linux/security/smack/smack_access.c
Etienne Basset ecfcc53fef smack: implement logging V3
the following patch, add logging of Smack security decisions.
This is of course very useful to understand what your current smack policy does.
As suggested by Casey, it also now forbids labels with ', " or \

It introduces a '/smack/logging' switch :
0: no logging
1: log denied (default)
2: log accepted
3: log denied&accepted

Signed-off-by: Etienne Basset <etienne.basset@numericable.fr>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
2009-04-14 09:00:23 +10:00

502 lines
13 KiB
C

/*
* Copyright (C) 2007 Casey Schaufler <casey@schaufler-ca.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, version 2.
*
* Author:
* Casey Schaufler <casey@schaufler-ca.com>
*
*/
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include "smack.h"
struct smack_known smack_known_huh = {
.smk_known = "?",
.smk_secid = 2,
.smk_cipso = NULL,
};
struct smack_known smack_known_hat = {
.smk_known = "^",
.smk_secid = 3,
.smk_cipso = NULL,
};
struct smack_known smack_known_star = {
.smk_known = "*",
.smk_secid = 4,
.smk_cipso = NULL,
};
struct smack_known smack_known_floor = {
.smk_known = "_",
.smk_secid = 5,
.smk_cipso = NULL,
};
struct smack_known smack_known_invalid = {
.smk_known = "",
.smk_secid = 6,
.smk_cipso = NULL,
};
struct smack_known smack_known_web = {
.smk_known = "@",
.smk_secid = 7,
.smk_cipso = NULL,
};
LIST_HEAD(smack_known_list);
/*
* The initial value needs to be bigger than any of the
* known values above.
*/
static u32 smack_next_secid = 10;
/*
* what events do we log
* can be overwritten at run-time by /smack/logging
*/
int log_policy = SMACK_AUDIT_DENIED;
/**
* smk_access - determine if a subject has a specific access to an object
* @subject_label: a pointer to the subject's Smack label
* @object_label: a pointer to the object's Smack label
* @request: the access requested, in "MAY" format
* @a : a pointer to the audit data
*
* This function looks up the subject/object pair in the
* access rule list and returns 0 if the access is permitted,
* non zero otherwise.
*
* Even though Smack labels are usually shared on smack_list
* labels that come in off the network can't be imported
* and added to the list for locking reasons.
*
* Therefore, it is necessary to check the contents of the labels,
* not just the pointer values. Of course, in most cases the labels
* will be on the list, so checking the pointers may be a worthwhile
* optimization.
*/
int smk_access(char *subject_label, char *object_label, int request,
struct smk_audit_info *a)
{
u32 may = MAY_NOT;
struct smack_rule *srp;
int rc = 0;
/*
* Hardcoded comparisons.
*
* A star subject can't access any object.
*/
if (subject_label == smack_known_star.smk_known ||
strcmp(subject_label, smack_known_star.smk_known) == 0) {
rc = -EACCES;
goto out_audit;
}
/*
* An internet object can be accessed by any subject.
* Tasks cannot be assigned the internet label.
* An internet subject can access any object.
*/
if (object_label == smack_known_web.smk_known ||
subject_label == smack_known_web.smk_known ||
strcmp(object_label, smack_known_web.smk_known) == 0 ||
strcmp(subject_label, smack_known_web.smk_known) == 0)
goto out_audit;
/*
* A star object can be accessed by any subject.
*/
if (object_label == smack_known_star.smk_known ||
strcmp(object_label, smack_known_star.smk_known) == 0)
goto out_audit;
/*
* An object can be accessed in any way by a subject
* with the same label.
*/
if (subject_label == object_label ||
strcmp(subject_label, object_label) == 0)
goto out_audit;
/*
* A hat subject can read any object.
* A floor object can be read by any subject.
*/
if ((request & MAY_ANYREAD) == request) {
if (object_label == smack_known_floor.smk_known ||
strcmp(object_label, smack_known_floor.smk_known) == 0)
goto out_audit;
if (subject_label == smack_known_hat.smk_known ||
strcmp(subject_label, smack_known_hat.smk_known) == 0)
goto out_audit;
}
/*
* Beyond here an explicit relationship is required.
* If the requested access is contained in the available
* access (e.g. read is included in readwrite) it's
* good.
*/
rcu_read_lock();
list_for_each_entry_rcu(srp, &smack_rule_list, list) {
if (srp->smk_subject == subject_label ||
strcmp(srp->smk_subject, subject_label) == 0) {
if (srp->smk_object == object_label ||
strcmp(srp->smk_object, object_label) == 0) {
may = srp->smk_access;
break;
}
}
}
rcu_read_unlock();
/*
* This is a bit map operation.
