AppArmor: misc. base functions and defines

Miscellaneous functions and defines needed by AppArmor, including
the base path resolution routines.

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

1 files changed, 235 insertions, 0 deletions

diff --git a/security/apparmor/path.c b/security/apparmor/path.c
new file mode 100644
index 000000000000..96bab9469d48
--- /dev/null
+++ b/security/apparmor/path.c
@@ -0,0 +1,235 @@
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor function for pathnames
+ *
+ * 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.
+ */
+
+#include <linux/magic.h>
+#include <linux/mnt_namespace.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/nsproxy.h>
+#include <linux/path.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/fs_struct.h>
+
+#include "include/apparmor.h"
+#include "include/path.h"
+#include "include/policy.h"
+
+
+/* modified from dcache.c */
+static int prepend(char **buffer, int buflen, const char *str, int namelen)
+{
+        buflen -= namelen;
+        if (buflen < 0)
+                return -ENAMETOOLONG;
+        *buffer -= namelen;
+        memcpy(*buffer, str, namelen);
+        return 0;
+}
+
+#define CHROOT_NSCONNECT (PATH_CHROOT_REL | PATH_CHROOT_NSCONNECT)
+
+/**
+ * d_namespace_path - lookup a name associated with a given path
+ * @path: path to lookup  (NOT NULL)
+ * @buf:  buffer to store path to  (NOT NULL)
+ * @buflen: length of @buf
+ * @name: Returns - pointer for start of path name with in @buf (NOT NULL)
+ * @flags: flags controlling path lookup
+ *
+ * Handle path name lookup.
+ *
+ * Returns: %0 else error code if path lookup fails
+ *          When no error the path name is returned in @name which points to
+ *          to a position in @buf
+ */
+static int d_namespace_path(struct path *path, char *buf, int buflen,
+                            char **name, int flags)
+{
+        struct path root, tmp;
+        char *res;
+        int deleted, connected;
+        int error = 0;
+
+        /* Get the root we want to resolve too */
+        if (flags & PATH_CHROOT_REL) {
+                /* resolve paths relative to chroot */
+                read_lock(&current->fs->lock);
+                root = current->fs->root;
+                /* released below */
+                path_get(&root);
+                read_unlock(&current->fs->lock);
+        } else {
+                /* resolve paths relative to namespace */
+                root.mnt = current->nsproxy->mnt_ns->root;
+                root.dentry = root.mnt->mnt_root;
+                /* released below */
+                path_get(&root);
+        }
+
+        spin_lock(&dcache_lock);
+        /* There is a race window between path lookup here and the
+         * need to strip the " (deleted) string that __d_path applies
+         * Detect the race and relookup the path
+         *
+         * The stripping of (deleted) is a hack that could be removed
+         * with an updated __d_path
+         */
+        do {
+                tmp = root;
+                deleted = d_unlinked(path->dentry);
+                res = __d_path(path, &tmp, buf, buflen);
+
+        } while (deleted != d_unlinked(path->dentry));
+        spin_unlock(&dcache_lock);
+
+        *name = res;
+        /* handle error conditions - and still allow a partial path to
+         * be returned.
+         */
+        if (IS_ERR(res)) {
+                error = PTR_ERR(res);
+                *name = buf;
+                goto out;
+        }
+        if (deleted) {
+                /* On some filesystems, newly allocated dentries appear to the
+                 * security_path hooks as a deleted dentry except without an
+                 * inode allocated.
+                 *
+                 * Remove the appended deleted text and return as string for
+                 * normal mediation, or auditing.  The (deleted) string is
+                 * guaranteed to be added in this case, so just strip it.
+                 */
+                buf[buflen - 11] = 0;   /* - (len(" (deleted)") +\0) */
+
+                if (path->dentry->d_inode && !(flags & PATH_MEDIATE_DELETED)) {
+                        error = -ENOENT;
+                        goto out;
+                }
+        }
+
