[TOMOYO #4 03/13] Memory and pathname management functions.

[Tetsuo Handa]

Basic functions to get canonicalized absolute pathnames
for TOMOYO Linux. Even the requested pathname is symlink()ed
or chroot()ed, TOMOYO Linux uses the original pathname.

Signed-off-by: Kentaro Takeda <takedakn@xxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 security/tomoyo/realpath.c |  713 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 713 insertions(+)

--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/security/tomoyo/realpath.c	2007-10-11 15:53:12.000000000 +0900
@@ -0,0 +1,713 @@
+/*
+ * security/tomoyo/realpath.c
+ *
+ * Get the canonicalized absolute pathnames.
+ * The basis for TOMOYO Linux.
+ */
+
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/utime.h>
+#include <linux/file.h>
+#include <linux/smp_lock.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <asm/atomic.h>
+#include <linux/namei.h>
+#include <linux/mount.h>
+#include <linux/proc_fs.h>
+#include <linux/sysctl.h>
+#include "realpath.h"
+#include "tomoyo.h"
+
+/***** realpath handler *****/
+
+static int tmy_print_ascii(const char *sp, const char *cp,
+			   int *buflen0, char **end0)
+{
+	int buflen = *buflen0;
+	char *end = *end0;
+
+	while (sp <= cp) {
+		unsigned char c;
+
+		c = *(unsigned char *) cp;
+		if (c == '\\') {
+			buflen -= 2;
+			if (buflen < 0)
+				goto out;
+			*--end = '\\';
+			*--end = '\\';
+		} else if (c > ' ' && c < 127) {
+			if (--buflen < 0)
+				goto out;
+			*--end = (char) c;
+		} else {
+			buflen -= 4;
+			if (buflen < 0)
+				goto out;
+			*--end = (c & 7) + '0';
+			*--end = ((c >> 3) & 7) + '0';
+			*--end = (c >> 6) + '0';
+			*--end = '\\';
+		}
+		cp--;
+	}
+
+	*buflen0 = buflen;
+	*end0 = end;
+
+	return 0;
+out: ;
+	return -ENOMEM;
+}
+
+/**
+ * tmy_get_absolute_path - return the realpath of a dentry.
+ * @dentry: pointer to "struct dentry".
+ * @vfsmnt: pointer to "struct vfsmount" to which the @dentry belongs.
+ * @buffer: size of buffer to save the result.
+ * @buflen: size of @buffer .
+ *
+ * Returns zero on success.
+ * Returns nonzero on failure.
+ *
+ * Caller holds the dcache_lock.
+ * Based on __d_path() in fs/dcache.c
+ *
+ * Unlike d_path(), this function traverses upto the root directory of
+ * process's namespace.
+ *
+ * If @dentry is a directory, trailing '/' is appended.
+ * Characters other than ' ' < c < 127 are converted to \ooo style octal string.
+ * Character \ is converted to \\ string.
+ */
+static int tmy_get_absolute_path(struct dentry *dentry,
+				 struct vfsmount *vfsmnt,
+				 char *buffer,
+				 int buflen)
+{
+	char *start = buffer;
+	char *end = buffer + buflen;
+	u8 is_dir = (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode));
+	const char *sp;
+	const char *cp;
+
+	if (buflen < 256)
+		goto out;
+
+	*--end = '\0';
+	buflen--;
+
+	while (1) {
+		struct dentry *parent;
+
+		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
+			/* Global root? */
+			spin_lock(&vfsmount_lock);
+			if (vfsmnt->mnt_parent == vfsmnt) {
+				spin_unlock(&vfsmount_lock);
+				break;
+			}
+			dentry = vfsmnt->mnt_mountpoint;
+			vfsmnt = vfsmnt->mnt_parent;
+			spin_unlock(&vfsmount_lock);
+			continue;
+		}
+
+		if (is_dir) {
+			is_dir = 0;
+			*--end = '/';
+			buflen--;
+		}
+
+		parent = dentry->d_parent;
+		sp = dentry->d_name.name;
+		cp = sp + dentry->d_name.len - 1;
+
+		/* Exception: Use /proc/self/ rather than */
+		/* /proc/\$/ for current process. */
+		if (IS_ROOT(parent) &&
+		    *sp > '0' && *sp <= '9' && parent->d_sb &&
+		    parent->d_sb->s_magic == PROC_SUPER_MAGIC) {
+
+			char *ep;
+			const pid_t pid = (pid_t) simple_strtoul(sp, &ep, 10);
+
+			if (!*ep && pid == current->tgid) {
+				sp = "self";
+				cp = sp + 3;
+			}
+
+		}
+
+		if (tmy_print_ascii(sp, cp, &buflen, &end))
+			goto out;
+
+		if (--buflen < 0)
+			goto out;
+		*--end = '/';
+
+		dentry = parent;
+	}
+	if (*end == '/') {
+		buflen++;
+		end++;
+	}
+
+	sp = dentry->d_name.name;
+	cp = sp + dentry->d_name.len - 1;
+
+	if (tmy_print_ascii(sp, cp, &buflen, &end))
+		goto out;
+
+	/* Move the pathname to the top of the buffer. */
+	memmove(start, end, strlen(end) + 1);
+	return 0;
+out: ;
+	return -ENOMEM;
+}
+
+/**
+ * tmy_realpath_dentry2 - return the realpath of a dentry.
