/* AFS security handling
 *
 * Copyright (C) 2007, 2017 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/init.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/ctype.h>
#include <linux/sched.h>
#include <linux/hashtable.h>
#include <keys/rxrpc-type.h>
#include "internal.h"

static DEFINE_HASHTABLE(afs_permits_cache, 10);
static DEFINE_SPINLOCK(afs_permits_lock);

/*
 * get a key
 */
struct key *afs_request_key(struct afs_cell *cell)
{
        struct key *key;

        _enter("{%x}", key_serial(cell->anonymous_key));

        _debug("key %s", cell->anonymous_key->description);
        key = request_key(&key_type_rxrpc, cell->anonymous_key->description,
                          NULL);
        if (IS_ERR(key)) {
                if (PTR_ERR(key) != -ENOKEY) {
                        _leave(" = %ld", PTR_ERR(key));
                        return key;
                }

                /* act as anonymous user */
                _leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
                return key_get(cell->anonymous_key);
        } else {
                /* act as authorised user */
                _leave(" = {%x} [auth]", key_serial(key));
                return key;
        }
}

/*
 * Dispose of a list of permits.
 */
static void afs_permits_rcu(struct rcu_head *rcu)
{
        struct afs_permits *permits =
                container_of(rcu, struct afs_permits, rcu);
        int i;

        for (i = 0; i < permits->nr_permits; i++)
                key_put(permits->permits[i].key);
        kfree(permits);
}

/*
 * Discard a permission cache.
 */
void afs_put_permits(struct afs_permits *permits)
{
        if (permits && refcount_dec_and_test(&permits->usage)) {
                spin_lock(&afs_permits_lock);
                hash_del_rcu(&permits->hash_node);
                spin_unlock(&afs_permits_lock);
                call_rcu(&permits->rcu, afs_permits_rcu);
        }
}

/*
 * Clear a permit cache on callback break.
 */
void afs_clear_permits(struct afs_vnode *vnode)
{
        struct afs_permits *permits;

        spin_lock(&vnode->lock);
        permits = rcu_dereference_protected(vnode->permit_cache,
                                            lockdep_is_held(&vnode->lock));
        RCU_INIT_POINTER(vnode->permit_cache, NULL);
        vnode->cb_break++;
        spin_unlock(&vnode->lock);

        if (permits)
                afs_put_permits(permits);
}

/*
 * Hash a list of permits.  Use simple addition to make it easy to add an extra
 * one at an as-yet indeterminate position in the list.
 */
static void afs_hash_permits(struct afs_permits *permits)
{
        unsigned long h = permits->nr_permits;
        int i;

        for (i = 0; i < permits->nr_permits; i++) {
                h += (unsigned long)permits->permits[i].key / sizeof(void *);
                h += permits->permits[i].access;
        }

        permits->h = h;
}

/*
 * Cache the CallerAccess result obtained from doing a fileserver operation
 * that returned a vnode status for a particular key.  If a callback break
 * occurs whilst the operation was in progress then we have to ditch the cache
 * as the ACL *may* have changed.
 */
void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
                      unsigned int cb_break)
{
        struct afs_permits *permits, *xpermits, *replacement, *zap, *new = NULL;
        afs_access_t caller_access = READ_ONCE(vnode->status.caller_access);
        size_t size = 0;
        bool changed = false;
        int i, j;

        _enter("{%x:%u},%x,%x",
               vnode->fid.vid, vnode->fid.vnode, key_serial(key), caller_access);

        rcu_read_lock();

        /* Check for the common case first: We got back the same access as last
         * time we tried and already have it recorded.
         */
        permits = rcu_dereference(vnode->permit_cache);
        if (permits) {
                if (!permits->invalidated) {
                        for (i = 0; i < permits->nr_permits; i++) {
                                if (permits->permits[i].key < key)
                                        continue;
                                if (permits->permits[i].key > key)
                                        break;
                                if (permits->permits[i].access != caller_access) {
                                        changed = true;
                                        break;
                                }

