TOMOYO: Add description of lists and structures.

This patch adds some descriptions of lists and structures.
This patch contains no code changes.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>

6 files changed, 504 insertions, 34 deletions

diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index a44f655..fdd1f4b 100644
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -28,7 +28,13 @@ static const char *tomoyo_mode_2[4] = {
 	"disabled", "enabled", "enabled", "enabled"
 };
 
-/* Table for profile. */
+/*
+ * tomoyo_control_array is a static data which contains
+ *
+ *  (1) functionality name used by /sys/kernel/security/tomoyo/profile .
+ *  (2) initial values for "struct tomoyo_profile".
+ *  (3) max values for "struct tomoyo_profile".
+ */
 static struct {
 	const char *keyword;
 	unsigned int current_value;
@@ -39,7 +45,13 @@ static struct {
 	[TOMOYO_VERBOSE]          = { "TOMOYO_VERBOSE",      1,       1 },
 };
 
-/* Profile table. Memory is allocated as needed. */
+/*
+ * tomoyo_profile is a structure which is used for holding the mode of access
+ * controls. TOMOYO has 4 modes: disabled, learning, permissive, enforcing.
+ * An administrator can define up to 256 profiles.
+ * The ->profile of "struct tomoyo_domain_info" is used for remembering
+ * the profile's number (0 - 255) assigned to that domain.
+ */
 static struct tomoyo_profile {
 	unsigned int value[TOMOYO_MAX_CONTROL_INDEX];
 	const struct tomoyo_path_info *comment;
@@ -1006,7 +1018,19 @@ static int tomoyo_read_profile(struct tomoyo_io_buffer *head)
 	return 0;
 }
 
-/* Structure for policy manager. */
+/*
+ * tomoyo_policy_manager_entry is a structure which is used for holding list of
+ * domainnames or programs which are permitted to modify configuration via
+ * /sys/kernel/security/tomoyo/ interface.
+ * It has following fields.
+ *
+ *  (1) "list" which is linked to tomoyo_policy_manager_list .
+ *  (2) "manager" is a domainname or a program's pathname.
+ *  (3) "is_domain" is a bool which is true if "manager" is a domainname, false
+ *      otherwise.
+ *  (4) "is_deleted" is a bool which is true if marked as deleted, false
+ *      otherwise.
+ */
 struct tomoyo_policy_manager_entry {
 	struct list_head list;
 	/* A path to program or a domainname. */
@@ -1015,7 +1039,36 @@ struct tomoyo_policy_manager_entry {
 	bool is_deleted; /* True if this entry is deleted. */
 };
 
-/* The list for "struct tomoyo_policy_manager_entry". */
+/*
+ * tomoyo_policy_manager_list is used for holding list of domainnames or
+ * programs which are permitted to modify configuration via
+ * /sys/kernel/security/tomoyo/ interface.
+ *
+ * An entry is added by
+ *
+ * # echo '<kernel> /sbin/mingetty /bin/login /bin/bash' > \
+ *                                        /sys/kernel/security/tomoyo/manager
+ *  (if you want to specify by a domainname)
+ *
+ *  or
+ *
+ * # echo '/usr/lib/ccs/editpolicy' > /sys/kernel/security/tomoyo/manager
+ *  (if you want to specify by a program's location)
+ *
+ * and is deleted by
+ *
+ * # echo 'delete <kernel> /sbin/mingetty /bin/login /bin/bash' > \
+ *                                        /sys/kernel/security/tomoyo/manager
+ *
+ *  or
+ *
+ * # echo 'delete /usr/lib/ccs/editpolicy' > \
+ *                                        /sys/kernel/security/tomoyo/manager
+ *
+ * and all entries are retrieved by
+ *
+ * # cat /sys/kernel/security/tomoyo/manager
+ */
 static LIST_HEAD(tomoyo_policy_manager_list);
 static DECLARE_RWSEM(tomoyo_policy_manager_list_lock);
 
@@ -2124,7 +2177,13 @@ static ssize_t tomoyo_write(struct file *file, const char __user *buf,
 	return tomoyo_write_control(file, buf, count);
 }
 