+ * @dentry:      pointer to "struct dentry".
+ * @mnt:         pointer to "struct vfsmount" to which the @dentry belongs.
+ * @newname:     buffer to save the result.
+ * @newname_len: size of @newname .
+ *
+ * Returns zero on success.
+ * Returns nonzero on failure.
+ */
+int tmy_realpath_dentry2(struct dentry *dentry,
+			 struct vfsmount *mnt,
+			 char *newname,
+			 int newname_len)
+{
+	int error;
+	struct dentry *d_dentry;
+	struct vfsmount *d_mnt;
+
+	if (!dentry || !mnt || !newname || newname_len <= 0)
+		return -EINVAL;
+
+	d_dentry = dget(dentry);
+	d_mnt = mntget(mnt);
+
+	/***** CRITICAL SECTION START *****/
+	spin_lock(&dcache_lock);
+	error = tmy_get_absolute_path(d_dentry, d_mnt, newname, newname_len);
+	spin_unlock(&dcache_lock);
+	/***** CRITICAL SECTION END *****/
+
+	dput(d_dentry);
+	mntput(d_mnt);
+	return error;
+}
+
+/**
+ * tmy_realpath_dentry - return the realpath of a dentry.
+ * @dentry: pointer to "struct dentry".
+ * @mnt:    pointer to "struct vfsmount" to which the @dentry belongs.
+ *
+ * Returns realpath(3) of the @dentry on success.
+ * Returns NULL on failure.
+ *
+ * This function uses tmy_alloc(), so caller must call tmy_free()
+ * if this function didn't return NULL.
+ */
+char *tmy_realpath_dentry(struct dentry *dentry, struct vfsmount *mnt)
+{
+	char *buf = tmy_alloc(TMY_MAX_PATHNAME_LEN);
+
+	if (buf &&
+	    tmy_realpath_dentry2(dentry, mnt, buf,
+				 TMY_MAX_PATHNAME_LEN - 1) == 0)
+		return buf;
+
+	tmy_free(buf);
+	return NULL;
+}
+
+/**
+ * tmy_realpath - return the realpath of a pathname.
+ * @pathname: pathname to report.
+ *
+ * Returns realpath(3) of the @pathname on success.
+ * Returns NULL on failure.
+ *
+ * This function uses tmy_alloc(), so caller must call tmy_free()
+ * if this function didn't return NULL.
+ */
+char *tmy_realpath(const char *pathname)
+{
+	struct nameidata nd;
+
+	if (pathname && path_lookup(pathname, LOOKUP_FOLLOW, &nd) == 0) {
+		char *buf = tmy_realpath_dentry(nd.dentry, nd.mnt);
+
+		path_release(&nd);
+		return buf;
+	}
+
+	return NULL;
+}
+
+/**
+ * tmy_realpath_nofollow - return the realpath of a pathname.
+ * @pathname: pathname to report.
+ *
+ * Returns realpath(3) of the @pathname on success.
+ * Returns NULL on failure.
+ *
+ * Unlike tmy_realpath(), this function doesn't follow if @pathname is
+ * a symbolic link.
+ *
+ * This function uses tmy_alloc(), so caller must call tmy_free()
+ * if this function didn't return NULL.