                                if (cb_break != afs_cb_break_sum(vnode, vnode->cb_interest)) {
                                        changed = true;
                                        break;
                                }

                                /* The cache is still good. */
                                rcu_read_unlock();
                                return;
                        }
                }

                changed |= permits->invalidated;
                size = permits->nr_permits;

                /* If this set of permits is now wrong, clear the permits
                 * pointer so that no one tries to use the stale information.
                 */
                if (changed) {
                        spin_lock(&vnode->lock);
                        if (permits != rcu_access_pointer(vnode->permit_cache))
                                goto someone_else_changed_it_unlock;
                        RCU_INIT_POINTER(vnode->permit_cache, NULL);
                        spin_unlock(&vnode->lock);

                        afs_put_permits(permits);
                        permits = NULL;
                        size = 0;
                }
        }

        if (cb_break != afs_cb_break_sum(vnode, vnode->cb_interest))
                goto someone_else_changed_it;

        /* We need a ref on any permits list we want to copy as we'll have to
         * drop the lock to do memory allocation.
         */
        if (permits && !refcount_inc_not_zero(&permits->usage))
                goto someone_else_changed_it;

        rcu_read_unlock();

        /* Speculatively create a new list with the revised permission set.  We
         * discard this if we find an extant match already in the hash, but
         * it's easier to compare with memcmp this way.
         *
         * We fill in the key pointers at this time, but we don't get the refs
         * yet.
         */
        size++;
        new = kzalloc(sizeof(struct afs_permits) +
                      sizeof(struct afs_permit) * size, GFP_NOFS);
        if (!new)
                goto out_put;

        refcount_set(&new->usage, 1);
        new->nr_permits = size;
        i = j = 0;
        if (permits) {
                for (i = 0; i < permits->nr_permits; i++) {
                        if (j == i && permits->permits[i].key > key) {
                                new->permits[j].key = key;
                                new->permits[j].access = caller_access;
                                j++;
                        }
                        new->permits[j].key = permits->permits[i].key;
                        new->permits[j].access = permits->permits[i].access;
                        j++;
                }
        }

        if (j == i) {
                new->permits[j].key = key;
                new->permits[j].access = caller_access;
        }

        afs_hash_permits(new);

        /* Now see if the permit list we want is actually already available */
        spin_lock(&afs_permits_lock);

        hash_for_each_possible(afs_permits_cache, xpermits, hash_node, new->h) {
                if (xpermits->h != new->h ||
                    xpermits->invalidated ||
                    xpermits->nr_permits != new->nr_permits ||
                    memcmp(xpermits->permits, new->permits,
                           new->nr_permits * sizeof(struct afs_permit)) != 0)
                        continue;

                if (refcount_inc_not_zero(&xpermits->usage)) {
                        replacement = xpermits;
                        goto found;
                }

                break;
        }

        for (i = 0; i < new->nr_permits; i++)
                key_get(new->permits[i].key);
        hash_add_rcu(afs_permits_cache, &new->hash_node, new->h);
        replacement = new;
        new = NULL;

found:
        spin_unlock(&afs_permits_lock);

        kfree(new);

        spin_lock(&vnode->lock);
        zap = rcu_access_pointer(vnode->permit_cache);
        if (cb_break == afs_cb_break_sum(vnode, vnode->cb_interest) &&
            zap == permits)
                rcu_assign_pointer(vnode->permit_cache, replacement);
        else
                zap = replacement;
        spin_unlock(&vnode->lock);
        afs_put_permits(zap);
out_put:
        afs_put_permits(permits);
        return;

someone_else_changed_it_unlock:
        spin_unlock(&vnode->lock);
someone_else_changed_it:
        /* Someone else changed the cache under us - don't recheck at this
         * time.
         */
        rcu_read_unlock();
        return;
}