-/* Operations for /sys/kernel/security/tomoyo/ interface. */
+/*
+ * tomoyo_operations is a "struct file_operations" which is used for handling
+ * /sys/kernel/security/tomoyo/ interface.
+ *
+ * Some files under /sys/kernel/security/tomoyo/ directory accept open(O_RDWR).
+ * See tomoyo_io_buffer for internals.
+ */
 static const struct file_operations tomoyo_operations = {
 	.open    = tomoyo_open,
 	.release = tomoyo_release,
diff --git a/security/tomoyo/common.h b/security/tomoyo/common.h
index d8b9504..6d6ba09 100644
--- a/security/tomoyo/common.h
+++ b/security/tomoyo/common.h
@@ -26,12 +26,40 @@
 struct dentry;
 struct vfsmount;
 
-/* Temporary buffer for holding pathnames. */
+/*
+ * tomoyo_page_buffer is a structure which is used for holding a pathname
+ * obtained from "struct dentry" and "struct vfsmount" pair.
+ * As of now, it is 4096 bytes. If users complain that 4096 bytes is too small
+ * (because TOMOYO escapes non ASCII printable characters using \ooo format),
+ * we will make the buffer larger.
+ */
 struct tomoyo_page_buffer {
 	char buffer[4096];
 };
 
-/* Structure for holding a token. */
+/*
+ * tomoyo_path_info is a structure which is used for holding a string data
+ * used by TOMOYO.
+ * This structure has several fields for supporting pattern matching.
+ *
+ * (1) "name" is the '\0' terminated string data.
+ * (2) "hash" is full_name_hash(name, strlen(name)).
+ *     This allows tomoyo_pathcmp() to compare by hash before actually compare
+ *     using strcmp().
+ * (3) "const_len" is the length of the initial segment of "name" which
+ *     consists entirely of non wildcard characters. In other words, the length
+ *     which we can compare two strings using strncmp().
+ * (4) "is_dir" is a bool which is true if "name" ends with "/",
+ *     false otherwise.
+ *     TOMOYO distinguishes directory and non-directory. A directory ends with
+ *     "/" and non-directory does not end with "/".
+ * (5) "is_patterned" is a bool which is true if "name" contains wildcard
+ *     characters, false otherwise. This allows TOMOYO to use "hash" and
+ *     strcmp() for string comparison if "is_patterned" is false.
+ * (6) "depth" is calculated using the number of "/" characters in "name".
+ *     This allows TOMOYO to avoid comparing two pathnames which never match
+ *     (e.g. whether "/var/www/html/index.html" matches "/tmp/sh-thd-\$").
+ */
 struct tomoyo_path_info {
 	const char *name;
 	u32 hash;          /* = full_name_hash(name, strlen(name)) */
@@ -50,7 +78,20 @@ struct tomoyo_path_info {
  */
 #define TOMOYO_MAX_PATHNAME_LEN 4000
 
-/* Structure for holding requested pathname. */
+/*
+ * tomoyo_path_info_with_data is a structure which is used for holding a
+ * pathname obtained from "struct dentry" and "struct vfsmount" pair.
+ *
+ * "struct tomoyo_path_info_with_data" consists of "struct tomoyo_path_info"
+ * and buffer for the pathname, while "struct tomoyo_page_buffer" consists of
+ * buffer for the pathname only.
+ *
+ * "struct tomoyo_path_info_with_data" is intended to allow TOMOYO to release
+ * both "struct tomoyo_path_info" and buffer for the pathname by single kfree()
+ * so that we don't need to return two pointers to the caller. If the caller
+ * puts "struct tomoyo_path_info" on stack memory, we will be able to remove
+ * "struct tomoyo_path_info_with_data".
+ */
 struct tomoyo_path_info_with_data {
 	/* Keep "head" first, for this pointer is passed to tomoyo_free(). */
 	struct tomoyo_path_info head;
@@ -60,7 +101,15 @@ struct tomoyo_path_info_with_data {
 };
 
 /*
- * Common header for holding ACL entries.
+ * tomoyo_acl_info is a structure which is used for holding
+ *
+ *  (1) "list" which is linked to the ->acl_info_list of
+ *      "struct tomoyo_domain_info"
+ *  (2) "type" which tells
+ *      (a) type & 0x7F : type of the entry (either
+ *          "struct tomoyo_single_path_acl_record" or
+ *          "struct tomoyo_double_path_acl_record")
+ *      (b) type & 0x80 : whether the entry is marked as "deleted".
  *
  * Packing "struct tomoyo_acl_info" allows
  * "struct tomoyo_single_path_acl_record" to embed "u16" and
@@ -80,7 +129,28 @@ struct tomoyo_acl_info {
 /* This ACL entry is deleted.           */
 #define TOMOYO_ACL_DELETED        0x80
 