+ */
+char *tmy_realpath_nofollow(const char *pathname)
+{
+	struct nameidata nd;
+
+	if (pathname && path_lookup(pathname, 0, &nd) == 0) {
+		char *buf = tmy_realpath_dentry(nd.dentry, nd.mnt);
+
+		path_release(&nd);
+		return buf;
+	}
+
+	return NULL;
+}
+
+/* tmy_get_absolute_path() for "struct ctl_table". */
+static int tmy_sysctl_path(struct ctl_table *table, char *buffer, int buflen)
+{
+	char *end = buffer + buflen;
+
+	if (buflen < 256)
+		goto out;
+
+	*--end = '\0';
+	buflen--;
+
+	buflen -= 9; /* for "/proc/sys" prefix */
+
+	while (table) {
+		char buf[32];
+		const char *sp = table->procname;
+		const char *cp;
+
+		if (!sp) {
+			memset(buf, 0, sizeof(buf));
+			snprintf(buf, sizeof(buf) - 1, "=%d=", table->ctl_name);
+			sp = buf;
+		}
+		cp = strchr(sp, '\0') - 1;
+
+		if (tmy_print_ascii(sp, cp, &buflen, &end))
+			goto out;
+
+		if (--buflen < 0)
+			goto out;
+
+		*--end = '/';
+		table = table->parent;
+	}
+
+	/* Move the pathname to the top of the buffer. */
+	memmove(buffer, "/proc/sys", 9);
+	memmove(buffer + 9, end, strlen(end) + 1);
+	return 0;
+out: ;
+	return -ENOMEM;
+}
+
+/**
+ * sysctlpath_from_table - return the realpath of a ctl_table.
+ * @table: pointer to "struct ctl_table".
+ *
+ * Returns realpath(3) of the @table on success.
+ * Returns NULL on failure.
+ *
+ * This function uses tmy_alloc(), so caller must call tmy_free()
+ * if this function didn't return NULL.
+ */
+char *sysctlpath_from_table(struct ctl_table *table)
+{
+	char *buf = tmy_alloc(TMY_MAX_PATHNAME_LEN);
+
+	if (buf && tmy_sysctl_path(table, buf, TMY_MAX_PATHNAME_LEN - 1) == 0)
+		return buf;
+
+	tmy_free(buf);
+	return NULL;
+}
+
+/***** Private memory allocator. *****/
+
+/*
+ * Round up an integer so that the returned pointers are appropriately aligned.
+ * FIXME: Are there more requirements that is needed for assigning value
+ * atomically?
+ */
+static inline unsigned int tmy_roundup(const unsigned int size)
+{
+	if (sizeof(void *) >= sizeof(long))
+		return ((size + sizeof(void *) - 1) / sizeof(void *))
+			* sizeof(void *);
+
+	return ((size + sizeof(long) - 1) / sizeof(long)) * sizeof(long);
+}
+
+static unsigned int allocated_memory_for_elements;
+
+/**
+ * tmy_get_memory_used_for_elements - get memory usage for private data.
+ *
+ * Returns size of memory allocated for keeping individual ACL elements.
+ */
+unsigned int tmy_get_memory_used_for_elements(void)
+{
+	return allocated_memory_for_elements;
+}
+
+/**
+ * tmy_alloc_element - allocate memory for structures.
+ * @size: requested size in bytes.
+ *
+ * Returns '\0'-initialized memory region on success.
+ * Returns NULL on failure.
+ *
+ * This function allocates memory for keeping ACL entries.
+ * The RAM is chunked, so NEVER try to kfree() the returned pointer.
+ */
+void *tmy_alloc_element(const unsigned int size)
+{
+	static DEFINE_MUTEX(lock);
+	static char *buf;
+	static unsigned int buf_used_len = PAGE_SIZE;
+	char *ptr = NULL;
+	const unsigned int word_aligned_size = tmy_roundup(size);
+
+	if (word_aligned_size > PAGE_SIZE)
+		return NULL;
+
+	mutex_lock(&lock);
+
+	if (buf_used_len + word_aligned_size > PAGE_SIZE) {
+		ptr = kzalloc(PAGE_SIZE, GFP_KERNEL);
+
+		if (!ptr) {
+			printk(KERN_INFO "ERROR: "
+			       "Out of memory for tmy_alloc_element().\n");
+			if (!sbin_init_started)
+				panic("MAC Initialization failed.\n");
+		} else {
+			buf = ptr;
+			allocated_memory_for_elements += PAGE_SIZE;
+			buf_used_len = word_aligned_size;
+			ptr = buf;
+		}
+
+	} else if (word_aligned_size) {
+		unsigned int i;
+
+		ptr = buf + buf_used_len;
+		buf_used_len += word_aligned_size;
+
+		for (i = 0; i < word_aligned_size; i++) {
+			if (ptr[i]) { /* This must not happen! */
+				printk(KERN_ERR
+				       "WARNING: Reserved memory was tainted! "
+				       "The system might go wrong.\n");
+				ptr[i] = '\0';
+			}
+		}
+
+	}
+
+	mutex_unlock(&lock);
+	return ptr;
+}
+
+/***** Shared memory allocator. *****/
+
+static unsigned int allocated_memory_for_savename;
+
+/**
+ * tmy_get_memory_used_for_save_name - get memory usage for shared data.
