[RFC 13/20] securityfs: Build securityfs_ns for namespacing support

Stefan Berger
2021-11-30T16:08:25Z

Implement 'securityfs_ns' for support of IMA namespacing so that each
IMA (user) namespace can have its own front-end for showing the currently
active policy, the measurement list, number of violations and so on. This
filesystem shares much of the existing code of SecurityFS but requires a
new API call securityfs_ns_create_mount() for creating a new instance.

The API calls of securityfs_ns have the prefix securityfs_ns_ and take
additional parameters struct vfsmount * and mount_count that allow for
multiple instances of this filesystem to exist.

The filesystem can be mounted to the usual securityfs mount point like
this:

mount -t securityfs_ns /sys/kernel/security /sys/kernel/security

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
include/linux/security.h | 18 ++++
include/uapi/linux/magic.h | 1 +
security/inode.c | 197 +++++++++++++++++++++++++++++++++++--
3 files changed, 210 insertions(+), 6 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index 7e0ba63b5dde..8e479266f544 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1929,6 +1929,24 @@ struct dentry *securityfs_create_symlink(const char *name,
const struct inode_operations *iops);
extern void securityfs_remove(struct dentry *dentry);

+extern struct dentry *securityfs_ns_create_file(const char *name, umode_t mode,
+ struct dentry *parent, void *data,
+ const struct file_operations *fops,
+ const struct inode_operations *iops,
+ struct vfsmount **mount, int *mount_count);
+extern struct dentry *securityfs_ns_create_dir(const char *name, struct dentry *parent,
+ const struct inode_operations *iops,
+ struct vfsmount **mount, int *mount_count);
+struct dentry *securityfs_ns_create_symlink(const char *name,
+ struct dentry *parent,
+ const char *target,
+ const struct inode_operations *iops,
+ struct vfsmount **mount, int *mount_count);
+extern void securityfs_ns_remove(struct dentry *dentry,
+ struct vfsmount **mount, int *mount_count);
+struct vfsmount *securityfs_ns_create_mount(struct user_namespace *user_ns);
+extern struct vfsmount *securityfs_ns_mount;
+
#else /* CONFIG_SECURITYFS */

static inline struct dentry *securityfs_create_dir(const char *name,
diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index 35687dcb1a42..5c1cc6088dd2 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -11,6 +11,7 @@
#define CRAMFS_MAGIC_WEND 0x453dcd28 /* magic number with the wrong endianess */
#define DEBUGFS_MAGIC 0x64626720
#define SECURITYFS_MAGIC 0x73636673
+#define SECURITYFS_NS_MAGIC 0x73334473
#define SELINUX_MAGIC 0xf97cff8c
#define SMACK_MAGIC 0x43415d53 /* "SMAC" */
#define RAMFS_MAGIC 0x858458f6 /* some random number */
diff --git a/security/inode.c b/security/inode.c
index 429744ff4ab3..8077d1f31489 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -21,6 +21,7 @@
#include <linux/security.h>
#include <linux/lsm_hooks.h>
#include <linux/magic.h>
+#include <linux/user_namespace.h>

static struct vfsmount *securityfs_mount;
static int securityfs_mount_count;
@@ -73,6 +74,61 @@ static struct file_system_type securityfs_type = {
.kill_sb = kill_litter_super,
};

