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authorCasey Schaufler <casey@schaufler-ca.com>2008-02-04 22:29:50 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-05 09:44:20 -0800
commite114e473771c848c3cfec05f0123e70f1cdbdc99 (patch)
tree933b840f3ccac6860da56291c742094f9b5a20cb /security/smack/smack_access.c
parenteda61d32e8ad1d9102872f9a0abf3344bf9c5e67 (diff)
downloadlinaro-lsk-e114e473771c848c3cfec05f0123e70f1cdbdc99.tar.gz
Smack: Simplified Mandatory Access Control Kernel
Smack is the Simplified Mandatory Access Control Kernel. Smack implements mandatory access control (MAC) using labels attached to tasks and data containers, including files, SVIPC, and other tasks. Smack is a kernel based scheme that requires an absolute minimum of application support and a very small amount of configuration data. Smack uses extended attributes and provides a set of general mount options, borrowing technics used elsewhere. Smack uses netlabel for CIPSO labeling. Smack provides a pseudo-filesystem smackfs that is used for manipulation of system Smack attributes. The patch, patches for ls and sshd, a README, a startup script, and x86 binaries for ls and sshd are also available on http://www.schaufler-ca.com Development has been done using Fedora Core 7 in a virtual machine environment and on an old Sony laptop. Smack provides mandatory access controls based on the label attached to a task and the label attached to the object it is attempting to access. Smack labels are deliberately short (1-23 characters) text strings. Single character labels using special characters are reserved for system use. The only operation applied to Smack labels is equality comparison. No wildcards or expressions, regular or otherwise, are used. Smack labels are composed of printable characters and may not include "/". A file always gets the Smack label of the task that created it. Smack defines and uses these labels: "*" - pronounced "star" "_" - pronounced "floor" "^" - pronounced "hat" "?" - pronounced "huh" The access rules enforced by Smack are, in order: 1. Any access requested by a task labeled "*" is denied. 2. A read or execute access requested by a task labeled "^" is permitted. 3. A read or execute access requested on an object labeled "_" is permitted. 4. Any access requested on an object labeled "*" is permitted. 5. Any access requested by a task on an object with the same label is permitted. 6. Any access requested that is explicitly defined in the loaded rule set is permitted. 7. Any other access is denied. Rules may be explicitly defined by writing subject,object,access triples to /smack/load. Smack rule sets can be easily defined that describe Bell&LaPadula sensitivity, Biba integrity, and a variety of interesting configurations. Smack rule sets can be modified on the fly to accommodate changes in the operating environment or even the time of day. Some practical use cases: Hierarchical levels. The less common of the two usual uses for MLS systems is to define hierarchical levels, often unclassified, confidential, secret, and so on. To set up smack to support this, these rules could be defined: C Unclass rx S C rx S Unclass rx TS S rx TS C rx TS Unclass rx A TS process can read S, C, and Unclass data, but cannot write it. An S process can read C and Unclass. Note that specifying that TS can read S and S can read C does not imply TS can read C, it has to be explicitly stated. Non-hierarchical categories. This is the more common of the usual uses for an MLS system. Since the default rule is that a subject cannot access an object with a different label no access rules are required to implement compartmentalization. A case that the Bell & LaPadula policy does not allow is demonstrated with this Smack access rule: A case that Bell&LaPadula does not allow that Smack does: ESPN ABC r ABC ESPN r On my portable video device I have two applications, one that shows ABC programming and the other ESPN programming. ESPN wants to show me sport stories that show up as news, and ABC will only provide minimal information about a sports story if ESPN is covering it. Each side can look at the other's info, neither can change the other. Neither can see what FOX is up to, which is just as well all things considered. Another case that I especially like: SatData Guard w Guard Publish w A program running with the Guard label opens a UDP socket and accepts messages sent by a program running with a SatData label. The Guard program inspects the message to ensure it is wholesome and if it is sends it to a program running with the Publish label. This program then puts the information passed in an appropriate place. Note that the Guard program cannot write to a Publish file system object because file system semanitic require read as well as write. The four cases (categories, levels, mutual read, guardbox) here are all quite real, and problems I've been asked to solve over the years. The first two are easy to do with traditonal MLS systems while the last two you can't without invoking privilege, at least for a while. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Cc: Joshua Brindle <method@manicmethod.com> Cc: Paul Moore <paul.moore@hp.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Chris Wright <chrisw@sous-sol.org> Cc: James Morris <jmorris@namei.org> Cc: "Ahmed S. Darwish" <darwish.07@gmail.com> Cc: Andrew G. Morgan <morgan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'security/smack/smack_access.c')
