AppArmor: policy routines for loading and unpacking policy

AppArmor policy is loaded in a platform independent flattened binary
stream. Verify and unpack the data converting it to the internal
format needed for enforcement.

Signed-off-by: John Johansen <[e-mail]>
Signed-off-by: James Morris <[e-mail]>

security/apparmor/include/policy_unpack.h

···
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor policy loading interface function 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 __POLICY_INTERFACE_H
+#define __POLICY_INTERFACE_H
+
+struct aa_profile *aa_unpack(void *udata, size_t size, const char **ns);
+
+#endif /* __POLICY_INTERFACE_H */

security/apparmor/policy_unpack.c

···
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor functions for unpacking policy loaded from
+ * userspace.
+ *
+ * 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.
+ *
+ * AppArmor uses a serialized binary format for loading policy.
+ * To find policy format documentation look in Documentation/apparmor.txt
+ * All policy is validated before it is used.
+ */
+
+#include <asm/unaligned.h>
+#include <linux/ctype.h>
+#include <linux/errno.h>
+
+#include "include/apparmor.h"
+#include "include/audit.h"
+#include "include/context.h"
+#include "include/match.h"
+#include "include/policy.h"
+#include "include/policy_unpack.h"
+#include "include/sid.h"
+
+/*
+ * The AppArmor interface treats data as a type byte followed by the
+ * actual data.  The interface has the notion of a a named entry
+ * which has a name (AA_NAME typecode followed by name string) followed by
+ * the entries typecode and data.  Named types allow for optional
+ * elements and extensions to be added and tested for without breaking
+ * backwards compatibility.
+ */
+
+enum aa_code {
+	AA_U8,
+	AA_U16,
+	AA_U32,
+	AA_U64,
+	AA_NAME,		/* same as string except it is items name */
+	AA_STRING,
+	AA_BLOB,
+	AA_STRUCT,
+	AA_STRUCTEND,
+	AA_LIST,
+	AA_LISTEND,
+	AA_ARRAY,
+	AA_ARRAYEND,
+};
+
+/*
+ * aa_ext is the read of the buffer containing the serialized profile.  The
+ * data is copied into a kernel buffer in apparmorfs and then handed off to
+ * the unpack routines.
+ */
+struct aa_ext {
+	void *start;
+	void *end;
+	void *pos;		/* pointer to current position in the buffer */
+	u32 version;
+};
+
+/* audit callback for unpack fields */
+static void audit_cb(struct audit_buffer *ab, void *va)
+{
+	struct common_audit_data *sa = va;
+	if (sa->aad.iface.target) {
+		struct aa_profile *name = sa->aad.iface.target;
+		audit_log_format(ab, " name=");
+		audit_log_untrustedstring(ab, name->base.hname);
+	}
+	if (sa->aad.iface.pos)
+		audit_log_format(ab, " offset=%ld", sa->aad.iface.pos);
+}
+
+/**
+ * audit_iface - do audit message for policy unpacking/load/replace/remove
+ * @new: profile if it has been allocated (MAYBE NULL)
+ * @name: name of the profile being manipulated (MAYBE NULL)
+ * @info: any extra info about the failure (MAYBE NULL)
+ * @e: buffer position info (NOT NULL)
+ * @error: error code
+ *
+ * Returns: %0 or error
+ */
+static int audit_iface(struct aa_profile *new, const char *name,
+		       const char *info, struct aa_ext *e, int error)
+{
+	struct aa_profile *profile = __aa_current_profile();
+	struct common_audit_data sa;
+	COMMON_AUDIT_DATA_INIT(&sa, NONE);
+	sa.aad.iface.pos = e->pos - e->start;
+	sa.aad.iface.target = new;
+	sa.aad.name = name;
+	sa.aad.info = info;
+	sa.aad.error = error;
+
+	return aa_audit(AUDIT_APPARMOR_STATUS, profile, GFP_KERNEL, &sa,
+			audit_cb);
+}
+
+/* test if read will be in packed data bounds */
+static bool inbounds(struct aa_ext *e, size_t size)
+{
+	return (size <= e->end - e->pos);
+}
+
+/**
+ * aa_u16_chunck - test and do bounds checking for a u16 size based chunk
+ * @e: serialized data read head (NOT NULL)
+ * @chunk: start address for chunk of data (NOT NULL)
+ *
+ * Returns: the size of chunk found with the read head at the end of the chunk.