+ *
+ * Returns size of memory allocated for keeping string tokens.
+ */
+unsigned int tmy_get_memory_used_for_save_name(void)
+{
+	return allocated_memory_for_savename;
+}
+
+#define MAX_HASH 256
+
+/* List of tokens. */
+struct name_entry {
+	struct list_head list;
+	struct path_info entry;
+};
+
+/* List of free memory. */
+struct free_memory_block_list {
+	struct list_head list;
+	char *ptr; /* Pointer to a free area. */
+	int len;   /* Length of the area.     */
+};
+
+/**
+ * tmy_save_name - keep the given token on the RAM.
+ * @name: the string token to remember.
+ *
+ * Returns pointer to memory region on success.
+ * Returns NULL on failure.
+ *
+ * This function allocates memory for keeping any string data.
+ * The RAM is shared, so NEVER try to modify or kfree() the returned name.
+ */
+const struct path_info *tmy_save_name(const char *name)
+{
+	static LIST_HEAD(fmb_list);
+	struct free_memory_block_list *fmb;
+	static struct name_entry name_list[MAX_HASH]; /* The list of names. */
+	struct name_entry *ptr;
+	static DEFINE_MUTEX(mutex);
+	unsigned int hash;
+	int len;
+	static int first_call = 1;
+	u8 found = 0;
+
+	if (!name)
+		return NULL;
+
+	len = strlen(name) + 1;
+	if (len > TMY_MAX_PATHNAME_LEN) {
+		printk(KERN_INFO "ERROR: Name too long for tmy_save_name().\n");
+		return NULL;
+	}
+
+	hash = full_name_hash((const unsigned char *) name, len - 1);
+
+	mutex_lock(&mutex);
+
+	if (first_call) {
+		int i;
+
+		first_call = 0;
+		memset(&name_list, 0, sizeof(name_list));
+
+		for (i = 0; i < MAX_HASH; i++) {
+			INIT_LIST_HEAD(&name_list[i].list);
+			name_list[i].entry.name = "/";
+			tmy_fill_path_info(&name_list[i].entry);
+		}
+
+		if (TMY_MAX_PATHNAME_LEN > PAGE_SIZE)
+			panic("Bad size.");
+	}
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(ptr, &name_list[hash % MAX_HASH].list, list) {
+		if (hash != ptr->entry.hash ||
+		    strcmp(name, ptr->entry.name))
+			continue;
+		found = 1;
+		break;
+	}
+	rcu_read_unlock();
+	if (found)
+		goto out;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(fmb, &fmb_list, list) {
+		if (len <= fmb->len) {
+			found = 1;
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	if (!found) {
+		char *cp;
+		cp = kzalloc(PAGE_SIZE, GFP_KERNEL);
+		if (!cp)
+			goto out2;
+
+		fmb = tmy_alloc_element(sizeof(*fmb));
+		if (!fmb) {
+			kfree(cp);
+out2: ;
+			printk(KERN_INFO
+			       "ERROR: Out of memory for tmy_save_name().\n");
+			if (!sbin_init_started)
+				panic("MAC Initialization failed.\n");
+			goto out; /* ptr == NULL */
+		}
+		allocated_memory_for_savename += PAGE_SIZE;
+		fmb->ptr = cp;
+		fmb->len = PAGE_SIZE;
+		mb(); /* Avoid out-of-order execution. */
+		/* RCU: Protected by mutex. */
+		list_add_tail_rcu(&fmb->list, &fmb_list);
+	}
+
+	ptr = tmy_alloc_element(sizeof(*ptr));
+	if (!ptr)
+		goto out;
+
+	ptr->entry.name = fmb->ptr;
+	memmove(fmb->ptr, name, len);
+	tmy_fill_path_info(&ptr->entry);
+	fmb->ptr += len;
+	fmb->len -= len;
+	mb(); /* Avoid out-of-order execution. */
+	/* RCU: Protected by mutex. */
+	list_add_tail_rcu(&ptr->list, &name_list[hash % MAX_HASH].list);
+	if (fmb->len == 0)
+		list_del_rcu(&fmb->list);
+out: ;
+	mutex_unlock(&mutex);
+	return ptr ? &ptr->entry : NULL;
+}
+
+/***** Dynamic memory allocator. *****/
+
+/* List of temporary memory blocks. */
+struct cache_entry {
+	struct rcu_head rcu;
+	struct list_head list;
+	void *ptr;
+	int size;
+};
+
+static DEFINE_SPINLOCK(cache_list_lock);
+static struct kmem_cache *tmy_cachep;
+
+/**
+ * tmy_realpath_init - initialize memory allocator.
