linux-stable/fs/afs/security.c
Christian Brauner 549c729771
fs: make helpers idmap mount aware
Extend some inode methods with an additional user namespace argument. A
filesystem that is aware of idmapped mounts will receive the user
namespace the mount has been marked with. This can be used for
additional permission checking and also to enable filesystems to
translate between uids and gids if they need to. We have implemented all
relevant helpers in earlier patches.

As requested we simply extend the exisiting inode method instead of
introducing new ones. This is a little more code churn but it's mostly
mechanical and doesnt't leave us with additional inode methods.

Link: https://lore.kernel.org/r/20210121131959.646623-25-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:20 +01:00

488 lines
12 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/* AFS security handling
*
* Copyright (C) 2007, 2017 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#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_net(&key_type_rxrpc, cell->anonymous_key->description,
cell->net->net, 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;
}
}
/*
* Get a key when pathwalk is in rcuwalk mode.
*/
struct key *afs_request_key_rcu(struct afs_cell *cell)
{
struct key *key;
_enter("{%x}", key_serial(cell->anonymous_key));
_debug("key %s", cell->anonymous_key->description);
key = request_key_net_rcu(&key_type_rxrpc,
cell->anonymous_key->description,
cell->net->net);
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);
spin_unlock(&vnode->lock);
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_status_cb *scb)
{
struct afs_permits *permits, *xpermits, *replacement, *zap, *new = NULL;
afs_access_t caller_access = scb->status.caller_access;
size_t size = 0;
bool changed = false;
int i, j;
_enter("{%llx:%llu},%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 (afs_cb_is_broken(cb_break, vnode)) {
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 (afs_cb_is_broken(cb_break, vnode))
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);
rcu_read_lock();
spin_lock(&vnode->lock);
zap = rcu_access_pointer(vnode->permit_cache);
if (!afs_cb_is_broken(cb_break, vnode) && zap == permits)
rcu_assign_pointer(vnode->permit_cache, replacement);
else
zap = replacement;
spin_unlock(&vnode->lock);
rcu_read_unlock();
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;
}
static bool afs_check_permit_rcu(struct afs_vnode *vnode, struct key *key,
afs_access_t *_access)
{
const struct afs_permits *permits;
int i;
_enter("{%llx:%llu},%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) {
*_access = vnode->status.anon_access;
_leave(" = t [anon %x]", *_access);
return true;
}
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;
_leave(" = %u [perm %x]", !permits->invalidated, *_access);
return !permits->invalidated;
}
}
_leave(" = f");
return false;
}
/*
* 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("{%llx:%llu},%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, _access);
if (ret < 0) {
*_access = 0;
_leave(" = %d", ret);
return ret;
}
}
_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 user_namespace *mnt_userns, struct inode *inode,
int mask)
{
struct afs_vnode *vnode = AFS_FS_I(inode);
afs_access_t access;
struct key *key;
int ret = 0;
_enter("{{%llx:%llu},%lx},%x,",
vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
if (mask & MAY_NOT_BLOCK) {
key = afs_request_key_rcu(vnode->volume->cell);
if (IS_ERR(key))
return -ECHILD;
ret = -ECHILD;
if (!afs_check_validity(vnode) ||
!afs_check_permit_rcu(vnode, key, &access))
goto error;
} else {
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");
ret = 0;
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]));
}