-/* Structure for domain information. */
+/*
+ * tomoyo_domain_info is a structure which is used for holding permissions
+ * (e.g. "allow_read /lib/libc-2.5.so") given to each domain.
+ * It has following fields.
+ *
+ *  (1) "list" which is linked to tomoyo_domain_list .
+ *  (2) "acl_info_list" which is linked to "struct tomoyo_acl_info".
+ *  (3) "domainname" which holds the name of the domain.
+ *  (4) "profile" which remembers profile number assigned to this domain.
+ *  (5) "is_deleted" is a bool which is true if this domain is marked as
+ *      "deleted", false otherwise.
+ *  (6) "quota_warned" is a bool which is used for suppressing warning message
+ *      when learning mode learned too much entries.
+ *  (7) "flags" which remembers this domain's attributes.
+ *
+ * A domain's lifecycle is an analogy of files on / directory.
+ * Multiple domains with the same domainname cannot be created (as with
+ * creating files with the same filename fails with -EEXIST).
+ * If a process reached a domain, that process can reside in that domain after
+ * that domain is marked as "deleted" (as with a process can access an already
+ * open()ed file after that file was unlink()ed).
+ */
 struct tomoyo_domain_info {
 	struct list_head list;
 	struct list_head acl_info_list;
@@ -107,10 +177,18 @@ struct tomoyo_domain_info {
 #define TOMOYO_DOMAIN_FLAGS_TRANSITION_FAILED        2
 
 /*
- * Structure for "allow_read/write", "allow_execute", "allow_read",
- * "allow_write", "allow_create", "allow_unlink", "allow_mkdir", "allow_rmdir",
- * "allow_mkfifo", "allow_mksock", "allow_mkblock", "allow_mkchar",
- * "allow_truncate", "allow_symlink" and "allow_rewrite" directive.
+ * tomoyo_single_path_acl_record is a structure which is used for holding an
+ * entry with one pathname operation (e.g. open(), mkdir()).
+ * It has following fields.
+ *
+ *  (1) "head" which is a "struct tomoyo_acl_info".
+ *  (2) "perm" which is a bitmask of permitted operations.
+ *  (3) "filename" is the pathname.
+ *
+ * Directives held by this structure are "allow_read/write", "allow_execute",
+ * "allow_read", "allow_write", "allow_create", "allow_unlink", "allow_mkdir",
+ * "allow_rmdir", "allow_mkfifo", "allow_mksock", "allow_mkblock",
+ * "allow_mkchar", "allow_truncate", "allow_symlink" and "allow_rewrite".
  */
 struct tomoyo_single_path_acl_record {
 	struct tomoyo_acl_info head; /* type = TOMOYO_TYPE_SINGLE_PATH_ACL */
@@ -119,7 +197,18 @@ struct tomoyo_single_path_acl_record {
 	const struct tomoyo_path_info *filename;
 };
 
-/* Structure for "allow_rename" and "allow_link" directive. */
+/*
+ * tomoyo_double_path_acl_record is a structure which is used for holding an
+ * entry with two pathnames operation (i.e. link() and rename()).
+ * It has following fields.
+ *
+ *  (1) "head" which is a "struct tomoyo_acl_info".
+ *  (2) "perm" which is a bitmask of permitted operations.
+ *  (3) "filename1" is the source/old pathname.
+ *  (4) "filename2" is the destination/new pathname.
+ *
+ * Directives held by this structure are "allow_rename" and "allow_link".
+ */
 struct tomoyo_double_path_acl_record {
 	struct tomoyo_acl_info head; /* type = TOMOYO_TYPE_DOUBLE_PATH_ACL */
 	u8 perm;
@@ -152,7 +241,29 @@ struct tomoyo_double_path_acl_record {
 #define TOMOYO_VERBOSE                       2
 #define TOMOYO_MAX_CONTROL_INDEX             3
 
