apparmor: isolate policy backwards compatibility to its own file

The details of mapping old policy into newer policy formats clutters
up the unpack code and makes it possible to accidentally use old
mappings in code, so isolate the mapping code into its own file.

This will become more important when the dfa remapping code lands,
as it will greatly expand the compat code base.
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/Makefile

@@ -5,7 +5,8 @@ obj-$(CONFIG_SECURITY_APPARMOR) += apparmor.o
 
 apparmor-y := apparmorfs.o audit.o capability.o task.o ipc.o lib.o match.o \
               path.o domain.o policy.o policy_unpack.o procattr.o lsm.o \
-              resource.o secid.o file.o policy_ns.o label.o mount.o net.o
+              resource.o secid.o file.o policy_ns.o label.o mount.o net.o \
+              policy_compat.o
 apparmor-$(CONFIG_SECURITY_APPARMOR_HASH) += crypto.o
 
 clean-files := capability_names.h rlim_names.h net_names.h

security/apparmor/include/policy_compat.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * AppArmor security module
+ *
+ * Code to provide backwards compatibility with older policy versions,
+ * by converting/mapping older policy formats into the newer internal
+ * formats.
+ *
+ * Copyright 2022 Canonical Ltd.
+ */
+
+#ifndef __POLICY_COMPAT_H
+#define __POLICY_COMPAT_H
+
+#include "policy.h"
+
+#define K_ABI_MASK 0x3ff
+#define FORCE_COMPLAIN_FLAG 0x800
+#define VERSION_LT(X, Y) (((X) & K_ABI_MASK) < ((Y) & K_ABI_MASK))
+#define VERSION_LE(X, Y) (((X) & K_ABI_MASK) <= ((Y) & K_ABI_MASK))
+#define VERSION_GT(X, Y) (((X) & K_ABI_MASK) > ((Y) & K_ABI_MASK))
+
+#define v5	5	/* base version */
+#define v6	6	/* per entry policydb mediation check */
+#define v7	7
+#define v8	8	/* full network masking */
+#define v9	9	/* xbits are used as permission bits in policydb */
+
+int aa_compat_map_xmatch(struct aa_policydb *policy);
+int aa_compat_map_policy(struct aa_policydb *policy, u32 version);
+int aa_compat_map_file(struct aa_policydb *policy);
+
+#endif /* __POLICY_COMPAT_H */

security/apparmor/include/policy_unpack.h

@@ -16,6 +16,7 @@
 #include <linux/dcache.h>
 #include <linux/workqueue.h>
 
+
 struct aa_load_ent {
 	struct list_head list;
 	struct aa_profile *new;