+        /* Determine if the path is connected to the expected root */
+        connected = tmp.dentry == root.dentry && tmp.mnt == root.mnt;
+
+        /* If the path is not connected,
+         * check if it is a sysctl and handle specially else remove any
+         * leading / that __d_path may have returned.
+         * Unless
+         *     specifically directed to connect the path,
+         * OR
+         *     if in a chroot and doing chroot relative paths and the path
+         *     resolves to the namespace root (would be connected outside
+         *     of chroot) and specifically directed to connect paths to
+         *     namespace root.
+         */
+        if (!connected) {
+                /* is the disconnect path a sysctl? */
+                if (tmp.dentry->d_sb->s_magic == PROC_SUPER_MAGIC &&
+                    strncmp(*name, "/sys/", 5) == 0) {
+                        /* TODO: convert over to using a per namespace
+                         * control instead of hard coded /proc
+                         */
+                        error = prepend(name, *name - buf, "/proc", 5);
+                } else if (!(flags & PATH_CONNECT_PATH) &&
+                           !(((flags & CHROOT_NSCONNECT) == CHROOT_NSCONNECT) &&
+                             (tmp.mnt == current->nsproxy->mnt_ns->root &&
+                              tmp.dentry == tmp.mnt->mnt_root))) {
+                        /* disconnected path, don't return pathname starting
+                         * with '/'
+                         */
+                        error = -ESTALE;
+                        if (*res == '/')
+                                *name = res + 1;
+                }
+        }
+
+out:
+        path_put(&root);
+
+        return error;
+}
+
+/**
+ * get_name_to_buffer - get the pathname to a buffer ensure dir / is appended
+ * @path: path to get name for  (NOT NULL)
+ * @flags: flags controlling path lookup
+ * @buffer: buffer to put name in  (NOT NULL)
+ * @size: size of buffer
+ * @name: Returns - contains position of path name in @buffer (NOT NULL)
+ *
+ * Returns: %0 else error on failure
+ */
+static int get_name_to_buffer(struct path *path, int flags, char *buffer,
+                              int size, char **name)
+{
+        int adjust = (flags & PATH_IS_DIR) ? 1 : 0;
+        int error = d_namespace_path(path, buffer, size - adjust, name, flags);
+
+        if (!error && (flags & PATH_IS_DIR) && (*name)[1] != '\0')
+                /*
+                 * Append "/" to the pathname.  The root directory is a special
+                 * case; it already ends in slash.
+                 */
+                strcpy(&buffer[size - 2], "/");
+
+        return error;
+}
+
+/**
+ * aa_get_name - compute the pathname of a file
+ * @path: path the file  (NOT NULL)
+ * @flags: flags controlling path name generation
+ * @buffer: buffer that aa_get_name() allocated  (NOT NULL)
+ * @name: Returns - the generated path name if !error (NOT NULL)
+ *
+ * @name is a pointer to the beginning of the pathname (which usually differs
+ * from the beginning of the buffer), or NULL.  If there is an error @name
+ * may contain a partial or invalid name that can be used for audit purposes,
+ * but it can not be used for mediation.
+ *
+ * We need PATH_IS_DIR to indicate whether the file is a directory or not
+ * because the file may not yet exist, and so we cannot check the inode's
+ * file type.
+ *
+ * Returns: %0 else error code if could retrieve name
+ */
+int aa_get_name(struct path *path, int flags, char **buffer, const char **name)
+{
+        char *buf, *str = NULL;
+        int size = 256;
+        int error;
+
+        *name = NULL;
+        *buffer = NULL;
+        for (;;) {
+                /* freed by caller */
+                buf = kmalloc(size, GFP_KERNEL);
+                if (!buf)
+                        return -ENOMEM;
+
+                error = get_name_to_buffer(path, flags, buf, size, &str);
+                if (error != -ENAMETOOLONG)
+                        break;
+
+                kfree(buf);
+                size <<= 1;
+                if (size > aa_g_path_max)
+                        return -ENAMETOOLONG;
+        }
+        *buffer = buf;
+        *name = str;
+
+        return error;
+}