linux/security/selinux/ss/hashtab.h
Stephen Smalley c7c556f1e8 selinux: refactor changing booleans
Refactor the logic for changing SELinux policy booleans in a similar
manner to the refactoring of policy load, thereby reducing the
size of the critical section when the policy write-lock is held
and making it easier to convert the policy rwlock to RCU in the
future.  Instead of directly modifying the policydb in place, modify
a copy and then swap it into place through a single pointer update.
Only fully copy the portions of the policydb that are affected by
boolean changes to avoid the full cost of a deep policydb copy.
Introduce another level of indirection for the sidtab since changing
booleans does not require updating the sidtab, unlike policy load.
While we are here, create a common helper for notifying
other kernel components and userspace of a policy change and call it
from both security_set_bools() and selinux_policy_commit().

Based on an old (2004) patch by Kaigai Kohei [1] to convert the policy
rwlock to RCU that was deferred at the time since it did not
significantly improve performance and introduced complexity. Peter
Enderborg later submitted a patch series to convert to RCU [2] that
would have made changing booleans a much more expensive operation
by requiring a full policydb_write();policydb_read(); sequence to
deep copy the entire policydb and also had concerns regarding
atomic allocations.

This change is now simplified by the earlier work to encapsulate
policy state in the selinux_policy struct and to refactor
policy load.  After this change, the last major obstacle to
converting the policy rwlock to RCU is likely the sidtab live
convert support.

[1] https://lore.kernel.org/selinux/6e2f9128-e191-ebb3-0e87-74bfccb0767f@tycho.nsa.gov/
[2] https://lore.kernel.org/selinux/20180530141104.28569-1-peter.enderborg@sony.com/

Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
2020-08-17 21:00:33 -04:00

149 lines
3.6 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
/*
* A hash table (hashtab) maintains associations between
* key values and datum values. The type of the key values
* and the type of the datum values is arbitrary. The
* functions for hash computation and key comparison are
* provided by the creator of the table.
*
* Author : Stephen Smalley, <sds@tycho.nsa.gov>
*/
#ifndef _SS_HASHTAB_H_
#define _SS_HASHTAB_H_
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/sched.h>
#define HASHTAB_MAX_NODES U32_MAX
struct hashtab_key_params {
u32 (*hash)(const void *key); /* hash function */
int (*cmp)(const void *key1, const void *key2);
/* key comparison function */
};
struct hashtab_node {
void *key;
void *datum;
struct hashtab_node *next;
};
struct hashtab {
struct hashtab_node **htable; /* hash table */
u32 size; /* number of slots in hash table */
u32 nel; /* number of elements in hash table */
};
struct hashtab_info {
u32 slots_used;
u32 max_chain_len;
};
/*
* Initializes a new hash table with the specified characteristics.
*
* Returns -ENOMEM if insufficient space is available or 0 otherwise.
*/
int hashtab_init(struct hashtab *h, u32 nel_hint);
int __hashtab_insert(struct hashtab *h, struct hashtab_node **dst,
void *key, void *datum);
/*
* Inserts the specified (key, datum) pair into the specified hash table.
*
* Returns -ENOMEM on memory allocation error,
* -EEXIST if there is already an entry with the same key,
* -EINVAL for general errors or
0 otherwise.
*/
static inline int hashtab_insert(struct hashtab *h, void *key, void *datum,
struct hashtab_key_params key_params)
{
u32 hvalue;
struct hashtab_node *prev, *cur;
cond_resched();
if (!h->size || h->nel == HASHTAB_MAX_NODES)
return -EINVAL;
hvalue = key_params.hash(key) & (h->size - 1);
prev = NULL;
cur = h->htable[hvalue];
while (cur) {
int cmp = key_params.cmp(key, cur->key);
if (cmp == 0)
return -EEXIST;
if (cmp < 0)
break;
prev = cur;
cur = cur->next;
}
return __hashtab_insert(h, prev ? &prev->next : &h->htable[hvalue],
key, datum);
}
/*
* Searches for the entry with the specified key in the hash table.
*
* Returns NULL if no entry has the specified key or
* the datum of the entry otherwise.
*/
static inline void *hashtab_search(struct hashtab *h, const void *key,
struct hashtab_key_params key_params)
{
u32 hvalue;
struct hashtab_node *cur;
if (!h->size)
return NULL;
hvalue = key_params.hash(key) & (h->size - 1);
cur = h->htable[hvalue];
while (cur) {
int cmp = key_params.cmp(key, cur->key);
if (cmp == 0)
return cur->datum;
if (cmp < 0)
break;
cur = cur->next;
}
return NULL;
}
/*
* Destroys the specified hash table.
*/
void hashtab_destroy(struct hashtab *h);
/*
* Applies the specified apply function to (key,datum,args)
* for each entry in the specified hash table.
*
* The order in which the function is applied to the entries
* is dependent upon the internal structure of the hash table.
*
* If apply returns a non-zero status, then hashtab_map will cease
* iterating through the hash table and will propagate the error
* return to its caller.
*/
int hashtab_map(struct hashtab *h,
int (*apply)(void *k, void *d, void *args),
void *args);
int hashtab_duplicate(struct hashtab *new, struct hashtab *orig,
int (*copy)(struct hashtab_node *new,
struct hashtab_node *orig, void *args),
int (*destroy)(void *k, void *d, void *args),
void *args);
/* Fill info with some hash table statistics */
void hashtab_stat(struct hashtab *h, struct hashtab_info *info);
#endif /* _SS_HASHTAB_H */