/* AFS security handling
 *
 * Copyright (C) 2007 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 <keys/rxrpc-type.h>
#include "internal.h"

/*
 * 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 permits list
 */
void afs_zap_permits(struct rcu_head *rcu)
{
        struct afs_permits *permits =
                container_of(rcu, struct afs_permits, rcu);
        int loop;

        _enter("{%d}", permits->count);

        for (loop = permits->count - 1; loop >= 0; loop--)
                key_put(permits->permits[loop].key);
        kfree(permits);
}

/*
 * dispose of a permits list in which all the key pointers have been copied
 */
static void afs_dispose_of_permits(struct rcu_head *rcu)
{
        struct afs_permits *permits =
                container_of(rcu, struct afs_permits, rcu);

        _enter("{%d}", permits->count);

        kfree(permits);
}

/*
 * get the authorising vnode - this is the specified inode itself if it's a
 * directory or it's the parent directory if the specified inode is a file or
 * symlink
 * - the caller must release the ref on the inode
 */
static struct afs_vnode *afs_get_auth_inode(struct afs_vnode *vnode,
                                            struct key *key)
{
        struct afs_vnode *auth_vnode;
        struct inode *auth_inode;

        _enter("");

        if (S_ISDIR(vnode->vfs_inode.i_mode)) {
                auth_inode = igrab(&vnode->vfs_inode);
                ASSERT(auth_inode != NULL);
        } else {
                auth_inode = afs_iget(vnode->vfs_inode.i_sb, key,
                                      &vnode->status.parent, NULL, NULL);
                if (IS_ERR(auth_inode))
                        return ERR_CAST(auth_inode);
        }

        auth_vnode = AFS_FS_I(auth_inode);
        _leave(" = {%x}", auth_vnode->fid.vnode);
        return auth_vnode;
}

/*
 * clear the permit cache on a directory vnode
 */
void afs_clear_permits(struct afs_vnode *vnode)
{
        struct afs_permits *permits;

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

        mutex_lock(&vnode->permits_lock);
        permits = vnode->permits;
        rcu_assign_pointer(vnode->permits, NULL);
        mutex_unlock(&vnode->permits_lock);

        if (permits)
                call_rcu(&permits->rcu, afs_zap_permits);
        _leave("");
}

/*
 * add the result obtained for a vnode to its or its parent directory's cache
 * for the key used to access it
 */
void afs_cache_permit(struct afs_vnode *vnode, struct key *key, long acl_order)
{
        struct afs_permits *permits, *xpermits;
        struct afs_permit *permit;
        struct afs_vnode *auth_vnode;
        int count, loop;

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

        auth_vnode = afs_get_auth_inode(vnode, key);
        if (IS_ERR(auth_vnode)) {
                _leave(" [get error %ld]", PTR_ERR(auth_vnode));
                return;
        }

        mutex_lock(&auth_vnode->permits_lock);

        /* guard against a rename being detected whilst we waited for the
         * lock */
        if (memcmp(&auth_vnode->fid, &vnode->status.parent,
                   sizeof(struct afs_fid)) != 0) {
                _debug("renamed");
                goto out_unlock;
        }

        /* have to be careful as the directory's callback may be broken between
         * us receiving the status we're trying to cache and us getting the
         * lock to update the cache for the status */
        if (auth_vnode->acl_order - acl_order > 0) {
                _debug("ACL changed?");
                goto out_unlock;
        }

        /* always update the anonymous mask */
        _debug("anon access %x", vnode->status.anon_access);
        auth_vnode->status.anon_access = vnode->status.anon_access;
        if (key == vnode->volume->cell->anonymous_key)
                goto out_unlock;

        xpermits = auth_vnode->permits;
        count = 0;
        if (xpermits) {
                /* see if the permit is already in the list
                 * - if it is then we just amend the list
                 */
                count = xpermits->count;
                permit = xpermits->permits;
                for (loop = count; loop > 0; loop--) {
                        if (permit->key == key) {
                                permit->access_mask =
                                        vnode->status.caller_access;
                                goto out_unlock;
                        }
                        permit++;
                }
        }

        permits = kmalloc(sizeof(*permits) + sizeof(*permit) * (count + 1),
                          GFP_NOFS);
        if (!permits)
                goto out_unlock;

        if (xpermits)
                memcpy(permits->permits, xpermits->permits,
                        count * sizeof(struct afs_permit));