-/* Structure for reading/writing policy via securityfs interfaces. */
+/*
+ * tomoyo_io_buffer is a structure which is used for reading and modifying
+ * configuration via /sys/kernel/security/tomoyo/ interface.
+ * It has many fields. ->read_var1 , ->read_var2 , ->write_var1 are used as
+ * cursors.
+ *
+ * Since the content of /sys/kernel/security/tomoyo/domain_policy is a list of
+ * "struct tomoyo_domain_info" entries and each "struct tomoyo_domain_info"
+ * entry has a list of "struct tomoyo_acl_info", we need two cursors when
+ * reading (one is for traversing tomoyo_domain_list and the other is for
+ * traversing "struct tomoyo_acl_info"->acl_info_list ).
+ *
+ * If a line written to /sys/kernel/security/tomoyo/domain_policy starts with
+ * "select ", TOMOYO seeks the cursor ->read_var1 and ->write_var1 to the
+ * domain with the domainname specified by the rest of that line (NULL is set
+ * if seek failed).
+ * If a line written to /sys/kernel/security/tomoyo/domain_policy starts with
+ * "delete ", TOMOYO deletes an entry or a domain specified by the rest of that
+ * line (->write_var1 is set to NULL if a domain was deleted).
+ * If a line written to /sys/kernel/security/tomoyo/domain_policy starts with
+ * neither "select " nor "delete ", an entry or a domain specified by that line
+ * is appended.
+ */
 struct tomoyo_io_buffer {
 	int (*read) (struct tomoyo_io_buffer *);
 	int (*write) (struct tomoyo_io_buffer *);
diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index eb75401..1d8b169 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -19,11 +19,63 @@
 /* The initial domain. */
 struct tomoyo_domain_info tomoyo_kernel_domain;
 
-/* The list for "struct tomoyo_domain_info". */
+/*
+ * tomoyo_domain_list is used for holding list of domains.
+ * The ->acl_info_list of "struct tomoyo_domain_info" is used for holding
+ * permissions (e.g. "allow_read /lib/libc-2.5.so") given to each domain.
+ *
+ * An entry is added by
+ *
+ * # ( echo "<kernel>"; echo "allow_execute /sbin/init" ) > \
+ *                                  /sys/kernel/security/tomoyo/domain_policy
+ *
+ * and is deleted by
+ *
+ * # ( echo "<kernel>"; echo "delete allow_execute /sbin/init" ) > \
+ *                                  /sys/kernel/security/tomoyo/domain_policy
+ *
+ * and all entries are retrieved by
+ *
+ * # cat /sys/kernel/security/tomoyo/domain_policy
+ *
+ * A domain is added by
+ *
+ * # echo "<kernel>" > /sys/kernel/security/tomoyo/domain_policy
+ *
+ * and is deleted by
+ *
+ * # echo "delete <kernel>" > /sys/kernel/security/tomoyo/domain_policy
+ *
+ * and all domains are retrieved by
+ *
+ * # grep '^<kernel>' /sys/kernel/security/tomoyo/domain_policy
+ *
+ * Normally, a domainname is monotonically getting longer because a domainname
+ * which the process will belong to if an execve() operation succeeds is
+ * defined as a concatenation of "current domainname" + "pathname passed to
+ * execve()".
+ * See tomoyo_domain_initializer_list and tomoyo_domain_keeper_list for
+ * exceptions.
+ */
 LIST_HEAD(tomoyo_domain_list);
 DECLARE_RWSEM(tomoyo_domain_list_lock);
 
-/* Structure for "initialize_domain" and "no_initialize_domain" keyword. */
+/*
+ * tomoyo_domain_initializer_entry is a structure which is used for holding
+ * "initialize_domain" and "no_initialize_domain" entries.
+ * It has following fields.
+ *
+ *  (1) "list" which is linked to tomoyo_domain_initializer_list .
+ *  (2) "domainname" which is "a domainname" or "the last component of a
+ *      domainname". This field is NULL if "from" clause is not specified.
+ *  (3) "program" which is a program's pathname.
+ *  (4) "is_deleted" is a bool which is true if marked as deleted, false
+ *      otherwise.
+ *  (5) "is_not" is a bool which is true if "no_initialize_domain", false
+ *      otherwise.
+ *  (6) "is_last_name" is a bool which is true if "domainname" is "the last
+ *      component of a domainname", false otherwise.
+ */
 struct tomoyo_domain_initializer_entry {
 	struct list_head list;
 	const struct tomoyo_path_info *domainname;    /* This may be NULL */
@@ -34,7 +86,23 @@ struct tomoyo_domain_initializer_entry {
 	bool is_last_name;
 };
 