+ */
+static size_t unpack_u16_chunk(struct aa_ext *e, char **chunk)
+{
+	size_t size = 0;
+
+	if (!inbounds(e, sizeof(u16)))
+		return 0;
+	size = le16_to_cpu(get_unaligned((u16 *) e->pos));
+	e->pos += sizeof(u16);
+	if (!inbounds(e, size))
+		return 0;
+	*chunk = e->pos;
+	e->pos += size;
+	return size;
+}
+
+/* unpack control byte */
+static bool unpack_X(struct aa_ext *e, enum aa_code code)
+{
+	if (!inbounds(e, 1))
+		return 0;
+	if (*(u8 *) e->pos != code)
+		return 0;
+	e->pos++;
+	return 1;
+}
+
+/**
+ * unpack_nameX - check is the next element is of type X with a name of @name
+ * @e: serialized data extent information  (NOT NULL)
+ * @code: type code
+ * @name: name to match to the serialized element.  (MAYBE NULL)
+ *
+ * check that the next serialized data element is of type X and has a tag
+ * name @name.  If @name is specified then there must be a matching
+ * name element in the stream.  If @name is NULL any name element will be
+ * skipped and only the typecode will be tested.
+ *
+ * Returns 1 on success (both type code and name tests match) and the read
+ * head is advanced past the headers
+ *
+ * Returns: 0 if either match fails, the read head does not move
+ */
+static bool unpack_nameX(struct aa_ext *e, enum aa_code code, const char *name)
+{
+	/*
+	 * May need to reset pos if name or type doesn't match
+	 */
+	void *pos = e->pos;
+	/*
+	 * Check for presence of a tagname, and if present name size
+	 * AA_NAME tag value is a u16.
+	 */
+	if (unpack_X(e, AA_NAME)) {
+		char *tag = NULL;
+		size_t size = unpack_u16_chunk(e, &tag);
+		/* if a name is specified it must match. otherwise skip tag */
+		if (name && (!size || strcmp(name, tag)))
+			goto fail;
+	} else if (name) {
+		/* if a name is specified and there is no name tag fail */
+		goto fail;
+	}
+
+	/* now check if type code matches */
+	if (unpack_X(e, code))
+		return 1;
+
+fail:
+	e->pos = pos;
+	return 0;
+}
+
+static bool unpack_u32(struct aa_ext *e, u32 *data, const char *name)
+{
+	if (unpack_nameX(e, AA_U32, name)) {
+		if (!inbounds(e, sizeof(u32)))
+			return 0;
+		if (data)
+			*data = le32_to_cpu(get_unaligned((u32 *) e->pos));
+		e->pos += sizeof(u32);
+		return 1;
+	}
+	return 0;
+}
+
+static bool unpack_u64(struct aa_ext *e, u64 *data, const char *name)
+{
+	if (unpack_nameX(e, AA_U64, name)) {
+		if (!inbounds(e, sizeof(u64)))
+			return 0;
+		if (data)
+			*data = le64_to_cpu(get_unaligned((u64 *) e->pos));
+		e->pos += sizeof(u64);