        _debug("key %x access %x",
               key_serial(key), vnode->status.caller_access);
        permits->permits[count].access_mask = vnode->status.caller_access;
        permits->permits[count].key = key_get(key);
        permits->count = count + 1;

        rcu_assign_pointer(auth_vnode->permits, permits);
        if (xpermits)
                call_rcu(&xpermits->rcu, afs_dispose_of_permits);

out_unlock:
        mutex_unlock(&auth_vnode->permits_lock);
        iput(&auth_vnode->vfs_inode);
        _leave("");
}

/*
 * 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
 */
static int afs_check_permit(struct afs_vnode *vnode, struct key *key,
                            afs_access_t *_access)
{
        struct afs_permits *permits;
        struct afs_permit *permit;
        struct afs_vnode *auth_vnode;
        bool valid;
        int loop, ret;

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

        auth_vnode = afs_get_auth_inode(vnode, key);
        if (IS_ERR(auth_vnode)) {
                *_access = 0;
                _leave(" = %ld", PTR_ERR(auth_vnode));
                return PTR_ERR(auth_vnode);
        }

        ASSERT(S_ISDIR(auth_vnode->vfs_inode.i_mode));

        /* check the permits to see if we've got one yet */
        if (key == auth_vnode->volume->cell->anonymous_key) {
                _debug("anon");
                *_access = auth_vnode->status.anon_access;
                valid = true;
        } else {
                valid = false;
                rcu_read_lock();
                permits = rcu_dereference(auth_vnode->permits);
                if (permits) {
                        permit = permits->permits;
                        for (loop = permits->count; loop > 0; loop--) {
                                if (permit->key == key) {
                                        _debug("found in cache");
                                        *_access = permit->access_mask;
                                        valid = true;
                                        break;
                                }
                                permit++;
                        }
                }
                rcu_read_unlock();
        }

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

                set_bit(AFS_VNODE_CB_BROKEN, &vnode->flags);
                ret = afs_vnode_fetch_status(vnode, auth_vnode, key);
                if (ret < 0) {
                        iput(&auth_vnode->vfs_inode);
                        *_access = 0;
                        _leave(" = %d", ret);
                        return ret;
                }
                *_access = vnode->status.caller_access;
        }

        iput(&auth_vnode->vfs_inode);
        _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);
        }

        /* if the promise has expired, we need to check the server again */
        if (!vnode->cb_promised) {
                _debug("not promised");
                ret = afs_vnode_fetch_status(vnode, NULL, key);
                if (ret < 0)
                        goto error;
                _debug("new promise [fl=%lx]", vnode->flags);
        }

        /* 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) {
                        if (!(access & AFS_ACE_LOOKUP))
                                goto permission_denied;
                } else if (mask & MAY_READ) {
                        if (!(access & AFS_ACE_READ))
                                goto permission_denied;
                } else if (mask & MAY_WRITE) {
                        if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
                                        AFS_ACE_INSERT | /* create, mkdir, symlink, rename to */
                                        AFS_ACE_WRITE))) /* chmod */
                                goto permission_denied;
                } else {
                        BUG();
                }
        } else {
                if (!(access & AFS_ACE_LOOKUP))
                        goto permission_denied;
                if (mask & (MAY_EXEC | MAY_READ)) {
                        if (!(access & AFS_ACE_READ))
                                goto permission_denied;
                } else if (mask & MAY_WRITE) {
                        if (!(access & AFS_ACE_WRITE))
                                goto permission_denied;
                }
        }

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

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