2
0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-23 12:43:55 +08:00
linux-next/fs/afs/security.c
David Howells d2ddc776a4 afs: Overhaul volume and server record caching and fileserver rotation
The current code assumes that volumes and servers are per-cell and are
never shared, but this is not enforced, and, indeed, public cells do exist
that are aliases of each other.  Further, an organisation can, say, set up
a public cell and a private cell with overlapping, but not identical, sets
of servers.  The difference is purely in the database attached to the VL
servers.

The current code will malfunction if it sees a server in two cells as it
assumes global address -> server record mappings and that each server is in
just one cell.

Further, each server may have multiple addresses - and may have addresses
of different families (IPv4 and IPv6, say).

To this end, the following structural changes are made:

 (1) Server record management is overhauled:

     (a) Server records are made independent of cell.  The namespace keeps
     	 track of them, volume records have lists of them and each vnode
     	 has a server on which its callback interest currently resides.

     (b) The cell record no longer keeps a list of servers known to be in
     	 that cell.

     (c) The server records are now kept in a flat list because there's no
     	 single address to sort on.

     (d) Server records are now keyed by their UUID within the namespace.

     (e) The addresses for a server are obtained with the VL.GetAddrsU
     	 rather than with VL.GetEntryByName, using the server's UUID as a
     	 parameter.

     (f) Cached server records are garbage collected after a period of
     	 non-use and are counted out of existence before purging is allowed
     	 to complete.  This protects the work functions against rmmod.

     (g) The servers list is now in /proc/fs/afs/servers.

 (2) Volume record management is overhauled:

     (a) An RCU-replaceable server list is introduced.  This tracks both
     	 servers and their coresponding callback interests.

     (b) The superblock is now keyed on cell record and numeric volume ID.

     (c) The volume record is now tied to the superblock which mounts it,
     	 and is activated when mounted and deactivated when unmounted.
     	 This makes it easier to handle the cache cookie without causing a
     	 double-use in fscache.

     (d) The volume record is loaded from the VLDB using VL.GetEntryByNameU
     	 to get the server UUID list.

     (e) The volume name is updated if it is seen to have changed when the
     	 volume is updated (the update is keyed on the volume ID).

 (3) The vlocation record is got rid of and VLDB records are no longer
     cached.  Sufficient information is stored in the volume record, though
     an update to a volume record is now no longer shared between related
     volumes (volumes come in bundles of three: R/W, R/O and backup).

and the following procedural changes are made:

 (1) The fileserver cursor introduced previously is now fleshed out and
     used to iterate over fileservers and their addresses.

 (2) Volume status is checked during iteration, and the server list is
     replaced if a change is detected.

 (3) Server status is checked during iteration, and the address list is
     replaced if a change is detected.

 (4) The abort code is saved into the address list cursor and -ECONNABORTED
     returned in afs_make_call() if a remote abort happened rather than
     translating the abort into an error message.  This allows actions to
     be taken depending on the abort code more easily.

     (a) If a VMOVED abort is seen then this is handled by rechecking the
     	 volume and restarting the iteration.

     (b) If a VBUSY, VRESTARTING or VSALVAGING abort is seen then this is
         handled by sleeping for a short period and retrying and/or trying
         other servers that might serve that volume.  A message is also
         displayed once until the condition has cleared.

     (c) If a VOFFLINE abort is seen, then this is handled as VBUSY for the
     	 moment.

     (d) If a VNOVOL abort is seen, the volume is rechecked in the VLDB to
     	 see if it has been deleted; if not, the fileserver is probably
     	 indicating that the volume couldn't be attached and needs
     	 salvaging.

     (e) If statfs() sees one of these aborts, it does not sleep, but
     	 rather returns an error, so as not to block the umount program.

 (5) The fileserver iteration functions in vnode.c are now merged into
     their callers and more heavily macroised around the cursor.  vnode.c
     is removed.

 (6) Operations on a particular vnode are serialised on that vnode because
     the server will lock that vnode whilst it operates on it, so a second
     op sent will just have to wait.

 (7) Fileservers are probed with FS.GetCapabilities before being used.
     This is where service upgrade will be done.

 (8) A callback interest on a fileserver is set up before an FS operation
     is performed and passed through to afs_make_call() so that it can be
     set on the vnode if the operation returns a callback.  The callback
     interest is passed through to afs_iget() also so that it can be set
     there too.

In general, record updating is done on an as-needed basis when we try to
access servers, volumes or vnodes rather than offloading it to work items
and special threads.

Notes:

 (1) Pre AFS-3.4 servers are no longer supported, though this can be added
     back if necessary (AFS-3.4 was released in 1998).

 (2) VBUSY is retried forever for the moment at intervals of 1s.

 (3) /proc/fs/afs/<cell>/servers no longer exists.

Signed-off-by: David Howells <dhowells@redhat.com>
2017-11-13 15:38:19 +00:00

430 lines
10 KiB
C

/* 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, *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 != (vnode->cb_break +
vnode->cb_interest->server->cb_s_break)) {
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 != (vnode->cb_break + vnode->cb_interest->server->cb_s_break)) {
rcu_read_unlock();
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)) {
rcu_read_unlock();
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)
return;
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);
afs_put_permits(permits);
/* 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);
if (cb_break != (vnode->cb_break + vnode->cb_interest->server->cb_s_break) ||
permits != rcu_access_pointer(vnode->permit_cache))
goto someone_else_changed_it_unlock;
rcu_assign_pointer(vnode->permit_cache, replacement);
spin_unlock(&vnode->lock);
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.
*/
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
*/
static 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));
permits = vnode->permit_cache;
/* 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);
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) {
if (!(access & AFS_ACE_LOOKUP))
goto permission_denied;
} else if (mask & MAY_READ) {
if (!(access & AFS_ACE_LOOKUP))
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 */
goto permission_denied;
} else {
BUG();
}
} 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]));
}