-/* Structure for "keep_domain" and "no_keep_domain" keyword. */
+/*
+ * tomoyo_domain_keeper_entry is a structure which is used for holding
+ * "keep_domain" and "no_keep_domain" entries.
+ * It has following fields.
+ *
+ *  (1) "list" which is linked to tomoyo_domain_keeper_list .
+ *  (2) "domainname" which is "a domainname" or "the last component of a
+ *      domainname".
+ *  (3) "program" which is a program's pathname.
+ *      This field is NULL if "from" clause is not specified.
+ *  (4) "is_deleted" is a bool which is true if marked as deleted, false
+ *      otherwise.
+ *  (5) "is_not" is a bool which is true if "no_initialize_domain", false
+ *      otherwise.
+ *  (6) "is_last_name" is a bool which is true if "domainname" is "the last
+ *      component of a domainname", false otherwise.
+ */
 struct tomoyo_domain_keeper_entry {
 	struct list_head list;
 	const struct tomoyo_path_info *domainname;
@@ -45,7 +113,16 @@ struct tomoyo_domain_keeper_entry {
 	bool is_last_name;
 };
 
-/* Structure for "alias" keyword. */
+/*
+ * tomoyo_alias_entry is a structure which is used for holding "alias" entries.
+ * It has following fields.
+ *
+ *  (1) "list" which is linked to tomoyo_alias_list .
+ *  (2) "original_name" which is a dereferenced pathname.
+ *  (3) "aliased_name" which is a symlink's pathname.
+ *  (4) "is_deleted" is a bool which is true if marked as deleted, false
+ *      otherwise.
+ */
 struct tomoyo_alias_entry {
 	struct list_head list;
 	const struct tomoyo_path_info *original_name;
@@ -92,7 +169,42 @@ const char *tomoyo_get_last_name(const struct tomoyo_domain_info *domain)
 	return cp0;
 }
 
-/* The list for "struct tomoyo_domain_initializer_entry". */
+/*
+ * tomoyo_domain_initializer_list is used for holding list of programs which
+ * triggers reinitialization of domainname. Normally, a domainname is
+ * monotonically getting longer. But sometimes, we restart daemon programs.
+ * It would be convenient for us that "a daemon started upon system boot" and
+ * "the daemon restarted from console" belong to the same domain. Thus, TOMOYO
+ * provides a way to shorten domainnames.
+ *
+ * An entry is added by
+ *
+ * # echo 'initialize_domain /usr/sbin/httpd' > \
+ *                               /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and is deleted by
+ *
+ * # echo 'delete initialize_domain /usr/sbin/httpd' > \
+ *                               /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and all entries are retrieved by
+ *
+ * # grep ^initialize_domain /sys/kernel/security/tomoyo/exception_policy
+ *
+ * In the example above, /usr/sbin/httpd will belong to
+ * "<kernel> /usr/sbin/httpd" domain.
+ *
+ * You may specify a domainname using "from" keyword.
+ * "initialize_domain /usr/sbin/httpd from <kernel> /etc/rc.d/init.d/httpd"
+ * will cause "/usr/sbin/httpd" executed from "<kernel> /etc/rc.d/init.d/httpd"
+ * domain to belong to "<kernel> /usr/sbin/httpd" domain.
+ *
+ * You may add "no_" prefix to "initialize_domain".
+ * "initialize_domain /usr/sbin/httpd" and
+ * "no_initialize_domain /usr/sbin/httpd from <kernel> /etc/rc.d/init.d/httpd"
+ * will cause "/usr/sbin/httpd" to belong to "<kernel> /usr/sbin/httpd" domain
+ * unless executed from "<kernel> /etc/rc.d/init.d/httpd" domain.
+ */
 static LIST_HEAD(tomoyo_domain_initializer_list);
 static DECLARE_RWSEM(tomoyo_domain_initializer_list_lock);
 
