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Subject[PATCH 9/9] Protect SELinux initialized state with pmalloc
Date
SELinux is one of the primary targets, when a system running it comes
under attack.

The reason is that, even if an attacker ishould manage to gain root,
SELinux will still prevent most desirable actions.

Even in a fully locked down system, SELinux still presents a vulnerability
that is often exploited, because it is very simple to attack, once
kernel address layout randomization has been defeated and the attacker
has gained capability of writing to kernelunprotected data.

In various places, SELinux relies on an "initialized" internal state
variable, to decide if the policy is loaded and tests should be
performed. Needless to say, it's in the interest of hte attacker to turn
it off and pretend that the policyDB is still uninitialized.

Even if recent patches move the "initialized" state inside a structure,
it is still vulnerable.

This patch seeks to protect it, using it as demo for the pmalloc API,
which is meant to provide additional protection to data which is likely
to not be changed very often, if ever (after a transient).

The patch is probably in need of rework, to make it fit better with the
new SELinux internal data structures, however it shows how to deny an
easy target to the attacker.

In case the kernel is compiled with JOP safeguards, then it becomes far
harder for the attacker to jump into the middle of the function which
calls pmalloc_rare_write, to alter the state.

Signed-off-by: Igor Stoppa <igor.stoppa@huawei.com>
---
security/selinux/hooks.c | 12 ++++-----
security/selinux/include/security.h | 2 +-
security/selinux/ss/services.c | 51 +++++++++++++++++++++++--------------
3 files changed, 39 insertions(+), 26 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 4cafe6a19167..6049f80115bc 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -285,7 +285,7 @@ static int __inode_security_revalidate(struct inode *inode,

might_sleep_if(may_sleep);

- if (selinux_state.initialized &&
+ if (*ss_initialized_ptr &&
isec->initialized != LABEL_INITIALIZED) {
if (!may_sleep)
return -ECHILD;
@@ -612,7 +612,7 @@ static int selinux_get_mnt_opts(const struct super_block *sb,
if (!(sbsec->flags & SE_SBINITIALIZED))
return -EINVAL;

- if (!selinux_state.initialized)
+ if (!*ss_initialized_ptr)
return -EINVAL;

/* make sure we always check enough bits to cover the mask */
@@ -735,7 +735,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,

mutex_lock(&sbsec->lock);

- if (!selinux_state.initialized) {
+ if (!*ss_initialized_ptr) {
if (!num_opts) {
/* Defer initialization until selinux_complete_init,
after the initial policy is loaded and the security
@@ -1022,7 +1022,7 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
* if the parent was able to be mounted it clearly had no special lsm
* mount options. thus we can safely deal with this superblock later
*/
- if (!selinux_state.initialized)
+ if (!*ss_initialized_ptr)
return 0;

/*
@@ -3040,7 +3040,7 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
isec->initialized = LABEL_INITIALIZED;
}

- if (!selinux_state.initialized || !(sbsec->flags & SBLABEL_MNT))
+ if (!*ss_initialized_ptr || !(sbsec->flags & SBLABEL_MNT))
return -EOPNOTSUPP;

if (name)
@@ -7253,7 +7253,7 @@ static void selinux_nf_ip_exit(void)
#ifdef CONFIG_SECURITY_SELINUX_DISABLE
int selinux_disable(struct selinux_state *state)
{
- if (state->initialized) {
+ if (*ss_initialized_ptr) {
/* Not permitted after initial policy load. */
return -EINVAL;
}
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index 23e762d529fa..ec7debb143be 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -96,13 +96,13 @@ extern char *selinux_policycap_names[__POLICYDB_CAPABILITY_MAX];
struct selinux_avc;
struct selinux_ss;

+extern bool *ss_initialized_ptr;
struct selinux_state {
bool disabled;
#ifdef CONFIG_SECURITY_SELINUX_DEVELOP
bool enforcing;
#endif
bool checkreqprot;
- bool initialized;
bool policycap[__POLICYDB_CAPABILITY_MAX];
struct selinux_avc *avc;
struct selinux_ss *ss;
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 8057e19dc15f..c09ca6f9b269 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -52,6 +52,7 @@
#include <linux/selinux.h>
#include <linux/flex_array.h>
#include <linux/vmalloc.h>
+#include <linux/pmalloc.h>
#include <net/netlabel.h>

#include "flask.h"
@@ -80,10 +81,20 @@ char *selinux_policycap_names[__POLICYDB_CAPABILITY_MAX] = {
"nnp_nosuid_transition"
};

+bool *ss_initialized_ptr __ro_after_init;
+static struct pmalloc_pool *selinux_pool;
static struct selinux_ss selinux_ss;

void selinux_ss_init(struct selinux_ss **ss)
{
+ selinux_pool = pmalloc_create_pool(PMALLOC_RW);
+ if (unlikely(!selinux_pool))
+ panic("SELinux: unable to create pmalloc pool.");
+ ss_initialized_ptr = pmalloc(selinux_pool, sizeof(bool));
+ if (unlikely(!ss_initialized_ptr))
+ panic("SElinux: unable to allocate from pmalloc pool.");
+ *ss_initialized_ptr = false;
+ pmalloc_protect_pool(selinux_pool);
rwlock_init(&selinux_ss.policy_rwlock);
mutex_init(&selinux_ss.status_lock);
*ss = &selinux_ss;
@@ -772,7 +783,7 @@ static int security_compute_validatetrans(struct selinux_state *state,
int rc = 0;


