TOMOYO: Change pathname for non-rename()able filesystems.

TOMOYO wants to use /proc/self/ rather than /proc/$PID/ if $PID matches current
thread's process ID in order to prevent current thread from accessing other
process's information unless needed.

But since procfs can be mounted on various locations (e.g. /proc/ /proc2/ /p/
/tmp/foo/100/p/ ), TOMOYO cannot tell that whether the numeric part in the
string returned by __d_path() represents process ID or not.

Therefore, to be able to convert from $PID to self no matter where procfs is
mounted, this patch changes pathname representations for filesystems which do
not support rename() operation (e.g. proc, sysfs, securityfs).

Examples:
  /proc/self/mounts => proc:/self/mounts
  /sys/kernel/security/ => sys:/kernel/security/
  /dev/pts/0 => devpts:/0

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

1 files changed, 177 insertions, 45 deletions

diff --git a/security/tomoyo/realpath.c b/security/tomoyo/realpath.c
index d1e05b047715..1a785777118b 100644
--- a/security/tomoyo/realpath.c
+++ b/security/tomoyo/realpath.c
@@ -70,6 +70,161 @@ char *tomoyo_encode(const char *str)
 }
 
 /**
+ * tomoyo_get_absolute_path - Get the path of a dentry but ignores chroot'ed root.
+ *
+ * @path:   Pointer to "struct path".
+ * @buffer: Pointer to buffer to return value in.
+ * @buflen: Sizeof @buffer.
+ *
+ * Returns the buffer on success, an error code otherwise.
+ *
+ * If dentry is a directory, trailing '/' is appended.
+ */
+static char *tomoyo_get_absolute_path(struct path *path, char * const buffer,
+                                      const int buflen)
+{
+        char *pos = ERR_PTR(-ENOMEM);
+        if (buflen >= 256) {
+                struct path ns_root = { };
+                /* go to whatever namespace root we are under */
+                pos = __d_path(path, &ns_root, buffer, buflen - 1);
+                if (!IS_ERR(pos) && *pos == '/' && pos[1]) {
+                        struct inode *inode = path->dentry->d_inode;
+                        if (inode && S_ISDIR(inode->i_mode)) {
+                                buffer[buflen - 2] = '/';
+                                buffer[buflen - 1] = '\0';
+                        }
+                }
+        }
+        return pos;
+}
+
+/**
+ * tomoyo_get_dentry_path - Get the path of a dentry.
+ *
+ * @dentry: Pointer to "struct dentry".
+ * @buffer: Pointer to buffer to return value in.
+ * @buflen: Sizeof @buffer.
+ *
+ * Returns the buffer on success, an error code otherwise.
+ *
+ * If dentry is a directory, trailing '/' is appended.
+ */
+static char *tomoyo_get_dentry_path(struct dentry *dentry, char * const buffer,
+                                    const int buflen)
+{
+        char *pos = ERR_PTR(-ENOMEM);
+        if (buflen >= 256) {
+                pos = dentry_path_raw(dentry, buffer, buflen - 1);
+                if (!IS_ERR(pos) && *pos == '/' && pos[1]) {
+                        struct inode *inode = dentry->d_inode;
+                        if (inode && S_ISDIR(inode->i_mode)) {
+                                buffer[buflen - 2] = '/';
+                                buffer[buflen - 1] = '\0';
+                        }
+                }
+        }
+        return pos;
+}
+
+/**
+ * tomoyo_get_local_path - Get the path of a dentry.
+ *
+ * @dentry: Pointer to "struct dentry".
+ * @buffer: Pointer to buffer to return value in.
+ * @buflen: Sizeof @buffer.
+ *
+ * Returns the buffer on success, an error code otherwise.
+ */
+static char *tomoyo_get_local_path(struct dentry *dentry, char * const buffer,
+                                   const int buflen)
+{
+        struct super_block *sb = dentry->d_sb;
+        char *pos = tomoyo_get_dentry_path(dentry, buffer, buflen);
+        if (IS_ERR(pos))
+                return pos;
+        /* Convert from $PID to self if $PID is current thread. */
+        if (sb->s_magic == PROC_SUPER_MAGIC && *pos == '/') {
+                char *ep;
+                const pid_t pid = (pid_t) simple_strtoul(pos + 1, &ep, 10);
+                if (*ep == '/' && pid && pid ==
+                    task_tgid_nr_ns(current, sb->s_fs_info)) {
+                        pos = ep - 5;
+                        if (pos < buffer)
+                                goto out;
+                        memmove(pos, "/self", 5);
+                }
+                goto prepend_filesystem_name;
+        }
+        /* Use filesystem name for unnamed devices. */
+        if (!MAJOR(sb->s_dev))
+                goto prepend_filesystem_name;
+        {
+                struct inode *inode = sb->s_root->d_inode;
+                /*
+                 * Use filesystem name if filesystem does not support rename()
+                 * operation.
+                 */
+                if (inode->i_op && !inode->i_op->rename)
+                        goto prepend_filesystem_name;
+        }
+        /* Prepend device name. */
+        {
+                char name[64];
+                int name_len;
+                const dev_t dev = sb->s_dev;
+                name[sizeof(name) - 1] = '\0';
+                snprintf(name, sizeof(name) - 1, "dev(%u,%u):", MAJOR(dev),
+                         MINOR(dev));
+                name_len = strlen(name);
+                pos -= name_len;
+                if (pos < buffer)
+                        goto out;
+                memmove(pos, name, name_len);
+                return pos;
+        }
+        /* Prepend filesystem name. */
+prepend_filesystem_name:
+        {
+                const char *name = sb->s_type->name;
+                const int name_len = strlen(name);
