[TOMOYO #15 2/8] Memory and pathname management functions.

Kentaro Takeda
2009-02-05T08:55:32Z

TOMOYO Linux performs pathname based access control.
To remove factors that make pathname based access control difficult
(e.g. symbolic links, "..", "//" etc.), TOMOYO Linux derives realpath
of requested pathname from "struct dentry" and "struct vfsmount".

The maximum length of string data is limited to 4000 including trailing '\0'.
Since TOMOYO Linux uses '\ooo' style representation for non ASCII printable
characters, maybe TOMOYO Linux should be able to support 16336 (which means
(NAME_MAX * (PATH_MAX / (NAME_MAX + 1)) * 4 + (PATH_MAX / (NAME_MAX + 1)))
including trailing '\0'), but I think 4000 is enough for practical use.

TOMOYO uses only 0x21 - 0x7E (as printable characters) and 0x20 (as word
delimiter) and 0x0A (as line delimiter).
0x01 - 0x20 and 0x80 - 0xFF is handled in \ooo style representation.
The reason to use \ooo is to guarantee that "%s" won't damage logs.
Userland program can request

open("/tmp/file granted.\nAccess /tmp/file ", O_WRONLY | O_CREAT, 0600)

and logging such crazy pathname using "Access %s denied.\n" format will cause
"fabrication of logs" like

Access /tmp/file granted.
Access /tmp/file denied.

TOMOYO converts such characters to \ooo so that the logs will become

Access /tmp/file\040granted.\012Access\040/tmp/file denied.

and the administrator can read the logs safely using /bin/cat .
Likewise, a crazy request like

open("/tmp/\x01\x02\x03\x04\x05\x06\x07\x08\x09", O_WRONLY | O_CREAT, 0600)

will be processed safely by converting to

Access /tmp/\001\002\003\004\005\006\007\010\011 denied.

Signed-off-by: Kentaro Takeda <takedakn@nttdata.co.jp>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Toshiharu Harada <haradats@nttdata.co.jp>
---
security/tomoyo/realpath.c | 487 +++++++++++++++++++++++++++++++++++++++++++++
security/tomoyo/realpath.h | 63 +++++
2 files changed, 550 insertions(+)

