[PATCH 4/8] kernfs: handle multiple namespace tags

From: Christian Brauner
Date: Wed Apr 08 2020 - 11:23:16 EST

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Since [1] kernfs supports namespace tags. This feature is essential to
enable sysfs to present different views of on various parts depending on
the namespace tag. For example, the /sys/class/net/ directory will only
show network devices that belong to the network namespace that sysfs was
mounted in. This is achieved by stashing a reference to the network
namespace of the task mounting sysfs in the super block. And when a
lookup operation is performed on e.g. /sys/class/net/ kernfs will
compare the network namespace tag of the kernfs_node associated with the
device and kobject of the network device to the network namespace of the
network device. This ensures that only network devices owned by the
network namespace sysfs was mounted in are shown, a feature which is
essential to containers.
For loopfs to show correct permissions in sysfs just as with network
devices we need to be able to tag kernfs_super_info with additional
namespaces. This extension was even already mentioned in a comment to
struct kernfs_super_info:
/*
* Each sb is associated with one namespace tag, currently the
* network namespace of the task which mounted this kernfs
* instance. If multiple tags become necessary, make the following
* an array and compare kernfs_node tag against every entry.
*/
This patch extends the kernfs_super_info and kernfs_fs_context ns
pointers to fixed-size arrays of namespace tags. The size is taken from
the namespaces currently supported by kobjects, i.e. we don't extend it
to cover all namespace but only the ones kernfs needs to support.
In addition, the kernfs_node struct gains an additional member that
indicates the type of namespace this kernfs_node was tagged with. This
allows us to simply retrieve the correct namespace tag from the
kernfs_fs_context and kernfs_super_info ns array with a simple indexing
operation. This has the advantage that we can just keep passing down the
correct namespace instead of passing down the array.

[1]: 608b4b9548de ("netns: Teach network device kobjects which namespace they are in.")
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
---
fs/kernfs/dir.c | 6 +++---
fs/kernfs/kernfs-internal.h | 9 ++++-----
fs/kernfs/mount.c | 11 +++++++----
fs/sysfs/mount.c | 10 +++++-----
include/linux/kernfs.h | 22 ++++++++++++++--------
include/linux/sysfs.h | 8 +++++---
lib/kobject.c | 2 +-
7 files changed, 39 insertions(+), 29 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 9aec80b9d7c6..1f2d894ae454 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -576,7 +576,7 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)

/* The kernfs node has been moved to a different namespace */
if (kn->parent && kernfs_ns_enabled(kn->parent) &&
- kernfs_info(dentry->d_sb)->ns != kn->ns)
+ kernfs_info(dentry->d_sb)->ns[kn->ns_type] != kn->ns)
goto out_bad;

mutex_unlock(&kernfs_mutex);
@@ -1087,7 +1087,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
mutex_lock(&kernfs_mutex);

if (kernfs_ns_enabled(parent))
- ns = kernfs_info(dir->i_sb)->ns;
+ ns = kernfs_info(dir->i_sb)->ns[parent->ns_type];

kn = kernfs_find_ns(parent, dentry->d_name.name, ns);

@@ -1673,7 +1673,7 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
mutex_lock(&kernfs_mutex);

if (kernfs_ns_enabled(parent))
- ns = kernfs_info(dentry->d_sb)->ns;
+ ns = kernfs_info(dentry->d_sb)->ns[parent->ns_type];

for (pos = kernfs_dir_pos(ns, parent, ctx->pos, pos);
pos;
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 2f3c51d55261..6c375eb59460 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -16,6 +16,7 @@
#include <linux/xattr.h>

#include <linux/kernfs.h>
+#include <linux/kobject_ns.h>
#include <linux/fs_context.h>

struct kernfs_iattrs {
@@ -60,12 +61,10 @@ struct kernfs_super_info {
struct kernfs_root *root;