*/
if ((request & may) == request)
goto out_audit;
rc = -EACCES;
out_audit:
#ifdef CONFIG_AUDIT
if (a)
smack_log(subject_label, object_label, request, rc, a);
#endif
return rc;
}
/**
* smk_curacc - determine if current has a specific access to an object
* @obj_label: a pointer to the object's Smack label
* @mode: the access requested, in "MAY" format
* @a : common audit data
*
* This function checks the current subject label/object label pair
* in the access rule list and returns 0 if the access is permitted,
* non zero otherwise. It allows that current may have the capability
* to override the rules.
*/
int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
{
int rc;
char *sp = current_security();
rc = smk_access(sp, obj_label, mode, NULL);
if (rc == 0)
goto out_audit;
/*
* Return if a specific label has been designated as the
* only one that gets privilege and current does not
* have that label.
*/
if (smack_onlycap != NULL && smack_onlycap != current->cred->security)
goto out_audit;
if (capable(CAP_MAC_OVERRIDE))
return 0;
out_audit:
#ifdef CONFIG_AUDIT
if (a)
smack_log(sp, obj_label, mode, rc, a);
#endif
return rc;
}
#ifdef CONFIG_AUDIT
/**
* smack_str_from_perm : helper to transalate an int to a
* readable string
* @string : the string to fill
* @access : the int
*
*/
static inline void smack_str_from_perm(char *string, int access)
{
int i = 0;
if (access & MAY_READ)
string[i++] = 'r';
if (access & MAY_WRITE)
string[i++] = 'w';
if (access & MAY_EXEC)
string[i++] = 'x';
if (access & MAY_APPEND)
string[i++] = 'a';
string[i] = '\0';
}
/**
* smack_log_callback - SMACK specific information
* will be called by generic audit code
* @ab : the audit_buffer
* @a : audit_data
*
*/
static void smack_log_callback(struct audit_buffer *ab, void *a)
{
struct common_audit_data *ad = a;
struct smack_audit_data *sad = &ad->lsm_priv.smack_audit_data;
audit_log_format(ab, "lsm=SMACK fn=%s action=%s", ad->function,
sad->result ? "denied" : "granted");
audit_log_format(ab, " subject=");
audit_log_untrustedstring(ab, sad->subject);
audit_log_format(ab, " object=");
audit_log_untrustedstring(ab, sad->object);
audit_log_format(ab, " requested=%s", sad->request);
}
/**
* smack_log - Audit the granting or denial of permissions.
* @subject_label : smack label of the requester
* @object_label : smack label of the object being accessed
* @request: requested permissions
* @result: result from smk_access
* @a: auxiliary audit data
*
* Audit the granting or denial of permissions in accordance
* with the policy.
*/
void smack_log(char *subject_label, char *object_label, int request,
int result, struct smk_audit_info *ad)
{
char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
struct smack_audit_data *sad;
struct common_audit_data *a = &ad->a;
/* check if we have to log the current event */
if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
return;
if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
return;
if (a->function == NULL)
a->function = "unknown";
/* end preparing the audit data */
sad = &a->lsm_priv.smack_audit_data;
smack_str_from_perm(request_buffer, request);
sad->subject = subject_label;
sad->object = object_label;
sad->request = request_buffer;
sad->result = result;
a->lsm_pre_audit = smack_log_callback;
common_lsm_audit(a);
}
#else /* #ifdef CONFIG_AUDIT */
void smack_log(char *subject_label, char *object_label, int request,
int result, struct smk_audit_info *ad)
{
}
#endif
static DEFINE_MUTEX(smack_known_lock);
/**
* smk_import_entry - import a label, return the list entry
* @string: a text string that might be a Smack label
* @len: the maximum size, or zero if it is NULL terminated.
*
* Returns a pointer to the entry in the label list that
* matches the passed string, adding it if necessary.