--- /dev/null
+++ security-testing-2.6.git/security/tomoyo/realpath.c
@@ -0,0 +1,487 @@
+/*
+ * security/tomoyo/realpath.c
+ *
+ * Get the canonicalized absolute pathnames. The basis for TOMOYO.
+ *
+ * Copyright (C) 2005-2009 NTT DATA CORPORATION
+ *
+ * Version: 2.2.0-pre 2009/02/01
+ *
+ */
+
+#include <linux/types.h>
+#include <linux/mount.h>
+#include <linux/mnt_namespace.h>
+#include "common.h"
+#include "realpath.h"
+
+/**
+ * tomoyo_encode: Convert binary string to ascii string.
+ *
+ * @buffer: Buffer for ASCII string.
+ * @buflen: Size of @buffer.
+ * @str: Binary string.
+ *
+ * Returns 0 on success, -ENOMEM otherwise.
+ */
+int tomoyo_encode(char *buffer, int buflen, const char *str)
+{
+ while (1) {
+ const unsigned char c = *(unsigned char *) str++;
+
+ if (tomoyo_is_valid(c)) {
+ if (--buflen <= 0)
+ break;
+ *buffer++ = (char) c;
+ if (c != '\\')
+ continue;
+ if (--buflen <= 0)
+ break;
+ *buffer++ = (char) c;
+ continue;
+ }
+ if (!c) {
+ if (--buflen <= 0)
+ break;
+ *buffer = '\0';
+ return 0;
+ }
+ buflen -= 4;
+ if (buflen <= 0)
+ break;
+ *buffer++ = '\\';
+ *buffer++ = (c >> 6) + '0';
+ *buffer++ = ((c >> 3) & 7) + '0';
+ *buffer++ = (c & 7) + '0';
+ }
+ return -ENOMEM;
+}
+
+/**
+ * tomoyo_realpath_from_path2 - Returns realpath(3) of the given dentry but ignores chroot'ed root.
+ *
+ * @path: Pointer to "struct path".
+ * @newname: Pointer to buffer to return value in.
+ * @newname_len: Size of @newname.
+ *
+ * Returns 0 on success, negative value otherwise.
+ *
+ * If dentry is a directory, trailing '/' is appended.
+ * Characters out of 0x20 < c < 0x7F range are converted to
+ * \ooo style octal string.
+ * Character \ is converted to \\ string.
+ */
+int tomoyo_realpath_from_path2(struct path *path, char *newname,
+ int newname_len)
+{
+ int error = -ENOMEM;
+ struct dentry *dentry = path->dentry;
+ char *sp;
+
+ if (!dentry || !path->mnt || !newname || newname_len <= 2048)
+ return -EINVAL;
+ if (dentry->d_op && dentry->d_op->d_dname) {
+ /* For "socket:[\$]" and "pipe:[\$]". */
+ static const int offset = 1536;
+ sp = dentry->d_op->d_dname(dentry, newname + offset,
+ newname_len - offset);
+ } else {
+ /* Taken from d_namespace_path(). */
+ struct path root;
+ struct path ns_root = { };
+ struct path tmp;
+
+ read_lock(&current->fs->lock);
+ root = current->fs->root;
+ path_get(&root);
+ read_unlock(&current->fs->lock);
+ spin_lock(&vfsmount_lock);
+ if (root.mnt && root.mnt->mnt_ns)
+ ns_root.mnt = mntget(root.mnt->mnt_ns->root);
+ if (ns_root.mnt)
+ ns_root.dentry = dget(ns_root.mnt->mnt_root);
+ spin_unlock(&vfsmount_lock);
+ spin_lock(&dcache_lock);
+ tmp = ns_root;
+ sp = __d_path(path, &tmp, newname, newname_len);
+ spin_unlock(&dcache_lock);
+ path_put(&root);
+ path_put(&ns_root);
+ }
+ if (IS_ERR(sp))
+ error = PTR_ERR(sp);
+ else
+ error = tomoyo_encode(newname, sp - newname, sp);
+ /* Append trailing '/' if dentry is a directory. */
+ if (!error && dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)
+ && *newname) {
+ sp = newname + strlen(newname);
+ if (*(sp - 1) != '/') {
+ if (sp < newname + newname_len - 4) {
+ *sp++ = '/';
+ *sp = '\0';
+ } else {
+ error = -ENOMEM;
+ }
+ }
+ }
+ if (error)
+ printk(KERN_WARNING "tomoyo_realpath: Pathname too long.\n");
+ return error;
+}
+
+/**
+ * tomoyo_realpath_from_path - Returns realpath(3) of the given pathname but ignores chroot'ed root.
+ *
+ * @path: Pointer to "struct path".
+ *
+ * Returns the realpath of the given @path on success, NULL otherwise.
+ *
+ * These functions use tomoyo_alloc(), so the caller must call tomoyo_free()
+ * if these functions didn't return NULL.
+ */
+char *tomoyo_realpath_from_path(struct path *path)
+{
+ char *buf = tomoyo_alloc(sizeof(struct tomoyo_page_buffer));
