AppArmor: dfa match engine

A basic dfa matching engine based off the dfa engine in the Dragon
Book.  It uses simple row comb compression with a check field.

This allows AppArmor to do pattern matching in linear time, and also
avoids stack issues that an nfa based engine may have.  The dfa
engine uses a byte based comparison, with all values being valid.
Any potential character encoding are handled user side when the dfa
tables are created.  By convention AppArmor uses \0 to separate two
dependent path matches since \0 is not a valid path character
(this is done in the link permission check).

The dfa tables are generated in user space and are verified at load
time to be internally consistent.

There are several future improvements planned for the dfa engine:
* The dfa engine may be converted to a hybrid nfa-dfa engine, with
  a fixed size limited stack.  This would allow for size time
  tradeoffs, by inserting limited nfa states to help control
  state explosion that can occur with dfas.
* The dfa engine may pickup the ability to do limited dynamic
  variable matching, instead of fixing all variables at policy
  load time.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 132 insertions, 0 deletions

diff --git a/security/apparmor/include/match.h b/security/apparmor/include/match.h
new file mode 100644
index 000000000000..734a6d35112c
--- /dev/null
+++ b/security/apparmor/include/match.h
@@ -0,0 +1,132 @@
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor policy dfa matching engine definitions.
+ *
+ * Copyright (C) 1998-2008 Novell/SUSE
+ * Copyright 2009-2010 Canonical Ltd.
+ *
+ * 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 of the
+ * License.
+ */
+
+#ifndef __AA_MATCH_H
+#define __AA_MATCH_H
+
+#include <linux/workqueue.h>
+
+#define DFA_NOMATCH                     0
+#define DFA_START                       1
+
+#define DFA_VALID_PERM_MASK             0xffffffff
+#define DFA_VALID_PERM2_MASK            0xffffffff
+
+/**
+ * The format used for transition tables is based on the GNU flex table
+ * file format (--tables-file option; see Table File Format in the flex
+ * info pages and the flex sources for documentation). The magic number
+ * used in the header is 0x1B5E783D insted of 0xF13C57B1 though, because
+ * the YY_ID_CHK (check) and YY_ID_DEF (default) tables are used
+ * slightly differently (see the apparmor-parser package).
+ */
+
+#define YYTH_MAGIC      0x1B5E783D
+#define YYTH_DEF_RECURSE 0x1                    /* DEF Table is recursive */
+
+struct table_set_header {
+        u32 th_magic;           /* YYTH_MAGIC */
+        u32 th_hsize;
+        u32 th_ssize;
+        u16 th_flags;
+        char th_version[];
+};
+
+/* The YYTD_ID are one less than flex table mappings.  The flex id
+ * has 1 subtracted at table load time, this allows us to directly use the
+ * ID's as indexes.
+ */
+#define YYTD_ID_ACCEPT  0
+#define YYTD_ID_BASE    1
+#define YYTD_ID_CHK     2
+#define YYTD_ID_DEF     3
+#define YYTD_ID_EC      4
+#define YYTD_ID_META    5
+#define YYTD_ID_ACCEPT2 6
+#define YYTD_ID_NXT     7
+#define YYTD_ID_TSIZE   8
+
+#define YYTD_DATA8      1
+#define YYTD_DATA16     2
+#define YYTD_DATA32     4
+#define YYTD_DATA64     8
+
+/* Each ACCEPT2 table gets 6 dedicated flags, YYTD_DATAX define the
+ * first flags
+ */
+#define ACCEPT1_FLAGS(X) ((X) & 0x3f)
+#define ACCEPT2_FLAGS(X) ACCEPT1_FLAGS((X) >> YYTD_ID_ACCEPT2)
+#define TO_ACCEPT1_FLAG(X) ACCEPT1_FLAGS(X)
+#define TO_ACCEPT2_FLAG(X) (ACCEPT1_FLAGS(X) << YYTD_ID_ACCEPT2)
+#define DFA_FLAG_VERIFY_STATES 0x1000
+
+struct table_header {
+        u16 td_id;
+        u16 td_flags;
+        u32 td_hilen;
+        u32 td_lolen;
+        char td_data[];
+};
+
+#define DEFAULT_TABLE(DFA) ((u16 *)((DFA)->tables[YYTD_ID_DEF]->td_data))
+#define BASE_TABLE(DFA) ((u32 *)((DFA)->tables[YYTD_ID_BASE]->td_data))
+#define NEXT_TABLE(DFA) ((u16 *)((DFA)->tables[YYTD_ID_NXT]->td_data))
+#define CHECK_TABLE(DFA) ((u16 *)((DFA)->tables[YYTD_ID_CHK]->td_data))
+#define EQUIV_TABLE(DFA) ((u8 *)((DFA)->tables[YYTD_ID_EC]->td_data))
+#define ACCEPT_TABLE(DFA) ((u32 *)((DFA)->tables[YYTD_ID_ACCEPT]->td_data))
+#define ACCEPT_TABLE2(DFA) ((u32 *)((DFA)->tables[YYTD_ID_ACCEPT2]->td_data))
+
+struct aa_dfa {
+        struct kref count;
+        u16 flags;
+        struct table_header *tables[YYTD_ID_TSIZE];
+};
+
+#define byte_to_byte(X) (X)
+
+#define UNPACK_ARRAY(TABLE, BLOB, LEN, TYPE, NTOHX) \
+        do { \
+                typeof(LEN) __i; \
+                TYPE *__t = (TYPE *) TABLE; \
+                TYPE *__b = (TYPE *) BLOB; \
+                for (__i = 0; __i < LEN; __i++) { \
+                        __t[__i] = NTOHX(__b[__i]); \
+                } \
+        } while (0)
+
+static inline size_t table_size(size_t len, size_t el_size)
+{
+        return ALIGN(sizeof(struct table_header) + len * el_size, 8);
+}
+
+struct aa_dfa *aa_dfa_unpack(void *blob, size_t size, int flags);
+unsigned int aa_dfa_match_len(struct aa_dfa *dfa, unsigned int start,
+                              const char *str, int len);
+unsigned int aa_dfa_match(struct aa_dfa *dfa, unsigned int start,
+                          const char *str);
+void aa_dfa_free_kref(struct kref *kref);
+
+/**
+ * aa_put_dfa - put a dfa refcount
+ * @dfa: dfa to put refcount   (MAYBE NULL)
+ *
+ * Requires: if @dfa != NULL that a valid refcount be held
+ */
+static inline void aa_put_dfa(struct aa_dfa *dfa)
+{
+        if (dfa)
+                kref_put(&dfa->count, aa_dfa_free_kref);
+}
+
+#endif /* __AA_MATCH_H */