@@ -268,7 +380,44 @@ static bool tomoyo_is_domain_initializer(const struct tomoyo_path_info *
 	return flag;
 }
 
-/* The list for "struct tomoyo_domain_keeper_entry". */
+/*
+ * tomoyo_domain_keeper_list is used for holding list of domainnames which
+ * suppresses domain transition. Normally, a domainname is monotonically
+ * getting longer. But sometimes, we want to suppress domain transition.
+ * It would be convenient for us that programs executed from a login session
+ * belong to the same domain. Thus, TOMOYO provides a way to suppress domain
+ * transition.
+ *
+ * An entry is added by
+ *
+ * # echo 'keep_domain <kernel> /usr/sbin/sshd /bin/bash' > \
+ *                              /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and is deleted by
+ *
+ * # echo 'delete keep_domain <kernel> /usr/sbin/sshd /bin/bash' > \
+ *                              /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and all entries are retrieved by
+ *
+ * # grep ^keep_domain /sys/kernel/security/tomoyo/exception_policy
+ *
+ * In the example above, any process which belongs to
+ * "<kernel> /usr/sbin/sshd /bin/bash" domain will remain in that domain,
+ * unless explicitly specified by "initialize_domain" or "no_keep_domain".
+ *
+ * You may specify a program using "from" keyword.
+ * "keep_domain /bin/pwd from <kernel> /usr/sbin/sshd /bin/bash"
+ * will cause "/bin/pwd" executed from "<kernel> /usr/sbin/sshd /bin/bash"
+ * domain to remain in "<kernel> /usr/sbin/sshd /bin/bash" domain.
+ *
+ * You may add "no_" prefix to "keep_domain".
+ * "keep_domain <kernel> /usr/sbin/sshd /bin/bash" and
+ * "no_keep_domain /usr/bin/passwd from <kernel> /usr/sbin/sshd /bin/bash" will
+ * cause "/usr/bin/passwd" to belong to
+ * "<kernel> /usr/sbin/sshd /bin/bash /usr/bin/passwd" domain, unless
+ * explicitly specified by "initialize_domain".
+ */
 static LIST_HEAD(tomoyo_domain_keeper_list);
 static DECLARE_RWSEM(tomoyo_domain_keeper_list_lock);
 
@@ -437,7 +586,36 @@ static bool tomoyo_is_domain_keeper(const struct tomoyo_path_info *domainname,
 	return flag;
 }
 
-/* The list for "struct tomoyo_alias_entry". */
+/*
+ * tomoyo_alias_list is used for holding list of symlink's pathnames which are
+ * allowed to be passed to an execve() request. Normally, the domainname which
+ * the current process will belong to after execve() succeeds is calculated
+ * using dereferenced pathnames. But some programs behave differently depending
+ * on the name passed to argv[0]. For busybox, calculating domainname using
+ * dereferenced pathnames will cause all programs in the busybox to belong to
+ * the same domain. Thus, TOMOYO provides a way to allow use of symlink's
+ * pathname for checking execve()'s permission and calculating domainname which
+ * the current process will belong to after execve() succeeds.
+ *
+ * An entry is added by
+ *
+ * # echo 'alias /bin/busybox /bin/cat' > \
+ *                            /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and is deleted by
+ *
+ * # echo 'delete alias /bin/busybox /bin/cat' > \
+ *                            /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and all entries are retrieved by
+ *
+ * # grep ^alias /sys/kernel/security/tomoyo/exception_policy
+ *
+ * In the example above, if /bin/cat is a symlink to /bin/busybox and execution
+ * of /bin/cat is requested, permission is checked for /bin/cat rather than
+ * /bin/busybox and domainname which the current process will belong to after
+ * execve() succeeds is calculated using /bin/cat rather than /bin/busybox .
+ */
 static LIST_HEAD(tomoyo_alias_list);
 static DECLARE_RWSEM(tomoyo_alias_list_lock);
 
diff --git a/security/tomoyo/file.c b/security/tomoyo/file.c
index ab0cd35..5ae3a57 100644
--- a/security/tomoyo/file.c
+++ b/security/tomoyo/file.c
@@ -14,21 +14,50 @@
 #include "realpath.h"
 #define ACC_MODE(x) ("\000\004\002\006"[(x)&O_ACCMODE])
 