+
+ BUILD_BUG_ON(sizeof(struct tomoyo_page_buffer)
+ <= TOMOYO_MAX_PATHNAME_LEN - 1);
+ if (!buf)
+ return NULL;
+ if (tomoyo_realpath_from_path2(path, buf,
+ TOMOYO_MAX_PATHNAME_LEN - 1) == 0)
+ return buf;
+ tomoyo_free(buf);
+ return NULL;
+}
+
+/**
+ * tomoyo_realpath - Get realpath of a pathname.
+ *
+ * @pathname: The pathname to solve.
+ *
+ * Returns the realpath of @pathname on success, NULL otherwise.
+ */
+char *tomoyo_realpath(const char *pathname)
+{
+ struct nameidata nd;
+
+ if (pathname && path_lookup(pathname, LOOKUP_FOLLOW, &nd) == 0) {
+ char *buf = tomoyo_realpath_from_path(&nd.path);
+ path_put(&nd.path);
+ return buf;
+ }
+ return NULL;
+}
+
+/**
+ * tomoyo_realpath_nofollow - Get realpath of a pathname.
+ *
+ * @pathname: The pathname to solve.
+ *
+ * Returns the realpath of @pathname on success, NULL otherwise.
+ */
+char *tomoyo_realpath_nofollow(const char *pathname)
+{
+ struct nameidata nd;
+
+ if (pathname && path_lookup(pathname, 0, &nd) == 0) {
+ char *buf = tomoyo_realpath_from_path(&nd.path);
+ path_put(&nd.path);
+ return buf;
+ }
+ return NULL;
+}
+
+/* Memory allocated for non-string data. */
+static unsigned int tomoyo_allocated_memory_for_elements;
+/* Quota for holding non-string data. */
+static unsigned int tomoyo_quota_for_elements;
+
+/**
+ * tomoyo_alloc_element - Allocate permanent memory for structures.
+ *
+ * @size: Size in bytes.
+ *
+ * Returns pointer to allocated memory on success, NULL otherwise.
+ *
+ * Memory has to be zeroed.
+ * The RAM is chunked, so NEVER try to kfree() the returned pointer.
+ */
+void *tomoyo_alloc_element(const unsigned int size)
+{
+ static char *buf;
+ static DEFINE_MUTEX(lock);
+ static unsigned int buf_used_len = PATH_MAX;
+ char *ptr = NULL;
+ /*Assumes sizeof(void *) >= sizeof(long) is true. */
+ const unsigned int word_aligned_size
+ = roundup(size, max(sizeof(void *), sizeof(long)));
+ if (word_aligned_size > PATH_MAX)
+ return NULL;
+ /***** EXCLUSIVE SECTION START *****/
+ mutex_lock(&lock);
+ if (buf_used_len + word_aligned_size > PATH_MAX) {
+ if (!tomoyo_quota_for_elements ||
+ tomoyo_allocated_memory_for_elements
+ + PATH_MAX <= tomoyo_quota_for_elements)
+ ptr = kzalloc(PATH_MAX, GFP_KERNEL);
+ if (!ptr) {
+ printk(KERN_WARNING "ERROR: Out of memory "
+ "for tomoyo_alloc_element().\n");
+ if (!tomoyo_policy_loaded)
+ panic("MAC Initialization failed.\n");
+ } else {
+ buf = ptr;
+ tomoyo_allocated_memory_for_elements += PATH_MAX;
+ buf_used_len = word_aligned_size;
+ ptr = buf;
+ }
+ } else if (word_aligned_size) {
+ int i;
+ ptr = buf + buf_used_len;
+ buf_used_len += word_aligned_size;
+ for (i = 0; i < word_aligned_size; i++) {
+ if (!ptr[i])
+ continue;
+ printk(KERN_ERR "WARNING: Reserved memory was tainted! "
+ "The system might go wrong.\n");
+ ptr[i] = '\0';
+ }
+ }
+ mutex_unlock(&lock);
+ /***** EXCLUSIVE SECTION END *****/
+ return ptr;
+}
+
+/* Memory allocated for string data in bytes. */
+static unsigned int tomoyo_allocated_memory_for_savename;
+/* Quota for holding string data in bytes. */
+static unsigned int tomoyo_quota_for_savename;
+
+/*
+ * TOMOYO uses this hash only when appending a string into the string
+ * table. Frequency of appending strings is very low. So we don't need
+ * large (e.g. 64k) hash size. 256 will be sufficient.
+ */
+#define TOMOYO_MAX_HASH 256
+
+/* Structure for string data. */
+struct tomoyo_name_entry {
+ struct list_head list;
+ struct tomoyo_path_info entry;
+};
+
+/* Structure for available memory region. */
+struct tomoyo_free_memory_block_list {
+ struct list_head list;
+ char *ptr; /* Pointer to a free area. */
+ int len; /* Length of the area. */
+};
+
+/*
+ * The list for "struct tomoyo_name_entry".