+		return 1;
+	}
+	return 0;
+}
+
+static size_t unpack_array(struct aa_ext *e, const char *name)
+{
+	if (unpack_nameX(e, AA_ARRAY, name)) {
+		int size;
+		if (!inbounds(e, sizeof(u16)))
+			return 0;
+		size = (int)le16_to_cpu(get_unaligned((u16 *) e->pos));
+		e->pos += sizeof(u16);
+		return size;
+	}
+	return 0;
+}
+
+static size_t unpack_blob(struct aa_ext *e, char **blob, const char *name)
+{
+	if (unpack_nameX(e, AA_BLOB, name)) {
+		u32 size;
+		if (!inbounds(e, sizeof(u32)))
+			return 0;
+		size = le32_to_cpu(get_unaligned((u32 *) e->pos));
+		e->pos += sizeof(u32);
+		if (inbounds(e, (size_t) size)) {
+			*blob = e->pos;
+			e->pos += size;
+			return size;
+		}
+	}
+	return 0;
+}
+
+static int unpack_str(struct aa_ext *e, const char **string, const char *name)
+{
+	char *src_str;
+	size_t size = 0;
+	void *pos = e->pos;
+	*string = NULL;
+	if (unpack_nameX(e, AA_STRING, name)) {
+		size = unpack_u16_chunk(e, &src_str);
+		if (size) {
+			/* strings are null terminated, length is size - 1 */
+			if (src_str[size - 1] != 0)
+				goto fail;
+			*string = src_str;
+		}
+	}
+	return size;
+
+fail:
+	e->pos = pos;
+	return 0;
+}
+
+static int unpack_strdup(struct aa_ext *e, char **string, const char *name)
+{
+	const char *tmp;
+	void *pos = e->pos;
+	int res = unpack_str(e, &tmp, name);
+	*string = NULL;
+
+	if (!res)
+		return 0;
+
+	*string = kmemdup(tmp, res, GFP_KERNEL);
+	if (!*string) {
+		e->pos = pos;
+		return 0;
+	}
+
+	return res;
+}
+
+/**
+ * verify_accept - verify the accept tables of a dfa
+ * @dfa: dfa to verify accept tables of (NOT NULL)
+ * @flags: flags governing dfa
+ *
+ * Returns: 1 if valid accept tables else 0 if error
+ */
+static bool verify_accept(struct aa_dfa *dfa, int flags)
+{
+	int i;
+
+	/* verify accept permissions */
+	for (i = 0; i < dfa->tables[YYTD_ID_ACCEPT]->td_lolen; i++) {
+		int mode = ACCEPT_TABLE(dfa)[i];
+
+		if (mode & ~DFA_VALID_PERM_MASK)
+			return 0;
+
+		if (ACCEPT_TABLE2(dfa)[i] & ~DFA_VALID_PERM2_MASK)
+			return 0;
+	}
+	return 1;
+}
+
+/**
+ * unpack_dfa - unpack a file rule dfa
+ * @e: serialized data extent information (NOT NULL)
+ *
+ * returns dfa or ERR_PTR or NULL if no dfa
+ */
+static struct aa_dfa *unpack_dfa(struct aa_ext *e)
+{
+	char *blob = NULL;
+	size_t size;
+	struct aa_dfa *dfa = NULL;
+
+	size = unpack_blob(e, &blob, "aadfa");
+	if (size) {
+		/*
+		 * The dfa is aligned with in the blob to 8 bytes
+		 * from the beginning of the stream.