-/* Structure for "allow_read" keyword. */
+/*
+ * tomoyo_globally_readable_file_entry is a structure which is used for holding
+ * "allow_read" entries.
+ * It has following fields.
+ *
+ *  (1) "list" which is linked to tomoyo_globally_readable_list .
+ *  (2) "filename" is a pathname which is allowed to open(O_RDONLY).
+ *  (3) "is_deleted" is a bool which is true if marked as deleted, false
+ *      otherwise.
+ */
 struct tomoyo_globally_readable_file_entry {
 	struct list_head list;
 	const struct tomoyo_path_info *filename;
 	bool is_deleted;
 };
 
-/* Structure for "file_pattern" keyword. */
+/*
+ * tomoyo_pattern_entry is a structure which is used for holding
+ * "tomoyo_pattern_list" entries.
+ * It has following fields.
+ *
+ *  (1) "list" which is linked to tomoyo_pattern_list .
+ *  (2) "pattern" is a pathname pattern which is used for converting pathnames
+ *      to pathname patterns during learning mode.
+ *  (3) "is_deleted" is a bool which is true if marked as deleted, false
+ *      otherwise.
+ */
 struct tomoyo_pattern_entry {
 	struct list_head list;
 	const struct tomoyo_path_info *pattern;
 	bool is_deleted;
 };
 
-/* Structure for "deny_rewrite" keyword. */
+/*
+ * tomoyo_no_rewrite_entry is a structure which is used for holding
+ * "deny_rewrite" entries.
+ * It has following fields.
+ *
+ *  (1) "list" which is linked to tomoyo_no_rewrite_list .
+ *  (2) "pattern" is a pathname which is by default not permitted to modify
+ *      already existing content.
+ *  (3) "is_deleted" is a bool which is true if marked as deleted, false
+ *      otherwise.
+ */
 struct tomoyo_no_rewrite_entry {
 	struct list_head list;
 	const struct tomoyo_path_info *pattern;
@@ -141,7 +170,31 @@ static int tomoyo_update_single_path_acl(const u8 type, const char *filename,
 					 struct tomoyo_domain_info *
 					 const domain, const bool is_delete);
 
-/* The list for "struct tomoyo_globally_readable_file_entry". */
+/*
+ * tomoyo_globally_readable_list is used for holding list of pathnames which
+ * are by default allowed to be open()ed for reading by any process.
+ *
+ * An entry is added by
+ *
+ * # echo 'allow_read /lib/libc-2.5.so' > \
+ *                               /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and is deleted by
+ *
+ * # echo 'delete allow_read /lib/libc-2.5.so' > \
+ *                               /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and all entries are retrieved by
+ *
+ * # grep ^allow_read /sys/kernel/security/tomoyo/exception_policy
+ *
+ * In the example above, any process is allowed to
+ * open("/lib/libc-2.5.so", O_RDONLY).
+ * One exception is, if the domain which current process belongs to is marked
+ * as "ignore_global_allow_read", current process can't do so unless explicitly
+ * given "allow_read /lib/libc-2.5.so" to the domain which current process
+ * belongs to.
+ */
 static LIST_HEAD(tomoyo_globally_readable_list);
 static DECLARE_RWSEM(tomoyo_globally_readable_list_lock);
 
@@ -256,7 +309,35 @@ bool tomoyo_read_globally_readable_policy(struct tomoyo_io_buffer *head)
 	return done;
 }
 
-/* The list for "struct tomoyo_pattern_entry". */
+/* tomoyo_pattern_list is used for holding list of pathnames which are used for
+ * converting pathnames to pathname patterns during learning mode.
+ *
+ * An entry is added by
+ *
+ * # echo 'file_pattern /proc/\$/mounts' > \
+ *                             /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and is deleted by
+ *
+ * # echo 'delete file_pattern /proc/\$/mounts' > \
+ *                             /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and all entries are retrieved by
+ *
+ * # grep ^file_pattern /sys/kernel/security/tomoyo/exception_policy
+ *
+ * In the example above, if a process which belongs to a domain which is in
+ * learning mode requested open("/proc/1/mounts", O_RDONLY),
+ * "allow_read /proc/\$/mounts" is automatically added to the domain which that
+ * process belongs to.
+ *
+ * It is not a desirable behavior that we have to use /proc/\$/ instead of
+ * /proc/self/ when current process needs to access only current process's
+ * information. As of now, LSM version of TOMOYO is using __d_path() for
+ * calculating pathname. Non LSM version of TOMOYO is using its own function
+ * which pretends as if /proc/self/ is not a symlink; so that we can forbid
+ * current process from accessing other process's information.
+ */
 static LIST_HEAD(tomoyo_pattern_list);
 static DECLARE_RWSEM(tomoyo_pattern_list_lock);
 