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diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
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+/*
+ * 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_unset = {
+ .smk_next = NULL,
+ .smk_known = "UNSET",
+ .smk_secid = 1,
+ .smk_cipso = NULL,
+};
+
+struct smack_known smack_known_huh = {
+ .smk_next = &smack_known_unset,
+ .smk_known = "?",
+ .smk_secid = 2,
+ .smk_cipso = NULL,
+};
+
+struct smack_known smack_known_hat = {
+ .smk_next = &smack_known_huh,
+ .smk_known = "^",
+ .smk_secid = 3,
+ .smk_cipso = NULL,
+};
+
+struct smack_known smack_known_star = {
+ .smk_next = &smack_known_hat,
+ .smk_known = "*",
+ .smk_secid = 4,
+ .smk_cipso = NULL,
+};
+
+struct smack_known smack_known_floor = {
+ .smk_next = &smack_known_star,
+ .smk_known = "_",
+ .smk_secid = 5,
+ .smk_cipso = NULL,
+};
+
+struct smack_known smack_known_invalid = {
+ .smk_next = &smack_known_floor,
+ .smk_known = "",
+ .smk_secid = 6,
+ .smk_cipso = NULL,
+};
+
+struct smack_known *smack_known = &smack_known_invalid;
+
+/*
+ * The initial value needs to be bigger than any of the
+ * known values above.
+ */
+static u32 smack_next_secid = 10;
+
+/**
+ * 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
+ *
+ * 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)
+{
+ u32 may = MAY_NOT;
+ struct smk_list_entry *sp;
+ struct smack_rule *srp;
+
+ /*
+ * 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)
+ return -EACCES;
+ /*
+ * 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)
+ return 0;
+ /*
+ * 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)
+ return 0;
+ /*
+ * 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)
+ return 0;
+ if (subject_label == smack_known_hat.smk_known ||
+ strcmp(subject_label, smack_known_hat.smk_known) == 0)
+ return 0;
+ }
+ /*
+ * 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.
+ */
+ for (sp = smack_list; sp != NULL; sp = sp->smk_next) {
+ srp = &sp->smk_rule;
+
+ 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;
+ }
+ }
+ }
+ /*
+ * This is a bit map operation.
+ */
+ if ((request & may) == request)
+ return 0;
+
+ return -EACCES;
+}
+
+/**
+ * smk_curacc - determine if current has a specific access to an object
+ * @object_label: a pointer to the object's Smack label
+ * @request: the access requested, in "MAY" format
+ *
+ * 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 my have the capability
+ * to override the rules.
+ */
+int smk_curacc(char *obj_label, u32 mode)
+{
+ int rc;
+
+ rc = smk_access(current->security, obj_label, mode);
+ if (rc == 0)
+ return 0;
+
+ if (capable(CAP_MAC_OVERRIDE))
+ return 0;
+
+ return rc;
+}
+
+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] == '/') {
+ smack[i] = '\0';
+ found = 1;
+ } else
+ smack[i] = string[i];
+ }
+
+ if (smack[0] == '\0')
+ return NULL;
+
+ mutex_lock(&smack_known_lock);
+
+ for (skp = smack_known; skp != NULL; skp = skp->smk_next)
+ if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0)
+ break;
+
+ if (skp == NULL) {
+ skp = kzalloc(sizeof(struct smack_known), GFP_KERNEL);
+ if (skp != NULL) {
+ skp->smk_next = smack_known;
+ 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.
+ */
+ smp_mb();
+ smack_known = skp;
+ }
+ }
+
+ 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;
+
+ 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;
+
+ for (skp = smack_known; skp != NULL; skp = skp->smk_next)
+ if (skp->smk_secid == secid)
+ return skp->smk_known;
+
+ /*
+ * If we got this far someone asked for the translation
+ * of a secid that is not on the list.
+ */
+ 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;
+
+ for (skp = smack_known; skp != NULL; skp = skp->smk_next)
+ if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0)
+ return skp->smk_secid;
+ 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;
+
+ for (kp = smack_known; final == NULL && kp != NULL; kp = kp->smk_next) {
+ 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);
+ }
+ 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;
+
+ for (kp = smack_known; kp != NULL; kp = kp->smk_next)
+ if (kp->smk_known == smack ||
+ strcmp(kp->smk_known, smack) == 0)
+ break;
+
+ if (kp == NULL || kp->smk_cipso == NULL)
+ return -ENOENT;
+
+ memcpy(cp, kp->smk_cipso, sizeof(struct smack_cipso));
+ return 0;
+}