+		 */
+		size_t sz = blob - (char *)e->start;
+		size_t pad = ALIGN(sz, 8) - sz;
+		int flags = TO_ACCEPT1_FLAG(YYTD_DATA32) |
+			TO_ACCEPT2_FLAG(YYTD_DATA32);
+
+
+		if (aa_g_paranoid_load)
+			flags |= DFA_FLAG_VERIFY_STATES;
+
+		dfa = aa_dfa_unpack(blob + pad, size - pad, flags);
+
+		if (IS_ERR(dfa))
+			return dfa;
+
+		if (!verify_accept(dfa, flags))
+			goto fail;
+	}
+
+	return dfa;
+
+fail:
+	aa_put_dfa(dfa);
+	return ERR_PTR(-EPROTO);
+}
+
+/**
+ * unpack_trans_table - unpack a profile transition table
+ * @e: serialized data extent information  (NOT NULL)
+ * @profile: profile to add the accept table to (NOT NULL)
+ *
+ * Returns: 1 if table succesfully unpacked
+ */
+static bool unpack_trans_table(struct aa_ext *e, struct aa_profile *profile)
+{
+	void *pos = e->pos;
+
+	/* exec table is optional */
+	if (unpack_nameX(e, AA_STRUCT, "xtable")) {
+		int i, size;
+
+		size = unpack_array(e, NULL);
+		/* currently 4 exec bits and entries 0-3 are reserved iupcx */
+		if (size > 16 - 4)
+			goto fail;
+		profile->file.trans.table = kzalloc(sizeof(char *) * size,
+						    GFP_KERNEL);
+		if (!profile->file.trans.table)
+			goto fail;
+
+		profile->file.trans.size = size;
+		for (i = 0; i < size; i++) {
+			char *str;
+			int c, j, size = unpack_strdup(e, &str, NULL);
+			/* unpack_strdup verifies that the last character is
+			 * null termination byte.
+			 */
+			if (!size)
+				goto fail;
+			profile->file.trans.table[i] = str;
+			/* verify that name doesn't start with space */
+			if (isspace(*str))
+				goto fail;
+
+			/* count internal #  of internal \0 */
+			for (c = j = 0; j < size - 2; j++) {
+				if (!str[j])
+					c++;
+			}
+			if (*str == ':') {
+				/* beginning with : requires an embedded \0,
+				 * verify that exactly 1 internal \0 exists
+				 * trailing \0 already verified by unpack_strdup
+				 */
+				if (c != 1)
+					goto fail;
+				/* first character after : must be valid */
+				if (!str[1])
+					goto fail;
+			} else if (c)
+				/* fail - all other cases with embedded \0 */
+				goto fail;
+		}
+		if (!unpack_nameX(e, AA_ARRAYEND, NULL))
+			goto fail;
+		if (!unpack_nameX(e, AA_STRUCTEND, NULL))
+			goto fail;
+	}
+	return 1;
+
+fail:
+	aa_free_domain_entries(&profile->file.trans);
+	e->pos = pos;
+	return 0;
+}
+
+static bool unpack_rlimits(struct aa_ext *e, struct aa_profile *profile)
+{
+	void *pos = e->pos;
+
+	/* rlimits are optional */
+	if (unpack_nameX(e, AA_STRUCT, "rlimits")) {
+		int i, size;
+		u32 tmp = 0;
+		if (!unpack_u32(e, &tmp, NULL))
+			goto fail;
+		profile->rlimits.mask = tmp;
+
+		size = unpack_array(e, NULL);
+		if (size > RLIM_NLIMITS)
+			goto fail;
+		for (i = 0; i < size; i++) {
+			u64 tmp = 0;
+			int a = aa_map_resource(i);
+			if (!unpack_u64(e, &tmp, NULL))
+				goto fail;
+			profile->rlimits.limits[a].rlim_max = tmp;
+		}
+		if (!unpack_nameX(e, AA_ARRAYEND, NULL))
+			goto fail;
+		if (!unpack_nameX(e, AA_STRUCTEND, NULL))
+			goto fail;
+	}
+	return 1;
+
+fail:
+	e->pos = pos;
+	return 0;
+}
+
+/**
+ * unpack_profile - unpack a serialized profile