@@ -377,7 +458,35 @@ bool tomoyo_read_file_pattern(struct tomoyo_io_buffer *head)
 	return done;
 }
 
-/* The list for "struct tomoyo_no_rewrite_entry". */
+/*
+ * tomoyo_no_rewrite_list is used for holding list of pathnames which are by
+ * default forbidden to modify already written content of a file.
+ *
+ * An entry is added by
+ *
+ * # echo 'deny_rewrite /var/log/messages' > \
+ *                              /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and is deleted by
+ *
+ * # echo 'delete deny_rewrite /var/log/messages' > \
+ *                              /sys/kernel/security/tomoyo/exception_policy
+ *
+ * and all entries are retrieved by
+ *
+ * # grep ^deny_rewrite /sys/kernel/security/tomoyo/exception_policy
+ *
+ * In the example above, if a process requested to rewrite /var/log/messages ,
+ * the process can't rewrite unless the domain which that process belongs to
+ * has "allow_rewrite /var/log/messages" entry.
+ *
+ * It is not a desirable behavior that we have to add "\040(deleted)" suffix
+ * when we want to allow rewriting already unlink()ed file. As of now,
+ * LSM version of TOMOYO is using __d_path() for calculating pathname.
+ * Non LSM version of TOMOYO is using its own function which doesn't append
+ * " (deleted)" suffix if the file is already unlink()ed; so that we don't
+ * need to worry whether the file is already unlink()ed or not.
+ */
 static LIST_HEAD(tomoyo_no_rewrite_list);
 static DECLARE_RWSEM(tomoyo_no_rewrite_list_lock);
 
diff --git a/security/tomoyo/realpath.c b/security/tomoyo/realpath.c
index 3948f6b..5f2e332 100644
--- a/security/tomoyo/realpath.c
+++ b/security/tomoyo/realpath.c
@@ -265,7 +265,16 @@ static unsigned int tomoyo_quota_for_savename;
  */
 #define TOMOYO_MAX_HASH 256
 
-/* Structure for string data. */
+/*
+ * tomoyo_name_entry is a structure which is used for linking
+ * "struct tomoyo_path_info" into tomoyo_name_list .
+ *
+ * Since tomoyo_name_list manages a list of strings which are shared by
+ * multiple processes (whereas "struct tomoyo_path_info" inside
+ * "struct tomoyo_path_info_with_data" is not shared), a reference counter will
+ * be added to "struct tomoyo_name_entry" rather than "struct tomoyo_path_info"
+ * when TOMOYO starts supporting garbage collector.
+ */
 struct tomoyo_name_entry {
 	struct list_head list;
 	struct tomoyo_path_info entry;
@@ -279,10 +288,10 @@ struct tomoyo_free_memory_block_list {
 };
 
 /*
- * The list for "struct tomoyo_name_entry".
- *
- * This list is updated only inside tomoyo_save_name(), thus
- * no global mutex exists.
+ * tomoyo_name_list is used for holding string data used by TOMOYO.
+ * Since same string data is likely used for multiple times (e.g.
+ * "/lib/libc-2.5.so"), TOMOYO shares string data in the form of
+ * "const struct tomoyo_path_info *".
  */
 static struct list_head tomoyo_name_list[TOMOYO_MAX_HASH];
 
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index e42be5c..3194d09 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -262,6 +262,10 @@ static int tomoyo_dentry_open(struct file *f, const struct cred *cred)
 	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path, flags);
 }
 
+/*
+ * tomoyo_security_ops is a "struct security_operations" which is used for
+ * registering TOMOYO.
+ */
 static struct security_operations tomoyo_security_ops = {
 	.name                = "tomoyo",
 	.cred_prepare        = tomoyo_cred_prepare,