+                pos -= name_len + 1;
+                if (pos < buffer)
+                        goto out;
+                memmove(pos, name, name_len);
+                pos[name_len] = ':';
+        }
+        return pos;
+out:
+        return ERR_PTR(-ENOMEM);
+}
+
+/**
+ * tomoyo_get_socket_name - Get the name of a socket.
+ *
+ * @path:   Pointer to "struct path".
+ * @buffer: Pointer to buffer to return value in.
+ * @buflen: Sizeof @buffer.
+ *
+ * Returns the buffer.
+ */
+static char *tomoyo_get_socket_name(struct path *path, char * const buffer,
+                                    const int buflen)
+{
+        struct inode *inode = path->dentry->d_inode;
+        struct socket *sock = inode ? SOCKET_I(inode) : NULL;
+        struct sock *sk = sock ? sock->sk : NULL;
+        if (sk) {
+                snprintf(buffer, buflen, "socket:[family=%u:type=%u:"
+                         "protocol=%u]", sk->sk_family, sk->sk_type,
+                         sk->sk_protocol);
+        } else {
+                snprintf(buffer, buflen, "socket:[unknown]");
+        }
+        return buffer;
+}
+
+/**
  * tomoyo_realpath_from_path - Returns realpath(3) of the given pathname but ignores chroot'ed root.
  *
  * @path: Pointer to "struct path".
@@ -90,55 +245,42 @@ char *tomoyo_realpath_from_path(struct path *path)
         char *name = NULL;
         unsigned int buf_len = PAGE_SIZE / 2;
         struct dentry *dentry = path->dentry;
-        bool is_dir;
+        struct super_block *sb;
         if (!dentry)
                 return NULL;
-        is_dir = dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode);
+        sb = dentry->d_sb;
         while (1) {
-                struct path ns_root = { .mnt = NULL, .dentry = NULL };
                 char *pos;
+                struct inode *inode;
                 buf_len <<= 1;
                 kfree(buf);
                 buf = kmalloc(buf_len, GFP_NOFS);
                 if (!buf)
                         break;
+                /* To make sure that pos is '\0' terminated. */
+                buf[buf_len - 1] = '\0';
                 /* Get better name for socket. */
-                if (dentry->d_sb && dentry->d_sb->s_magic == SOCKFS_MAGIC) {
-                        struct inode *inode = dentry->d_inode;
-                        struct socket *sock = inode ? SOCKET_I(inode) : NULL;
-                        struct sock *sk = sock ? sock->sk : NULL;
-                        if (sk) {
-                                snprintf(buf, buf_len - 1, "socket:[family=%u:"
-                                         "type=%u:protocol=%u]", sk->sk_family,
-                                         sk->sk_type, sk->sk_protocol);
-                        } else {
-                                snprintf(buf, buf_len - 1, "socket:[unknown]");
-                        }
-                        name = tomoyo_encode(buf);
-                        break;
+                if (sb->s_magic == SOCKFS_MAGIC) {
+                        pos = tomoyo_get_socket_name(path, buf, buf_len - 1);
+                        goto encode;
                 }
-                /* For "socket:[\$]" and "pipe:[\$]". */
+                /* For "pipe:[\$]". */
                 if (dentry->d_op && dentry->d_op->d_dname) {
                         pos = dentry->d_op->d_dname(dentry, buf, buf_len - 1);
-                        if (IS_ERR(pos))
-                                continue;
-                        name = tomoyo_encode(pos);
-                        break;
-                }
-                /* If we don't have a vfsmount, we can't calculate. */
-                if (!path->mnt)
-                        break;
-                /* go to whatever namespace root we are under */
-                pos = __d_path(path, &ns_root, buf, buf_len);
-                /* Prepend "/proc" prefix if using internal proc vfs mount. */
-                if (!IS_ERR(pos) && (path->mnt->mnt_flags & MNT_INTERNAL) &&
-                    (path->mnt->mnt_sb->s_magic == PROC_SUPER_MAGIC)) {
-                        pos -= 5;
-                        if (pos >= buf)
-                                memcpy(pos, "/proc", 5);
-                        else
-                                pos = ERR_PTR(-ENOMEM);
+                        goto encode;
                 }
+                inode = sb->s_root->d_inode;
+                /*
+                 * Get local name for filesystems without rename() operation
+                 * or dentry without vfsmount.
+                 */
+                if (!path->mnt || (inode->i_op && !inode->i_op->rename))
+                        pos = tomoyo_get_local_path(path->dentry, buf,
+                                                    buf_len - 1);
+                /* Get absolute name for the rest. */
+                else
+                        pos = tomoyo_get_absolute_path(path, buf, buf_len - 1);
+encode:
                 if (IS_ERR(pos))
                         continue;
                 name = tomoyo_encode(pos);
@@ -147,16 +289,6 @@ char *tomoyo_realpath_from_path(struct path *path)
         kfree(buf);
         if (!name)
                 tomoyo_warn_oom(__func__);
-        else if (is_dir && *name) {
-                /* Append trailing '/' if dentry is a directory. */
-                char *pos = name + strlen(name) - 1;
-                if (*pos != '/')
-                        /*
-                         * This is OK because tomoyo_encode() reserves space
-                         * for appending "/".
-                         */
-                        *++pos = '/';
-        }
         return name;
 }