+ * @e: serialized data extent information (NOT NULL)
+ *
+ * NOTE: unpack profile sets audit struct if there is a failure
+ */
+static struct aa_profile *unpack_profile(struct aa_ext *e)
+{
+	struct aa_profile *profile = NULL;
+	const char *name = NULL;
+	int error = -EPROTO;
+	kernel_cap_t tmpcap;
+	u32 tmp;
+
+	/* check that we have the right struct being passed */
+	if (!unpack_nameX(e, AA_STRUCT, "profile"))
+		goto fail;
+	if (!unpack_str(e, &name, NULL))
+		goto fail;
+
+	profile = aa_alloc_profile(name);
+	if (!profile)
+		return ERR_PTR(-ENOMEM);
+
+	/* profile renaming is optional */
+	(void) unpack_str(e, &profile->rename, "rename");
+
+	/* xmatch is optional and may be NULL */
+	profile->xmatch = unpack_dfa(e);
+	if (IS_ERR(profile->xmatch)) {
+		error = PTR_ERR(profile->xmatch);
+		profile->xmatch = NULL;
+		goto fail;
+	}
+	/* xmatch_len is not optional if xmatch is set */
+	if (profile->xmatch) {
+		if (!unpack_u32(e, &tmp, NULL))
+			goto fail;
+		profile->xmatch_len = tmp;
+	}
+
+	/* per profile debug flags (complain, audit) */
+	if (!unpack_nameX(e, AA_STRUCT, "flags"))
+		goto fail;
+	if (!unpack_u32(e, &tmp, NULL))
+		goto fail;
+	if (tmp)
+		profile->flags |= PFLAG_HAT;
+	if (!unpack_u32(e, &tmp, NULL))
+		goto fail;
+	if (tmp)
+		profile->mode = APPARMOR_COMPLAIN;
+	if (!unpack_u32(e, &tmp, NULL))
+		goto fail;
+	if (tmp)
+		profile->audit = AUDIT_ALL;
+
+	if (!unpack_nameX(e, AA_STRUCTEND, NULL))
+		goto fail;
+
+	/* path_flags is optional */
+	if (unpack_u32(e, &profile->path_flags, "path_flags"))
+		profile->path_flags |= profile->flags & PFLAG_MEDIATE_DELETED;
+	else
+		/* set a default value if path_flags field is not present */
+		profile->path_flags = PFLAG_MEDIATE_DELETED;
+
+	if (!unpack_u32(e, &(profile->caps.allow.cap[0]), NULL))
+		goto fail;
+	if (!unpack_u32(e, &(profile->caps.audit.cap[0]), NULL))
+		goto fail;
+	if (!unpack_u32(e, &(profile->caps.quiet.cap[0]), NULL))
+		goto fail;
+	if (!unpack_u32(e, &tmpcap.cap[0], NULL))
+		goto fail;
+
+	if (unpack_nameX(e, AA_STRUCT, "caps64")) {
+		/* optional upper half of 64 bit caps */
+		if (!unpack_u32(e, &(profile->caps.allow.cap[1]), NULL))
+			goto fail;
+		if (!unpack_u32(e, &(profile->caps.audit.cap[1]), NULL))
+			goto fail;
+		if (!unpack_u32(e, &(profile->caps.quiet.cap[1]), NULL))
+			goto fail;
+		if (!unpack_u32(e, &(tmpcap.cap[1]), NULL))
+			goto fail;
+		if (!unpack_nameX(e, AA_STRUCTEND, NULL))
+			goto fail;
+	}
+
+	if (unpack_nameX(e, AA_STRUCT, "capsx")) {
+		/* optional extended caps mediation mask */
+		if (!unpack_u32(e, &(profile->caps.extended.cap[0]), NULL))
+			goto fail;
+		if (!unpack_u32(e, &(profile->caps.extended.cap[1]), NULL))
+			goto fail;
+	}
+
+	if (!unpack_rlimits(e, profile))
+		goto fail;
+
+	/* get file rules */
+	profile->file.dfa = unpack_dfa(e);
+	if (IS_ERR(profile->file.dfa)) {
+		error = PTR_ERR(profile->file.dfa);
+		profile->file.dfa = NULL;
+		goto fail;
+	}
+
+	if (!unpack_u32(e, &profile->file.start, "dfa_start"))
+		/* default start state */
+		profile->file.start = DFA_START;
+
+	if (!unpack_trans_table(e, profile))
+		goto fail;
+