+static int securityfs_ns_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+ static const struct tree_descr files[] = {{""}};
+ int error;
+
+ error = simple_fill_super(sb, SECURITYFS_NS_MAGIC, files);
+ if (error)
+ return error;
+
+ sb->s_op = &securityfs_super_operations;
+
+ return 0;
+}
+
+static int securityfs_ns_get_tree(struct fs_context *fc)
+{
+ return get_tree_keyed(fc, securityfs_ns_fill_super, fc->user_ns);
+}
+
+static const struct fs_context_operations securityfs_ns_context_ops = {
+ .get_tree = securityfs_ns_get_tree,
+};
+
+static int securityfs_ns_init_fs_context(struct fs_context *fc)
+{
+ fc->ops = &securityfs_ns_context_ops;
+ return 0;
+}
+
+static struct file_system_type securityfs_ns_type = {
+ .owner = THIS_MODULE,
+ .name = "securityfs_ns",
+ .init_fs_context = securityfs_ns_init_fs_context,
+ .kill_sb = kill_litter_super,
+ .fs_flags = FS_USERNS_MOUNT,
+};
+
+struct vfsmount *securityfs_ns_create_mount(struct user_namespace *user_ns)
+{
+ struct fs_context *fc;
+ struct vfsmount *mnt;
+
+ fc = fs_context_for_mount(&securityfs_ns_type, SB_KERNMOUNT);
+ if (IS_ERR(fc))
+ return ERR_CAST(fc);
+
+ put_user_ns(fc->user_ns);
+ fc->user_ns = get_user_ns(user_ns);
+
+ mnt = fc_mount(fc);
+ put_fs_context(fc);
+ return mnt;
+}
+
+
/**
* securityfs_create_dentry - create a dentry in the securityfs filesystem
*
@@ -155,8 +211,8 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
inode->i_private = data;
if (S_ISDIR(mode)) {
- inode->i_op = &simple_dir_inode_operations;
- inode->i_fop = &simple_dir_operations;
+ inode->i_op = iops ? iops : &simple_dir_inode_operations;
+ inode->i_fop = fops ? fops : &simple_dir_operations;
inc_nlink(inode);
inc_nlink(dir);
} else if (S_ISLNK(mode)) {
@@ -214,6 +270,41 @@ struct dentry *securityfs_create_file(const char *name, umode_t mode,
}
EXPORT_SYMBOL_GPL(securityfs_create_file);

+/**
+ * securityfs_ns_create_file - create a file in the securityfs_ns filesystem
+ *
+ * @name: a pointer to a string containing the name of the file to create.
+ * @mode: the permission that the file should have
+ * @parent: a pointer to the parent dentry for this file. This should be a
+ * directory dentry if set. If this parameter is %NULL, then the
+ * file will be created in the root of the securityfs_ns filesystem.
+ * @data: a pointer to something that the caller will want to get to later
+ * on. The inode.i_private pointer will point to this value on
+ * the open() call.
+ * @fops: a pointer to a struct file_operations that should be used for
+ * this file.
+ * @mount: Pointer to a pointer of a an existing vfsmount
+ * @mount_count: The mount_count that goes along with the @mount
+ *
+ * This function creates a file in securityfs_ns with the given @name.
+ *
+ * This function returns a pointer to a dentry if it succeeds. This
+ * pointer must be passed to the securityfs_ns_remove() function when the file
+ * is to be removed (no automatic cleanup happens if your module is unloaded,
+ * you are responsible here). If an error occurs, the function will return
+ * the error value (via ERR_PTR).
+ */
+struct dentry *securityfs_ns_create_file(const char *name, umode_t mode,
+ struct dentry *parent, void *data,
+ const struct file_operations *fops,
+ const struct inode_operations *iops,
+ struct vfsmount **mount, int *mount_count)
+{
+ return securityfs_create_dentry(name, mode, parent, data, fops, iops,
+ &securityfs_ns_type, mount, mount_count);
+}
+EXPORT_SYMBOL_GPL(securityfs_ns_create_file);
+
/**
* securityfs_create_dir - create a directory in the securityfs filesystem
*
@@ -240,6 +331,34 @@ struct dentry *securityfs_create_dir(const char *name, struct dentry *parent)
}
EXPORT_SYMBOL_GPL(securityfs_create_dir);

+/**
+ * securityfs_ns_create_dir - create a directory in the securityfs_ns filesystem
+ *
+ * @name: a pointer to a string containing the name of the directory to
+ * create.
+ * @parent: a pointer to the parent dentry for this file. This should be a
+ * directory dentry if set. If this parameter is %NULL, then the
+ * directory will be created in the root of the securityfs_ns filesystem.
+ * @mount: Pointer to a pointer of a an existing vfsmount
+ * @mount_count: The mount_count that goes along with the @mount
+ *
+ * This function creates a directory in securityfs_ns with the given @name.
+ *
+ * This function returns a pointer to a dentry if it succeeds. This
+ * pointer must be passed to the securityfs_ns_remove() function when the file
+ * is to be removed (no automatic cleanup happens if your module is unloaded,
+ * you are responsible here). If an error occurs, the function will return
+ * the error value (via ERR_PTR).
+ */
+struct dentry *securityfs_ns_create_dir(const char *name, struct dentry *parent,
+ const struct inode_operations *iops,
+ struct vfsmount **mount, int *mount_count)
+{
+ return securityfs_ns_create_file(name, S_IFDIR | 0755, parent, NULL, NULL,
+ iops, mount, mount_count);
+}
+EXPORT_SYMBOL_GPL(securityfs_ns_create_dir);
+
struct dentry *_securityfs_create_symlink(const char *name,
struct dentry *parent,
const char *target,
@@ -263,6 +382,7 @@ struct dentry *_securityfs_create_symlink(const char *name,

return dent;
}
+
/**
* securityfs_create_symlink - create a symlink in the securityfs filesystem
*
@@ -300,6 +420,42 @@ struct dentry *securityfs_create_symlink(const char *name,
}
EXPORT_SYMBOL_GPL(securityfs_create_symlink);