security/apparmor/policy_compat.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor functions for unpacking policy loaded
+ * from userspace.
+ *
+ * Copyright (C) 1998-2008 Novell/SUSE
+ * Copyright 2009-2022 Canonical Ltd.
+ *
+ * Code to provide backwards compatibility with older policy versions,
+ * by converting/mapping older policy formats into the newer internal
+ * formats.
+ */
+
+#include <linux/ctype.h>
+#include <linux/errno.h>
+
+#include "include/lib.h"
+#include "include/policy_unpack.h"
+#include "include/policy_compat.h"
+
+/* remap old accept table embedded permissions to separate permission table */
+static u32 dfa_map_xindex(u16 mask)
+{
+	u16 old_index = (mask >> 10) & 0xf;
+	u32 index = 0;
+
+	if (mask & 0x100)
+		index |= AA_X_UNSAFE;
+	if (mask & 0x200)
+		index |= AA_X_INHERIT;
+	if (mask & 0x80)
+		index |= AA_X_UNCONFINED;
+
+	if (old_index == 1) {
+		index |= AA_X_UNCONFINED;
+	} else if (old_index == 2) {
+		index |= AA_X_NAME;
+	} else if (old_index == 3) {
+		index |= AA_X_NAME | AA_X_CHILD;
+	} else if (old_index) {
+		index |= AA_X_TABLE;
+		index |= old_index - 4;
+	}
+
+	return index;
+}
+
+/*
+ * map old dfa inline permissions to new format
+ */
+#define dfa_user_allow(dfa, state) (((ACCEPT_TABLE(dfa)[state]) & 0x7f) | \
+				    ((ACCEPT_TABLE(dfa)[state]) & 0x80000000))
+#define dfa_user_xbits(dfa, state) (((ACCEPT_TABLE(dfa)[state]) >> 7) & 0x7f)
+#define dfa_user_audit(dfa, state) ((ACCEPT_TABLE2(dfa)[state]) & 0x7f)
+#define dfa_user_quiet(dfa, state) (((ACCEPT_TABLE2(dfa)[state]) >> 7) & 0x7f)
+#define dfa_user_xindex(dfa, state) \
+	(dfa_map_xindex(ACCEPT_TABLE(dfa)[state] & 0x3fff))
+
+#define dfa_other_allow(dfa, state) ((((ACCEPT_TABLE(dfa)[state]) >> 14) & \
+				      0x7f) |				\
+				     ((ACCEPT_TABLE(dfa)[state]) & 0x80000000))
+#define dfa_other_xbits(dfa, state) \
+	((((ACCEPT_TABLE(dfa)[state]) >> 7) >> 14) & 0x7f)
+#define dfa_other_audit(dfa, state) (((ACCEPT_TABLE2(dfa)[state]) >> 14) & 0x7f)
+#define dfa_other_quiet(dfa, state) \
+	((((ACCEPT_TABLE2(dfa)[state]) >> 7) >> 14) & 0x7f)
+#define dfa_other_xindex(dfa, state) \
+	dfa_map_xindex((ACCEPT_TABLE(dfa)[state] >> 14) & 0x3fff)
+
+/**
+ * map_old_perms - map old file perms layout to the new layout
+ * @old: permission set in old mapping
+ *
+ * Returns: new permission mapping
+ */
+static u32 map_old_perms(u32 old)
+{
+	u32 new = old & 0xf;
+
+	if (old & MAY_READ)
+		new |= AA_MAY_GETATTR | AA_MAY_OPEN;
+	if (old & MAY_WRITE)
+		new |= AA_MAY_SETATTR | AA_MAY_CREATE | AA_MAY_DELETE |
+		       AA_MAY_CHMOD | AA_MAY_CHOWN | AA_MAY_OPEN;
+	if (old & 0x10)
+		new |= AA_MAY_LINK;
+	/* the old mapping lock and link_subset flags where overlaid
+	 * and use was determined by part of a pair that they were in
+	 */
+	if (old & 0x20)
+		new |= AA_MAY_LOCK | AA_LINK_SUBSET;
+	if (old & 0x40)	/* AA_EXEC_MMAP */
+		new |= AA_EXEC_MMAP;
+
+	return new;
+}
+
+static void compute_fperms_allow(struct aa_perms *perms, struct aa_dfa *dfa,
+				 aa_state_t state)
+{
+	perms->allow |= AA_MAY_GETATTR;
+
+	/* change_profile wasn't determined by ownership in old mapping */
+	if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
+		perms->allow |= AA_MAY_CHANGE_PROFILE;
+	if (ACCEPT_TABLE(dfa)[state] & 0x40000000)
+		perms->allow |= AA_MAY_ONEXEC;
+}
+
+static struct aa_perms compute_fperms_user(struct aa_dfa *dfa,
+					   aa_state_t state)
+{
+	struct aa_perms perms = { };
+
+	perms.allow = map_old_perms(dfa_user_allow(dfa, state));
+	perms.audit = map_old_perms(dfa_user_audit(dfa, state));
+	perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
+	perms.xindex = dfa_user_xindex(dfa, state);
+
+	compute_fperms_allow(&perms, dfa, state);
+
+	return perms;
+}
+
+static struct aa_perms compute_fperms_other(struct aa_dfa *dfa,
+					    aa_state_t state)
+{
+	struct aa_perms perms = { };
+
+	perms.allow = map_old_perms(dfa_other_allow(dfa, state));
+	perms.audit = map_old_perms(dfa_other_audit(dfa, state));
+	perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
+	perms.xindex = dfa_other_xindex(dfa, state);
+
+	compute_fperms_allow(&perms, dfa, state);
+
+	return perms;
+}
+
+/**
+ * aa_compute_fperms - convert dfa compressed perms to internal perms and store
+ *		       them so they can be retrieved later.
+ * @dfa: a dfa using fperms to remap to internal permissions
+ *
+ * Returns: remapped perm table
+ */
+static struct aa_perms *compute_fperms(struct aa_dfa *dfa)
+{
+	aa_state_t state;
+	unsigned int state_count;
+	struct aa_perms *table;
+
+	AA_BUG(!dfa);
+
+	state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