/*
- * Each sb is associated with one namespace tag, currently the
- * network namespace of the task which mounted this kernfs
- * instance. If multiple tags become necessary, make the following
- * an array and compare kernfs_node tag against every entry.
+ * Each sb can be associated with namespace tags. They will be used
+ * to compare kernfs_node tags against relevant entries.
*/
- const void *ns;
+ const void *ns[KOBJ_NS_TYPES];

/* anchored at kernfs_root->supers, protected by kernfs_mutex */
struct list_head node;
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 9dc7e7a64e10..dc4ee0f0a597 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -279,14 +279,15 @@ static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
struct kernfs_super_info *sb_info = kernfs_info(sb);
struct kernfs_super_info *info = fc->s_fs_info;

- return sb_info->root == info->root && sb_info->ns == info->ns;
+ return sb_info->root == info->root &&
+ memcmp(sb_info->ns, info->ns, sizeof(sb_info->ns)) == 0;
}

static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
{
struct kernfs_fs_context *kfc = fc->fs_private;

- kfc->ns_tag = NULL;
+ memset(kfc->ns_tag, 0, sizeof(kfc->ns_tag));
return set_anon_super_fc(sb, fc);
}

@@ -296,7 +297,7 @@ static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
*
* Return the namespace tag associated with kernfs super_block @sb.
*/
-const void *kernfs_super_ns(struct super_block *sb)
+const void **kernfs_super_ns(struct super_block *sb)
{
struct kernfs_super_info *info = kernfs_info(sb);

@@ -324,7 +325,9 @@ int kernfs_get_tree(struct fs_context *fc)
return -ENOMEM;

info->root = kfc->root;
- info->ns = kfc->ns_tag;
+ BUILD_BUG_ON(sizeof(info->ns) != sizeof(kfc->ns_tag));
+ memcpy(info->ns, kfc->ns_tag, sizeof(info->ns));
+
INIT_LIST_HEAD(&info->node);

fc->s_fs_info = info;
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index db81cfbab9d6..5e2ec88a709e 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -41,8 +41,8 @@ static void sysfs_fs_context_free(struct fs_context *fc)
{
struct kernfs_fs_context *kfc = fc->fs_private;

- if (kfc->ns_tag)
- kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag);
+ if (kfc->ns_tag[KOBJ_NS_TYPE_NET])
+ kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag[KOBJ_NS_TYPE_NET]);
kernfs_free_fs_context(fc);
kfree(kfc);
}
@@ -66,7 +66,7 @@ static int sysfs_init_fs_context(struct fs_context *fc)
if (!kfc)
return -ENOMEM;

- kfc->ns_tag = netns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
+ kfc->ns_tag[KOBJ_NS_TYPE_NET] = netns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
kfc->root = sysfs_root;
kfc->magic = SYSFS_MAGIC;
fc->fs_private = kfc;
@@ -81,10 +81,10 @@ static int sysfs_init_fs_context(struct fs_context *fc)

static void sysfs_kill_sb(struct super_block *sb)
{
- void *ns = (void *)kernfs_super_ns(sb);
+ void **ns = (void **)kernfs_super_ns(sb);

kernfs_kill_sb(sb);
- kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
+ kobj_ns_drop(KOBJ_NS_TYPE_NET, ns[KOBJ_NS_TYPE_NET]);
}

static struct file_system_type sysfs_fs_type = {
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index dded2e5a9f42..0e4414bd7007 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -16,6 +16,7 @@
#include <linux/atomic.h>
#include <linux/uidgid.h>
#include <linux/wait.h>
+#include <linux/kobject_ns.h>

struct file;
struct dentry;
@@ -130,8 +131,9 @@ struct kernfs_node {

struct rb_node rb;

- const void *ns; /* namespace tag */
- unsigned int hash; /* ns + name hash */
+ const void *ns; /* namespace tag */
+ enum kobj_ns_type ns_type; /* type of namespace tag */
+ unsigned int hash; /* ns + name hash */
union {
struct kernfs_elem_dir dir;
struct kernfs_elem_symlink symlink;
@@ -268,7 +270,7 @@ struct kernfs_ops {
*/
struct kernfs_fs_context {
struct kernfs_root *root; /* Root of the hierarchy being mounted */
- void *ns_tag; /* Namespace tag of the mount (or NULL) */
+ void *ns_tag[KOBJ_NS_TYPES]; /* Namespace tags of the mount (or empty) */
unsigned long magic; /* File system specific magic number */