+ *
+ * This list is updated only inside tomoyo_save_name(), thus
+ * no global mutex exists.
+ */
+static struct list_head tomoyo_name_list[TOMOYO_MAX_HASH];
+
+/**
+ * tomoyo_save_name - Allocate permanent memory for string data.
+ *
+ * @name: The string to store into the permernent memory.
+ *
+ * Returns pointer to "struct tomoyo_path_info" on success, NULL otherwise.
+ *
+ * The RAM is shared, so NEVER try to modify or kfree() the returned name.
+ */
+const struct tomoyo_path_info *tomoyo_save_name(const char *name)
+{
+ static LIST_HEAD(fmb_list);
+ static DEFINE_MUTEX(lock);
+ struct tomoyo_name_entry *ptr;
+ unsigned int hash;
+ /* fmb contains available size in bytes.
+ fmb is removed from the fmb_list when fmb->len becomes 0. */
+ struct tomoyo_free_memory_block_list *fmb;
+ int len;
+ char *cp;
+
+ if (!name)
+ return NULL;
+ len = strlen(name) + 1;
+ if (len > TOMOYO_MAX_PATHNAME_LEN) {
+ printk(KERN_WARNING "ERROR: Name too long "
+ "for tomoyo_save_name().\n");
+ return NULL;
+ }
+ hash = full_name_hash((const unsigned char *) name, len - 1);
+ /***** EXCLUSIVE SECTION START *****/
+ mutex_lock(&lock);
+ list_for_each_entry(ptr, &tomoyo_name_list[hash % TOMOYO_MAX_HASH],
+ list) {
+ if (hash == ptr->entry.hash && !strcmp(name, ptr->entry.name))
+ goto out;
+ }
+ list_for_each_entry(fmb, &fmb_list, list) {
+ if (len <= fmb->len)
+ goto ready;
+ }
+ if (!tomoyo_quota_for_savename ||
+ tomoyo_allocated_memory_for_savename + PATH_MAX
+ <= tomoyo_quota_for_savename)
+ cp = kzalloc(PATH_MAX, GFP_KERNEL);
+ else
+ cp = NULL;
+ fmb = kzalloc(sizeof(*fmb), GFP_KERNEL);
+ if (!cp || !fmb) {
+ kfree(cp);
+ kfree(fmb);
+ printk(KERN_WARNING "ERROR: Out of memory "
+ "for tomoyo_save_name().\n");
+ if (!tomoyo_policy_loaded)
+ panic("MAC Initialization failed.\n");
+ ptr = NULL;
+ goto out;
+ }
+ tomoyo_allocated_memory_for_savename += PATH_MAX;
+ list_add(&fmb->list, &fmb_list);
+ fmb->ptr = cp;
+ fmb->len = PATH_MAX;
+ ready:
+ ptr = tomoyo_alloc_element(sizeof(*ptr));
+ if (!ptr)
+ goto out;
+ ptr->entry.name = fmb->ptr;
+ memmove(fmb->ptr, name, len);
+ tomoyo_fill_path_info(&ptr->entry);
+ fmb->ptr += len;
+ fmb->len -= len;
+ list_add_tail(&ptr->list, &tomoyo_name_list[hash % TOMOYO_MAX_HASH]);
+ if (fmb->len == 0) {
+ list_del(&fmb->list);
+ kfree(fmb);
+ }
+ out:
+ mutex_unlock(&lock);
+ /***** EXCLUSIVE SECTION END *****/
+ return ptr ? &ptr->entry : NULL;
+}
+
+/**
+ * tomoyo_realpath_init - Initialize realpath related code.
+ *
+ * Returns 0.
+ */
+static int __init tomoyo_realpath_init(void)
+{
+ int i;
+
+ BUILD_BUG_ON(TOMOYO_MAX_PATHNAME_LEN > PATH_MAX);
+ for (i = 0; i < TOMOYO_MAX_HASH; i++)
+ INIT_LIST_HEAD(&tomoyo_name_list[i]);
+ INIT_LIST_HEAD(&tomoyo_kernel_domain.acl_info_list);
+ tomoyo_kernel_domain.domainname = tomoyo_save_name(TOMOYO_ROOT_NAME);
+ list_add_tail(&tomoyo_kernel_domain.list, &tomoyo_domain_list);
+ down_read(&tomoyo_domain_list_lock);
+ if (tomoyo_find_domain(TOMOYO_ROOT_NAME) != &tomoyo_kernel_domain)
+ panic("Can't register tomoyo_kernel_domain");
+ up_read(&tomoyo_domain_list_lock);
+ return 0;
+}
+
+security_initcall(tomoyo_realpath_init);
+
+/* Memory allocated for temporary purpose. */
+static atomic_t tomoyo_dynamic_memory_size;
+
+/**
+ * tomoyo_alloc - Allocate memory for temporary purpose.
+ *
+ * @size: Size in bytes.
+ *
+ * Returns pointer to allocated memory on success, NULL otherwise.
+ */
+void *tomoyo_alloc(const size_t size)
+{
+ void *p = kzalloc(size, GFP_KERNEL);
+ if (p)
+ atomic_add(ksize(p), &tomoyo_dynamic_memory_size);
+ return p;
+}
+
+/**
+ * tomoyo_free - Release memory allocated by tomoyo_alloc().
+ *
+ * @p: Pointer returned by tomoyo_alloc(). May be NULL.
+ *
+ * Returns nothing.