+	/* DFAs are restricted from having a state_count of less than 2 */
+	table = kvcalloc(state_count * 2, sizeof(struct aa_perms), GFP_KERNEL);
+	if (!table)
+		return NULL;
+
+	/* zero init so skip the trap state (state == 0) */
+	for (state = 1; state < state_count; state++) {
+		table[state * 2] = compute_fperms_user(dfa, state);
+		table[state * 2 + 1] = compute_fperms_other(dfa, state);
+	}
+
+	return table;
+}
+
+static struct aa_perms *compute_xmatch_perms(struct aa_dfa *xmatch)
+{
+	struct aa_perms *perms;
+	int state;
+	int state_count;
+
+	AA_BUG(!xmatch);
+
+	state_count = xmatch->tables[YYTD_ID_BASE]->td_lolen;
+	/* DFAs are restricted from having a state_count of less than 2 */
+	perms = kvcalloc(state_count, sizeof(struct aa_perms), GFP_KERNEL);
+
+	/* zero init so skip the trap state (state == 0) */
+	for (state = 1; state < state_count; state++)
+		perms[state].allow = dfa_user_allow(xmatch, state);
+
+	return perms;
+}
+
+static u32 map_other(u32 x)
+{
+	return ((x & 0x3) << 8) |	/* SETATTR/GETATTR */
+		((x & 0x1c) << 18) |	/* ACCEPT/BIND/LISTEN */
+		((x & 0x60) << 19);	/* SETOPT/GETOPT */
+}
+
+static u32 map_xbits(u32 x)
+{
+	return ((x & 0x1) << 7) |
+		((x & 0x7e) << 9);
+}
+
+static struct aa_perms compute_perms_entry(struct aa_dfa *dfa,
+					   aa_state_t state,
+					   u32 version)
+{
+	struct aa_perms perms = { };
+
+	perms.allow = dfa_user_allow(dfa, state);
+	perms.audit = dfa_user_audit(dfa, state);
+	perms.quiet = dfa_user_quiet(dfa, state);
+
+	/*
+	 * This mapping is convulated due to history.
+	 * v1-v4: only file perms, which are handled by compute_fperms
+	 * v5: added policydb which dropped user conditional to gain new
+	 *     perm bits, but had to map around the xbits because the
+	 *     userspace compiler was still munging them.
+	 * v9: adds using the xbits in policydb because the compiler now
+	 *     supports treating policydb permission bits different.
+	 *     Unfortunately there is no way to force auditing on the
+	 *     perms represented by the xbits
+	 */
+	perms.allow |= map_other(dfa_other_allow(dfa, state));
+	if (VERSION_LE(version, v8))
+		perms.allow |= AA_MAY_LOCK;
+	else
+		perms.allow |= map_xbits(dfa_user_xbits(dfa, state));
+
+	/*
+	 * for v5-v9 perm mapping in the policydb, the other set is used
+	 * to extend the general perm set
+	 */
+	perms.audit |= map_other(dfa_other_audit(dfa, state));
+	perms.quiet |= map_other(dfa_other_quiet(dfa, state));
+	if (VERSION_GT(version, v8))
+		perms.quiet |= map_xbits(dfa_other_xbits(dfa, state));
+
+	return perms;
+}
+
+static struct aa_perms *compute_perms(struct aa_dfa *dfa, u32 version)
+{
+	unsigned int state;
+	unsigned int state_count;
+	struct aa_perms *table;
+
+	AA_BUG(!dfa);
+
+	state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
+	/* DFAs are restricted from having a state_count of less than 2 */
+	table = kvcalloc(state_count, sizeof(struct aa_perms), GFP_KERNEL);
+	if (!table)
+		return NULL;
+
+	/* zero init so skip the trap state (state == 0) */
+	for (state = 1; state < state_count; state++)
+		table[state] = compute_perms_entry(dfa, state, version);
+
+	return table;
+}
+
+/**
+ * remap_dfa_accept - remap old dfa accept table to be an index
+ * @dfa: dfa to do the remapping on
+ * @factor: scaling factor for the index conversion.
+ *
+ * Used in conjunction with compute_Xperms, it converts old style perms
+ * that are encoded in the dfa accept tables to the new style where
+ * there is a permission table and the accept table is an index into
+ * the permission table.
+ */
+static void remap_dfa_accept(struct aa_dfa *dfa, unsigned int factor)
+{
+	unsigned int state;
+	unsigned int state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
+
+	AA_BUG(!dfa);
+
+	for (state = 0; state < state_count; state++)
+		ACCEPT_TABLE(dfa)[state] = state * factor;
+	kvfree(dfa->tables[YYTD_ID_ACCEPT2]);
+	dfa->tables[YYTD_ID_ACCEPT2] = NULL;
+}
+
+/* TODO: merge different dfa mappings into single map_policy fn */
+int aa_compat_map_xmatch(struct aa_policydb *policy)
+{
+	policy->perms = compute_xmatch_perms(policy->dfa);
+	if (!policy->perms)
+		return -ENOMEM;
+
+	remap_dfa_accept(policy->dfa, 1);
+
+	return 0;
+}
+
+int aa_compat_map_policy(struct aa_policydb *policy, u32 version)
+{
+	policy->perms = compute_perms(policy->dfa, version);
+	if (!policy->perms)
+		return -ENOMEM;
+
+	remap_dfa_accept(policy->dfa, 1);
+
+	return 0;
+}
+
+int aa_compat_map_file(struct aa_policydb *policy)
+{
+	policy->perms = compute_fperms(policy->dfa);
+	if (!policy->perms)
+		return -ENOMEM;
+
+	remap_dfa_accept(policy->dfa, 2);
+
+	return 0;
+}