+/**
+ * securityfs_ns_create_symlink - create a symlink in the securityfs_ns filesystem
+ *
+ * @name: a pointer to a string containing the name of the symlink to
+ * create.
+ * @parent: a pointer to the parent dentry for the symlink. This should be a
+ * directory dentry if set. If this parameter is %NULL, then the
+ * directory will be created in the root of the securityfs_ns filesystem.
+ * @target: a pointer to a string containing the name of the symlink's target.
+ * If this parameter is %NULL, then the @iops parameter needs to be
+ * setup to handle .readlink and .get_link inode_operations.
+ * @iops: a pointer to the struct inode_operations to use for the symlink. If
+ * this parameter is %NULL, then the default simple_symlink_inode
+ * operations will be used.
+ * @mount: Pointer to a pointer of a an existing vfsmount
+ * @mount_count: The mount_count that goes along with the @mount
+ *
+ * This function creates a symlink in securityfs_ns with the given @name.
+ *
+ * This function returns a pointer to a dentry if it succeeds. This
+ * pointer must be passed to the securityfs_ns_remove() function when the file
+ * is to be removed (no automatic cleanup happens if your module is unloaded,
+ * you are responsible here). If an error occurs, the function will return
+ * the error value (via ERR_PTR).
+ */
+struct dentry *securityfs_ns_create_symlink(const char *name,
+ struct dentry *parent,
+ const char *target,
+ const struct inode_operations *iops,
+ struct vfsmount **mount, int *mount_count)
+{
+ return _securityfs_create_symlink(name, parent, target, iops,
+ &securityfs_ns_type, mount, mount_count);
+}
+EXPORT_SYMBOL_GPL(securityfs_ns_create_symlink);
+
void _securityfs_remove(struct dentry *dentry, struct vfsmount **mount, int *mount_count)
{
struct inode *dir;
@@ -340,6 +496,27 @@ void securityfs_remove(struct dentry *dentry)

EXPORT_SYMBOL_GPL(securityfs_remove);

+/**
+ * securityfs_ns_remove - removes a file or directory from the securityfs_ns filesystem
+ *
+ * @dentry: a pointer to a the dentry of the file or directory to be removed.
+ * @mount: Pointer to a pointer of a an existing vfsmount
+ * @mount_count: The mount_count that goes along with the @mount
+ *
+ * This function removes a file or directory in securityfs_ns that was previously
+ * created with a call to another securityfs_ns function (like
+ * securityfs_ns_create_file() or variants thereof.)
+ *
+ * This function is required to be called in order for the file to be
+ * removed. No automatic cleanup of files will happen when a module is
+ * removed; you are responsible here.
+ */
+void securityfs_ns_remove(struct dentry *dentry, struct vfsmount **mount, int *mount_count)
+{
+ _securityfs_remove(dentry, mount, mount_count);
+}
+EXPORT_SYMBOL_GPL(securityfs_ns_remove);
+
#ifdef CONFIG_SECURITY
static struct dentry *lsm_dentry;
static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
@@ -364,14 +541,22 @@ static int __init securityfs_init(void)
return retval;

retval = register_filesystem(&securityfs_type);
- if (retval) {
- sysfs_remove_mount_point(kernel_kobj, "security");
- return retval;
- }
+ if (retval)
+ goto remove_mount;
+ retval = register_filesystem(&securityfs_ns_type);
+ if (retval)
+ goto unregister_filesystem;
#ifdef CONFIG_SECURITY
lsm_dentry = securityfs_create_file("lsm", 0444, NULL, NULL,
&lsm_ops);
#endif
return 0;
+
+unregister_filesystem:
+ unregister_filesystem(&securityfs_type);
+remove_mount:
+ sysfs_remove_mount_point(kernel_kobj, "security");
+
+ return retval;
}
core_initcall(securityfs_init);
--
2.31.1