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LSM: SafeSetID: refactor policy hash table

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parent_kuid and child_kuid are kuids, there is no reason to make them
uint64_t. (And anyway, in the kernel, the normal name for that would be
u64, not uint64_t.)

check_setuid_policy_hashtable_key() and
check_setuid_policy_hashtable_key_value() are basically the same thing,
merge them.

Also fix the comment that claimed that (1<<8)==128.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>
This commit is contained in:
Jann Horn 2019-04-10 09:55:34 -07:00 committed by Micah Morton
parent 7ef6b3062f
commit 1cd02a27a9
2 changed files with 37 additions and 44 deletions
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62
security/safesetid/lsm.c
View File

@ -14,67 +14,40 @@
#define pr_fmt(fmt) "SafeSetID: " fmt
#include <linux/hashtable.h>
#include <linux/lsm_hooks.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/sched/task_stack.h>
#include <linux/security.h>
#include "lsm.h"
/* Flag indicating whether initialization completed */
int safesetid_initialized;
#define NUM_BITS 8 /* 128 buckets in hash table */
#define NUM_BITS 8 /* 256 buckets in hash table */
static DEFINE_HASHTABLE(safesetid_whitelist_hashtable, NUM_BITS);
/*
* Hash table entry to store safesetid policy signifying that 'parent' user
* can setid to 'child' user.
*/
struct entry {
struct hlist_node next;
struct hlist_node dlist; /* for deletion cleanup */
uint64_t parent_kuid;
uint64_t child_kuid;
};
static DEFINE_SPINLOCK(safesetid_whitelist_hashtable_spinlock);
static bool check_setuid_policy_hashtable_key(kuid_t parent)
static enum sid_policy_type setuid_policy_lookup(kuid_t src, kuid_t dst)
{
struct entry *entry;
enum sid_policy_type result = SIDPOL_DEFAULT;
rcu_read_lock();
hash_for_each_possible_rcu(safesetid_whitelist_hashtable,
entry, next, __kuid_val(parent)) {
if (entry->parent_kuid == __kuid_val(parent)) {
entry, next, __kuid_val(src)) {
if (!uid_eq(entry->src_uid, src))
continue;
if (uid_eq(entry->dst_uid, dst)) {
rcu_read_unlock();
return true;
return SIDPOL_ALLOWED;
}
result = SIDPOL_CONSTRAINED;
}
rcu_read_unlock();
return false;
}
static bool check_setuid_policy_hashtable_key_value(kuid_t parent,
kuid_t child)
{
struct entry *entry;
rcu_read_lock();
hash_for_each_possible_rcu(safesetid_whitelist_hashtable,
entry, next, __kuid_val(parent)) {
if (entry->parent_kuid == __kuid_val(parent) &&
entry->child_kuid == __kuid_val(child)) {
rcu_read_unlock();
return true;
}
}
rcu_read_unlock();
return false;
return result;
}
static int safesetid_security_capable(const struct cred *cred,
@ -83,7 +56,7 @@ static int safesetid_security_capable(const struct cred *cred,
unsigned int opts)
{
if (cap == CAP_SETUID &&
check_setuid_policy_hashtable_key(cred->uid)) {
setuid_policy_lookup(cred->uid, INVALID_UID) != SIDPOL_DEFAULT) {
if (!(opts & CAP_OPT_INSETID)) {
/*
* Deny if we're not in a set*uid() syscall to avoid
@ -116,7 +89,8 @@ static bool uid_permitted_for_cred(const struct cred *old, kuid_t new_uid)
* Transitions to new UIDs require a check against the policy of the old
* RUID.
*/
permitted = check_setuid_policy_hashtable_key_value(old->uid, new_uid);
permitted =
setuid_policy_lookup(old->uid, new_uid) != SIDPOL_CONSTRAINED;
if (!permitted) {
pr_warn("UID transition ((%d,%d,%d) -> %d) blocked\n",
__kuid_val(old->uid), __kuid_val(old->euid),
@ -136,7 +110,7 @@ static int safesetid_task_fix_setuid(struct cred *new,
{
/* Do nothing if there are no setuid restrictions for our old RUID. */
if (!check_setuid_policy_hashtable_key(old->uid))
if (setuid_policy_lookup(old->uid, INVALID_UID) == SIDPOL_DEFAULT)
return 0;
if (uid_permitted_for_cred(old, new->uid) &&
@ -159,14 +133,14 @@ int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child)
struct entry *new;
/* Return if entry already exists */
if (check_setuid_policy_hashtable_key_value(parent, child))
if (setuid_policy_lookup(parent, child) == SIDPOL_ALLOWED)
return 0;
new = kzalloc(sizeof(struct entry), GFP_KERNEL);
if (!new)
return -ENOMEM;
new->parent_kuid = __kuid_val(parent);
new->child_kuid = __kuid_val(child);
new->src_uid = parent;
new->dst_uid = child;
spin_lock(&safesetid_whitelist_hashtable_spinlock);
hash_add_rcu(safesetid_whitelist_hashtable,
&new->next,

19
security/safesetid/lsm.h
View File

@ -15,6 +15,8 @@
#define _SAFESETID_H
#include <linux/types.h>
#include <linux/uidgid.h>
#include <linux/hashtable.h>
/* Flag indicating whether initialization completed */
extern int safesetid_initialized;
@ -25,6 +27,23 @@ enum safesetid_whitelist_file_write_type {
SAFESETID_WHITELIST_FLUSH, /* Flush whitelist policies. */
};
enum sid_policy_type {
SIDPOL_DEFAULT, /* source ID is unaffected by policy */
SIDPOL_CONSTRAINED, /* source ID is affected by policy */
SIDPOL_ALLOWED /* target ID explicitly allowed */
};
/*
* Hash table entry to store safesetid policy signifying that 'src_uid'
* can setid to 'dst_uid'.
*/
struct entry {
struct hlist_node next;
struct hlist_node dlist; /* for deletion cleanup */
kuid_t src_uid;
kuid_t dst_uid;
};
/* Add entry to safesetid whitelist to allow 'parent' to setid to 'child'. */
int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child);