+	if (!unpack_nameX(e, AA_STRUCTEND, NULL))
+		goto fail;
+
+	return profile;
+
+fail:
+	if (profile)
+		name = NULL;
+	else if (!name)
+		name = "unknown";
+	audit_iface(profile, name, "failed to unpack profile", e, error);
+	aa_put_profile(profile);
+
+	return ERR_PTR(error);
+}
+
+/**
+ * verify_head - unpack serialized stream header
+ * @e: serialized data read head (NOT NULL)
+ * @ns: Returns - namespace if one is specified else NULL (NOT NULL)
+ *
+ * Returns: error or 0 if header is good
+ */
+static int verify_header(struct aa_ext *e, const char **ns)
+{
+	int error = -EPROTONOSUPPORT;
+	/* get the interface version */
+	if (!unpack_u32(e, &e->version, "version")) {
+		audit_iface(NULL, NULL, "invalid profile format", e, error);
+		return error;
+	}
+
+	/* check that the interface version is currently supported */
+	if (e->version != 5) {
+		audit_iface(NULL, NULL, "unsupported interface version", e,
+			    error);
+		return error;
+	}
+
+	/* read the namespace if present */
+	if (!unpack_str(e, ns, "namespace"))
+		*ns = NULL;
+
+	return 0;
+}
+
+static bool verify_xindex(int xindex, int table_size)
+{
+	int index, xtype;
+	xtype = xindex & AA_X_TYPE_MASK;
+	index = xindex & AA_X_INDEX_MASK;
+	if (xtype == AA_X_TABLE && index > table_size)
+		return 0;
+	return 1;
+}
+
+/* verify dfa xindexes are in range of transition tables */
+static bool verify_dfa_xindex(struct aa_dfa *dfa, int table_size)
+{
+	int i;
+	for (i = 0; i < dfa->tables[YYTD_ID_ACCEPT]->td_lolen; i++) {
+		if (!verify_xindex(dfa_user_xindex(dfa, i), table_size))
+			return 0;
+		if (!verify_xindex(dfa_other_xindex(dfa, i), table_size))
+			return 0;
+	}
+	return 1;
+}
+
+/**
+ * verify_profile - Do post unpack analysis to verify profile consistency
+ * @profile: profile to verify (NOT NULL)
+ *
+ * Returns: 0 if passes verification else error
+ */
+static int verify_profile(struct aa_profile *profile)
+{
+	if (aa_g_paranoid_load) {
+		if (profile->file.dfa &&
+		    !verify_dfa_xindex(profile->file.dfa,
+				       profile->file.trans.size)) {
+			audit_iface(profile, NULL, "Invalid named transition",
+				    NULL, -EPROTO);
+			return -EPROTO;
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * aa_unpack - unpack packed binary profile data loaded from user space
+ * @udata: user data copied to kmem  (NOT NULL)
+ * @size: the size of the user data
+ * @ns: Returns namespace profile is in if specified else NULL (NOT NULL)
+ *
+ * Unpack user data and return refcounted allocated profile or ERR_PTR
+ *
+ * Returns: profile else error pointer if fails to unpack
+ */
+struct aa_profile *aa_unpack(void *udata, size_t size, const char **ns)
+{
+	struct aa_profile *profile = NULL;
+	int error;
+	struct aa_ext e = {
+		.start = udata,
+		.end = udata + size,
+		.pos = udata,
+	};
+
+	error = verify_header(&e, ns);
+	if (error)
+		return ERR_PTR(error);
+
+	profile = unpack_profile(&e);
+	if (IS_ERR(profile))
+		return profile;
+
+	error = verify_profile(profile);
+	if (error) {
+		aa_put_profile(profile);
+		profile = ERR_PTR(error);
+	}
+
+	/* return refcount */
+	return profile;
+}