+ */
+void tomoyo_free(const void *p)
+{
+ if (p) {
+ atomic_sub(ksize(p), &tomoyo_dynamic_memory_size);
+ kfree(p);
+ }
+}
+
+/**
+ * tomoyo_read_memory_counter - Check for memory usage in bytes.
+ *
+ * @head: Pointer to "struct tomoyo_io_buffer".
+ *
+ * Returns memory usage.
+ */
+int tomoyo_read_memory_counter(struct tomoyo_io_buffer *head)
+{
+ if (!head->read_eof) {
+ const unsigned int shared
+ = tomoyo_allocated_memory_for_savename;
+ const unsigned int private
+ = tomoyo_allocated_memory_for_elements;
+ const unsigned int dynamic
+ = atomic_read(&tomoyo_dynamic_memory_size);
+ char buffer[64];
+
+ memset(buffer, 0, sizeof(buffer));
+ if (tomoyo_quota_for_savename)
+ snprintf(buffer, sizeof(buffer) - 1,
+ " (Quota: %10u)",
+ tomoyo_quota_for_savename);
+ else
+ buffer[0] = '\0';
+ tomoyo_io_printf(head, "Shared: %10u%s\n", shared, buffer);
+ if (tomoyo_quota_for_elements)
+ snprintf(buffer, sizeof(buffer) - 1,
+ " (Quota: %10u)",
+ tomoyo_quota_for_elements);
+ else
+ buffer[0] = '\0';
+ tomoyo_io_printf(head, "Private: %10u%s\n", private, buffer);
+ tomoyo_io_printf(head, "Dynamic: %10u\n", dynamic);
+ tomoyo_io_printf(head, "Total: %10u\n",
+ shared + private + dynamic);
+ head->read_eof = true;
+ }
+ return 0;
+}
+
+/**
+ * tomoyo_write_memory_quota - Set memory quota.
+ *
+ * @head: Pointer to "struct tomoyo_io_buffer".
+ *
+ * Returns 0.
+ */
+int tomoyo_write_memory_quota(struct tomoyo_io_buffer *head)
+{
+ char *data = head->write_buf;
+ unsigned int size;
+
+ if (sscanf(data, "Shared: %u", &size) == 1)
+ tomoyo_quota_for_savename = size;
+ else if (sscanf(data, "Private: %u", &size) == 1)
+ tomoyo_quota_for_elements = size;
+ return 0;
+}
--- /dev/null
+++ security-testing-2.6.git/security/tomoyo/realpath.h
@@ -0,0 +1,63 @@
+/*
+ * security/tomoyo/realpath.h
+ *
+ * Get the canonicalized absolute pathnames. The basis for TOMOYO.
+ *
+ * Copyright (C) 2005-2009 NTT DATA CORPORATION
+ *
+ * Version: 2.2.0-pre 2009/02/01
+ *
+ */
+
+#ifndef _SECURITY_TOMOYO_REALPATH_H
+#define _SECURITY_TOMOYO_REALPATH_H
+
+struct path;
+struct tomoyo_path_info;
+struct tomoyo_io_buffer;
+
+/* Convert binary string to ascii string. */
+int tomoyo_encode(char *buffer, int buflen, const char *str);
+
+/* Returns realpath(3) of the given pathname but ignores chroot'ed root. */
+int tomoyo_realpath_from_path2(struct path *path, char *newname,
+ int newname_len);
+
+/*
+ * Returns realpath(3) of the given pathname but ignores chroot'ed root.
+ * These functions use tomoyo_alloc(), so the caller must call tomoyo_free()
+ * if these functions didn't return NULL.
+ */
+char *tomoyo_realpath(const char *pathname);
+/*
+ * Same with tomoyo_realpath() except that it doesn't follow the final symlink.
+ */
+char *tomoyo_realpath_nofollow(const char *pathname);
+/* Same with tomoyo_realpath() except that the pathname is already solved. */
+char *tomoyo_realpath_from_path(struct path *path);
+
+/*
+ * Allocate memory for ACL entry.
+ * The RAM is chunked, so NEVER try to kfree() the returned pointer.
+ */
+void *tomoyo_alloc_element(const unsigned int size);
+
+/*
+ * Keep the given name on the RAM.
+ * The RAM is shared, so NEVER try to modify or kfree() the returned name.
+ */
+const struct tomoyo_path_info *tomoyo_save_name(const char *name);
+
+/* Allocate memory for temporary use (e.g. permission checks). */
+void *tomoyo_alloc(const size_t size);
+
+/* Free memory allocated by tomoyo_alloc(). */
+void tomoyo_free(const void *p);
+
+/* Check for memory usage. */
+int tomoyo_read_memory_counter(struct tomoyo_io_buffer *head);
+
+/* Set memory quota. */
+int tomoyo_write_memory_quota(struct tomoyo_io_buffer *head);
+
+#endif /* !defined(_SECURITY_TOMOYO_REALPATH_H) */

--