context
 *
 */
int nfs_do_submount(struct fs_context *fc)
{
        struct nfs_fs_context *ctx = nfs_fc2context(fc);
        struct dentry *dentry = ctx->clone_data.dentry;
        struct nfs_server *server;
        char *buffer, *p;
        int ret;

        /* create a new volume representation */
        server = ctx->nfs_mod->rpc_ops->clone_server(NFS_SB(ctx->clone_data.sb),
                                                     ctx->mntfh,
                                                     ctx->clone_data.fattr,
                                                     ctx->selected_flavor);

        if (IS_ERR(server))
                return PTR_ERR(server);

        ctx->server = server;

        buffer = kmalloc(4096, GFP_USER);
        if (!buffer)
                return -ENOMEM;

        ctx->internal           = true;
        ctx->clone_data.inherited_bsize = ctx->clone_data.sb->s_blocksize_bits;

        p = nfs_devname(dentry, buffer, 4096);
        if (IS_ERR(p)) {
                nfs_errorf(fc, "NFS: Couldn't determine submount pathname");
                ret = PTR_ERR(p);
        } else {
                ret = vfs_parse_fs_string(fc, "source", p, buffer + 4096 - p);
                if (!ret)
                        ret = vfs_get_tree(fc);
        }
        kfree(buffer);
        return ret;
}
EXPORT_SYMBOL_GPL(nfs_do_submount);

int nfs_submount(struct fs_context *fc, struct nfs_server *server)
{
        struct nfs_fs_context *ctx = nfs_fc2context(fc);
        struct dentry *dentry = ctx->clone_data.dentry;
        struct dentry *parent = dget_parent(dentry);
        int err;

        /* Look it up again to get its attributes */
        err = server->nfs_client->rpc_ops->lookup(d_inode(parent), dentry,
                                                  ctx->mntfh, ctx->clone_data.fattr,
                                                  NULL);
        dput(parent);
        if (err != 0)
                return err;

        ctx->selected_flavor = server->client->cl_auth->au_flavor;
        return nfs_do_submount(fc);
}
EXPORT_SYMBOL_GPL(nfs_submount);

static int param_set_nfs_timeout(const char *val, const struct kernel_param *kp)
{
        long num;
        int ret;

        if (!val)
                return -EINVAL;
        ret = kstrtol(val, 0, &num);
        if (ret)
                return -EINVAL;
        if (num > 0) {
                if (num >= INT_MAX / HZ)
                        num = INT_MAX;
                else
                        num *= HZ;
                *((int *)kp->arg) = num;
                if (!list_empty(&nfs_automount_list))
                        mod_delayed_work(system_wq, &nfs_automount_task, num);
        } else {
                *((int *)kp->arg) = -1*HZ;
                cancel_delayed_work(&nfs_automount_task);
        }
        return 0;
}

static int param_get_nfs_timeout(char *buffer, const struct kernel_param *kp)
{
        long num = *((int *)kp->arg);

        if (num > 0) {
                if (num >= INT_MAX - (HZ - 1))
                        num = INT_MAX / HZ;
                else
                        num = (num + (HZ - 1)) / HZ;
        } else
                num = -1;
        return scnprintf(buffer, PAGE_SIZE, "%li\n", num);
}

static const struct kernel_param_ops param_ops_nfs_timeout = {
        .set = param_set_nfs_timeout,
        .get = param_get_nfs_timeout,
};
#define param_check_nfs_timeout(name, p) __param_check(name, p, int)

module_param(nfs_mountpoint_expiry_timeout, nfs_timeout, 0644);
MODULE_PARM_DESC(nfs_mountpoint_expiry_timeout,
                "Set the NFS automounted mountpoint timeout value (seconds)."
                "Values <= 0 turn expiration off.");