+ */
+static int __init tmy_realpath_init(void)
+{
+	tmy_cachep = kmem_cache_create("tomoyo_cache",
+				       sizeof(struct cache_entry),
+				       0, SLAB_PANIC, NULL);
+	return 0;
+}
+postcore_initcall(tmy_realpath_init);
+
+
+static LIST_HEAD(cache_list);
+static unsigned int dynamic_memory_size;
+
+/**
+ * tmy_get_memory_used_for_dynamic - get memory usage for temporary purpose.
+ *
+ * Returns size of memory allocated for keeping temporary purpose.
+ */
+unsigned int tmy_get_memory_used_for_dynamic(void)
+{
+	return dynamic_memory_size;
+}
+
+/**
+ * tmy_alloc - allocate memory for temporary purpose.
+ * @size: requested size in bytes.
+ *
+ * Returns '\0'-initialized memory region on success.
+ * Returns NULL on failure.
+ *
+ * This function allocates memory for keeping ACL entries.
+ * The caller has to call tmy_free() the returned pointer
+ * when memory is no longer needed.
+ */
+void *tmy_alloc(const size_t size)
+{
+	void *ret = kzalloc(size, GFP_KERNEL);
+	struct cache_entry *new_entry;
+
+	if (!ret) {
+		printk(KERN_INFO "ERROR: "
+		       "kmalloc(): Out of memory for tmy_alloc().\n");
+		return ret;
+	}
+
+	new_entry = kmem_cache_alloc(tmy_cachep, GFP_KERNEL);
+
+	if (!new_entry) {
+		printk(KERN_INFO "ERROR: "
+		       "kmem_cache_alloc(): Out of memory for tmy_alloc().\n");
+		kfree(ret);
+		ret = NULL;
+	} else {
+
+		/* INIT_RCU_HEAD(&new_entry->rcu); */
+		INIT_LIST_HEAD(&new_entry->list);
+		new_entry->ptr = ret;
+		new_entry->size = ksize(ret);
+
+		/***** CRITICAL SECTION START *****/
+		spin_lock(&cache_list_lock);
+		list_add_rcu(&new_entry->list, &cache_list);
+		dynamic_memory_size += new_entry->size;
+		spin_unlock(&cache_list_lock);
+		/***** CRITICAL SECTION END *****/
+	}
+
+	return ret;
+}
+
+/* callback function for call_rcu(). */
+static void tmy_free_cachep(struct rcu_head *head)
+{
+	struct cache_entry *entry;
+	entry = container_of(head, struct cache_entry, rcu);
+	kmem_cache_free(tmy_cachep, entry);
+}
+
+/**
+ * tmy_free - free memory allocated by tmy_alloc().
+ * @p: pointer to memory block allocated by tmy_alloc().
+ *
+ * If caller calls this function for multiple times (i.e. double-free() bug) or
+ * calls this function with invalid pointer, warning message will appear.
+ * If caller forgets to call this function,
+ * tmy_get_memory_used_for_dynamic() will indicate memory leaks.
+ */
+void tmy_free(const void *p)
+{
+	struct list_head *pos;
+	struct list_head *tmp;
+	struct cache_entry *entry = NULL;
+	u8 found = 0;
+	if (!p)
+		return;
+
+	rcu_read_lock();
+	list_for_each_safe_rcu(pos, tmp, &cache_list) {
+		entry = list_entry(pos, struct cache_entry, list);
+		if (entry->ptr != p)
+			continue;
+		/***** CRITICAL SECTION START *****/
+		spin_lock(&cache_list_lock);
+		if (entry->ptr) {
+			list_del_rcu(&entry->list);
+			dynamic_memory_size -= entry->size;
+			found = 1;
+		}
+		entry->ptr = NULL;
+		spin_unlock(&cache_list_lock);
+		/***** CRITICAL SECTION END *****/
+		break;
+	}
+	rcu_read_unlock();
+	if (found) {
+		call_rcu(&entry->rcu, tmy_free_cachep);
+		kfree(p);
+	} else
+		printk(KERN_INFO "BUG: tmy_free() with invalid pointer.\n");
+}

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