*/
struct smack_known *smk_import_entry(const char *string, int len)
{
struct smack_known *skp;
char smack[SMK_LABELLEN];
int found;
int i;
if (len <= 0 || len > SMK_MAXLEN)
len = SMK_MAXLEN;
for (i = 0, found = 0; i < SMK_LABELLEN; i++) {
if (found)
smack[i] = '\0';
else if (i >= len || string[i] > '~' || string[i] <= ' ' ||
string[i] == '/' || string[i] == '"' ||
string[i] == '\\' || string[i] == '\'') {
smack[i] = '\0';
found = 1;
} else
smack[i] = string[i];
}
if (smack[0] == '\0')
return NULL;
mutex_lock(&smack_known_lock);
found = 0;
list_for_each_entry_rcu(skp, &smack_known_list, list) {
if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0) {
found = 1;
break;
}
}
if (found == 0) {
skp = kzalloc(sizeof(struct smack_known), GFP_KERNEL);
if (skp != NULL) {
strncpy(skp->smk_known, smack, SMK_MAXLEN);
skp->smk_secid = smack_next_secid++;
skp->smk_cipso = NULL;
spin_lock_init(&skp->smk_cipsolock);
/*
* Make sure that the entry is actually
* filled before putting it on the list.
*/
list_add_rcu(&skp->list, &smack_known_list);
}
}
mutex_unlock(&smack_known_lock);
return skp;
}
/**
* smk_import - import a smack label
* @string: a text string that might be a Smack label
* @len: the maximum size, or zero if it is NULL terminated.
*
* Returns a pointer to the label in the label list that
* matches the passed string, adding it if necessary.
*/
char *smk_import(const char *string, int len)
{
struct smack_known *skp;
/* labels cannot begin with a '-' */
if (string[0] == '-')
return NULL;
skp = smk_import_entry(string, len);
if (skp == NULL)
return NULL;
return skp->smk_known;
}
/**
* smack_from_secid - find the Smack label associated with a secid
* @secid: an integer that might be associated with a Smack label
*
* Returns a pointer to the appropraite Smack label if there is one,
* otherwise a pointer to the invalid Smack label.
*/
char *smack_from_secid(const u32 secid)
{
struct smack_known *skp;
rcu_read_lock();
list_for_each_entry_rcu(skp, &smack_known_list, list) {
if (skp->smk_secid == secid) {
rcu_read_unlock();
return skp->smk_known;
}
}
/*
* If we got this far someone asked for the translation
* of a secid that is not on the list.
*/
rcu_read_unlock();
return smack_known_invalid.smk_known;
}
/**
* smack_to_secid - find the secid associated with a Smack label
* @smack: the Smack label
*
* Returns the appropriate secid if there is one,
* otherwise 0
*/
u32 smack_to_secid(const char *smack)
{
struct smack_known *skp;
rcu_read_lock();
list_for_each_entry_rcu(skp, &smack_known_list, list) {
if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0) {
rcu_read_unlock();
return skp->smk_secid;
}
}
rcu_read_unlock();
return 0;
}
/**
* smack_from_cipso - find the Smack label associated with a CIPSO option
* @level: Bell & LaPadula level from the network
* @cp: Bell & LaPadula categories from the network
* @result: where to put the Smack value
*
* This is a simple lookup in the label table.
*
* This is an odd duck as far as smack handling goes in that
* it sends back a copy of the smack label rather than a pointer
* to the master list. This is done because it is possible for
* a foreign host to send a smack label that is new to this
* machine and hence not on the list. That would not be an
* issue except that adding an entry to the master list can't
* be done at that point.
*/
void smack_from_cipso(u32 level, char *cp, char *result)
{
struct smack_known *kp;
char *final = NULL;
rcu_read_lock();
list_for_each_entry(kp, &smack_known_list, list) {
if (kp->smk_cipso == NULL)
continue;
spin_lock_bh(&kp->smk_cipsolock);
if (kp->smk_cipso->smk_level == level &&
memcmp(kp->smk_cipso->smk_catset, cp, SMK_LABELLEN) == 0)
final = kp->smk_known;
spin_unlock_bh(&kp->smk_cipsolock);
}
rcu_read_unlock();
if (final == NULL)
final = smack_known_huh.smk_known;
strncpy(result, final, SMK_MAXLEN);
return;
}
/**
* smack_to_cipso - find the CIPSO option to go with a Smack label
* @smack: a pointer to the smack label in question
* @cp: where to put the result
*
* Returns zero if a value is available, non-zero otherwise.
*/
int smack_to_cipso(const char *smack, struct smack_cipso *cp)
{
struct smack_known *kp;
int found = 0;
rcu_read_lock();
list_for_each_entry_rcu(kp, &smack_known_list, list) {
if (kp->smk_known == smack ||
strcmp(kp->smk_known, smack) == 0) {
found = 1;
break;
}
}
rcu_read_unlock();
if (found == 0 || kp->smk_cipso == NULL)
return -ENOENT;
memcpy(cp, kp->smk_cipso, sizeof(struct smack_cipso));
return 0;
}