/* The following are set/used by kernfs_mount() */
@@ -312,17 +314,20 @@ static inline ino_t kernfs_gen(struct kernfs_node *kn)

/**
* kernfs_enable_ns - enable namespace under a directory
- * @kn: directory of interest, should be empty
+ * @kn: directory of interest, should be empty
+ * @ns_type: type of namespace that should be enabled for this directory
*
* This is to be called right after @kn is created to enable namespace
* under it. All children of @kn must have non-NULL namespace tags and
* only the ones which match the super_block's tag will be visible.
*/
-static inline void kernfs_enable_ns(struct kernfs_node *kn)
+static inline void kernfs_enable_ns(struct kernfs_node *kn,
+ enum kobj_ns_type ns_type)
{
WARN_ON_ONCE(kernfs_type(kn) != KERNFS_DIR);
WARN_ON_ONCE(!RB_EMPTY_ROOT(&kn->dir.children));
kn->flags |= KERNFS_NS;
+ kn->ns_type = ns_type;
}

/**
@@ -394,7 +399,7 @@ int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
const void *value, size_t size, int flags);

-const void *kernfs_super_ns(struct super_block *sb);
+const void **kernfs_super_ns(struct super_block *sb);
int kernfs_get_tree(struct fs_context *fc);
void kernfs_free_fs_context(struct fs_context *fc);
void kernfs_kill_sb(struct super_block *sb);
@@ -408,7 +413,8 @@ struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
{ return 0; } /* whatever */

-static inline void kernfs_enable_ns(struct kernfs_node *kn) { }
+static inline void kernfs_enable_ns(struct kernfs_node *kn,
+ enum kobj_ns_type ns_type) { }

static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
{ return false; }
@@ -504,7 +510,7 @@ static inline int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
const void *value, size_t size, int flags)
{ return -ENOSYS; }

-static inline const void *kernfs_super_ns(struct super_block *sb)
+static inline const void **kernfs_super_ns(struct super_block *sb)
{ return NULL; }

static inline int kernfs_get_tree(struct fs_context *fc)
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index fa7ee503fb76..52eda7159f09 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -305,9 +305,10 @@ void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr);

int __must_check sysfs_init(void);

-static inline void sysfs_enable_ns(struct kernfs_node *kn)
+static inline void sysfs_enable_ns(struct kernfs_node *kn,
+ enum kobj_ns_type ns_type)
{
- return kernfs_enable_ns(kn);
+ return kernfs_enable_ns(kn, ns_type);
}

#else /* CONFIG_SYSFS */
@@ -518,7 +519,8 @@ static inline int __must_check sysfs_init(void)
return 0;
}

-static inline void sysfs_enable_ns(struct kernfs_node *kn)
+static inline void sysfs_enable_ns(struct kernfs_node *kn,
+ enum kobj_ns_type ns_type)
{
}

diff --git a/lib/kobject.c b/lib/kobject.c
index 6f07083cc111..c58c62d49a10 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -120,7 +120,7 @@ static int create_dir(struct kobject *kobj)
BUG_ON(ops->type >= KOBJ_NS_TYPES);
BUG_ON(!kobj_ns_type_registered(ops->type));

- sysfs_enable_ns(kobj->sd);
+ sysfs_enable_ns(kobj->sd, ops->type);
}

return 0;
--
2.26.0

Next message: Christian Brauner: "[PATCH 2/8] loopfs: implement loopfs"
Previous message: Christian Brauner: "[PATCH 6/8] genhd: add minimal namespace infrastructure"
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Next in thread: Tejun Heo: "Re: [PATCH 4/8] kernfs: handle multiple namespace tags"
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