- if (!state->initialized)
+ if (!*ss_initialized_ptr)
return 0;

read_lock(&state->ss->policy_rwlock);
@@ -872,7 +883,7 @@ int security_bounded_transition(struct selinux_state *state,
int index;
int rc;

- if (!state->initialized)
+ if (!*ss_initialized_ptr)
return 0;

read_lock(&state->ss->policy_rwlock);
@@ -1032,7 +1043,7 @@ void security_compute_xperms_decision(struct selinux_state *state,
memset(xpermd->dontaudit->p, 0, sizeof(xpermd->dontaudit->p));

read_lock(&state->ss->policy_rwlock);
- if (!state->initialized)
+ if (!*ss_initialized_ptr)
goto allow;

policydb = &state->ss->policydb;
@@ -1121,7 +1132,7 @@ void security_compute_av(struct selinux_state *state,
read_lock(&state->ss->policy_rwlock);
avd_init(state, avd);
xperms->len = 0;
- if (!state->initialized)
+ if (!*ss_initialized_ptr)
goto allow;

policydb = &state->ss->policydb;
@@ -1175,7 +1186,7 @@ void security_compute_av_user(struct selinux_state *state,

read_lock(&state->ss->policy_rwlock);
avd_init(state, avd);
- if (!state->initialized)
+ if (!*ss_initialized_ptr)
goto allow;

policydb = &state->ss->policydb;
@@ -1294,7 +1305,7 @@ static int security_sid_to_context_core(struct selinux_state *state,
*scontext = NULL;
*scontext_len = 0;

- if (!state->initialized) {
+ if (!*ss_initialized_ptr) {
if (sid <= SECINITSID_NUM) {
char *scontextp;

@@ -1466,7 +1477,7 @@ static int security_context_to_sid_core(struct selinux_state *state,
if (!scontext2)
return -ENOMEM;

- if (!state->initialized) {
+ if (!*ss_initialized_ptr) {
int i;

for (i = 1; i < SECINITSID_NUM; i++) {
@@ -1648,7 +1659,7 @@ static int security_compute_sid(struct selinux_state *state,
int rc = 0;
bool sock;

- if (!state->initialized) {
+ if (!*ss_initialized_ptr) {
switch (orig_tclass) {
case SECCLASS_PROCESS: /* kernel value */
*out_sid = ssid;
@@ -2128,7 +2139,8 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len)
policydb = &state->ss->policydb;
sidtab = &state->ss->sidtab;

- if (!state->initialized) {
+ if (!*ss_initialized_ptr) {
+ bool dummy_initialized = true;
rc = policydb_read(policydb, fp);
if (rc)
goto out;
@@ -2148,7 +2160,8 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len)
}

security_load_policycaps(state);
- state->initialized = 1;
+ pmalloc_rare_write(selinux_pool, ss_initialized_ptr,
+ &dummy_initialized, sizeof(bool));
seqno = ++state->ss->latest_granting;
selinux_complete_init();
avc_ss_reset(state->avc, seqno);
@@ -2578,7 +2591,7 @@ int security_get_user_sids(struct selinux_state *state,
*sids = NULL;
*nel = 0;

- if (!state->initialized)
+ if (!*ss_initialized_ptr)
goto out;

read_lock(&state->ss->policy_rwlock);
@@ -2812,7 +2825,7 @@ int security_get_bools(struct selinux_state *state,
struct policydb *policydb;
int i, rc;

- if (!state->initialized) {
+ if (!*ss_initialized_ptr) {
*len = 0;
*names = NULL;
*values = NULL;
@@ -2987,7 +3000,7 @@ int security_sid_mls_copy(struct selinux_state *state,
int rc;

rc = 0;
- if (!state->initialized || !policydb->mls_enabled) {
+ if (!*ss_initialized_ptr || !policydb->mls_enabled) {
*new_sid = sid;
goto out;
}
@@ -3094,7 +3107,7 @@ int security_net_peersid_resolve(struct selinux_state *state,
/*
* We don't need to check initialized here since the only way both
* nlbl_sid and xfrm_sid are not equal to SECSID_NULL would be if the
- * security server was initialized and state->initialized was true.
+ * security server was initialized and *ss_initialized_ptr was true.
*/
if (!policydb->mls_enabled)
return 0;
@@ -3149,7 +3162,7 @@ int security_get_classes(struct selinux_state *state,
struct policydb *policydb = &state->ss->policydb;
int rc;

- if (!state->initialized) {
+ if (!*ss_initialized_ptr) {
*nclasses = 0;
*classes = NULL;
return 0;
@@ -3298,7 +3311,7 @@ int selinux_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)

*rule = NULL;

- if (!state->initialized)
+ if (!*ss_initialized_ptr)
return -EOPNOTSUPP;

switch (field) {
@@ -3598,7 +3611,7 @@ int security_netlbl_secattr_to_sid(struct selinux_state *state,
struct context *ctx;
struct context ctx_new;

- if (!state->initialized) {
+ if (!*ss_initialized_ptr) {
*sid = SECSID_NULL;
return 0;
}
@@ -3665,7 +3678,7 @@ int security_netlbl_sid_to_secattr(struct selinux_state *state,
int rc;
struct context *ctx;

- if (!state->initialized)
+ if (!*ss_initialized_ptr)
return 0;

read_lock(&state->ss->policy_rwlock);
@@ -3704,7 +3717,7 @@ int security_read_policy(struct selinux_state *state,
int rc;
struct policy_file fp;

- if (!state->initialized)
+ if (!*ss_initialized_ptr)
return -EINVAL;

*len = security_policydb_len(state);
--
2.14.1
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