/*
 * check with the fileserver to see if the directory or parent directory is
 * permitted to be accessed with this authorisation, and if so, what access it
 * is granted
 */
int afs_check_permit(struct afs_vnode *vnode, struct key *key,
                     afs_access_t *_access)
{
        struct afs_permits *permits;
        bool valid = false;
        int i, ret;

        _enter("{%x:%u},%x",
               vnode->fid.vid, vnode->fid.vnode, key_serial(key));

        /* check the permits to see if we've got one yet */
        if (key == vnode->volume->cell->anonymous_key) {
                _debug("anon");
                *_access = vnode->status.anon_access;
                valid = true;
        } else {
                rcu_read_lock();
                permits = rcu_dereference(vnode->permit_cache);
                if (permits) {
                        for (i = 0; i < permits->nr_permits; i++) {
                                if (permits->permits[i].key < key)
                                        continue;
                                if (permits->permits[i].key > key)
                                        break;

                                *_access = permits->permits[i].access;
                                valid = !permits->invalidated;
                                break;
                        }
                }
                rcu_read_unlock();
        }

        if (!valid) {
                /* Check the status on the file we're actually interested in
                 * (the post-processing will cache the result).
                 */
                _debug("no valid permit");

                ret = afs_fetch_status(vnode, key, false);
                if (ret < 0) {
                        *_access = 0;
                        _leave(" = %d", ret);
                        return ret;
                }
                *_access = vnode->status.caller_access;
        }

        _leave(" = 0 [access %x]", *_access);
        return 0;
}

/*
 * check the permissions on an AFS file
 * - AFS ACLs are attached to directories only, and a file is controlled by its
 *   parent directory's ACL
 */
int afs_permission(struct inode *inode, int mask)
{
        struct afs_vnode *vnode = AFS_FS_I(inode);
        afs_access_t uninitialized_var(access);
        struct key *key;
        int ret;

        if (mask & MAY_NOT_BLOCK)
                return -ECHILD;

        _enter("{{%x:%u},%lx},%x,",
               vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);

        key = afs_request_key(vnode->volume->cell);
        if (IS_ERR(key)) {
                _leave(" = %ld [key]", PTR_ERR(key));
                return PTR_ERR(key);
        }

        ret = afs_validate(vnode, key);
        if (ret < 0)
                goto error;

        /* check the permits to see if we've got one yet */
        ret = afs_check_permit(vnode, key, &access);
        if (ret < 0)
                goto error;

        /* interpret the access mask */
        _debug("REQ %x ACC %x on %s",
               mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");

        if (S_ISDIR(inode->i_mode)) {
                if (mask & (MAY_EXEC | MAY_READ | MAY_CHDIR)) {
                        if (!(access & AFS_ACE_LOOKUP))
                                goto permission_denied;
                }
                if (mask & MAY_WRITE) {
                        if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
                                        AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
                                goto permission_denied;
                }
        } else {
                if (!(access & AFS_ACE_LOOKUP))
                        goto permission_denied;
                if ((mask & MAY_EXEC) && !(inode->i_mode & S_IXUSR))
                        goto permission_denied;
                if (mask & (MAY_EXEC | MAY_READ)) {
                        if (!(access & AFS_ACE_READ))
                                goto permission_denied;
                        if (!(inode->i_mode & S_IRUSR))
                                goto permission_denied;
                } else if (mask & MAY_WRITE) {
                        if (!(access & AFS_ACE_WRITE))
                                goto permission_denied;
                        if (!(inode->i_mode & S_IWUSR))
                                goto permission_denied;
                }
        }

        key_put(key);
        _leave(" = %d", ret);
        return ret;

permission_denied:
        ret = -EACCES;
error:
        key_put(key);
        _leave(" = %d", ret);
        return ret;
}

void __exit afs_clean_up_permit_cache(void)
{
        int i;

        for (i = 0; i < HASH_SIZE(afs_permits_cache); i++)
                WARN_ON_ONCE(!hlist_empty(&afs_permits_cache[i]));

}