4 files changed, 83 insertions, 3 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 03b688d19f69..37f9678ae4df 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -153,9 +153,9 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
         p = buf + len + nlen;
         *p = '\0';
         for (kn = kn_to; kn != common; kn = kn->parent) {
-                nlen = strlen(kn->name);
-                p -= nlen;
-                memcpy(p, kn->name, nlen);
+                size_t tmp = strlen(kn->name);
+                p -= tmp;
+                memcpy(p, kn->name, tmp);
                 *(--p) = '/';
         }
 
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index f73541fbe7af..3d670a3678f2 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/pagemap.h>
 #include <linux/namei.h>
+#include <linux/seq_file.h>
 
 #include "kernfs-internal.h"
 
@@ -40,6 +41,19 @@ static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
         return 0;
 }
 
+static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
+{
+        struct kernfs_node *node = dentry->d_fsdata;
+        struct kernfs_root *root = kernfs_root(node);
+        struct kernfs_syscall_ops *scops = root->syscall_ops;
+
+        if (scops && scops->show_path)
+                return scops->show_path(sf, node, root);
+
+        seq_dentry(sf, dentry, " \t\n\\");
+        return 0;
+}
+
 const struct super_operations kernfs_sops = {
         .statfs         = simple_statfs,
         .drop_inode     = generic_delete_inode,
@@ -47,6 +61,7 @@ const struct super_operations kernfs_sops = {
 
         .remount_fs     = kernfs_sop_remount_fs,
         .show_options   = kernfs_sop_show_options,
+        .show_path      = kernfs_sop_show_path,
 };
 
 /**
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index c06c44242f39..30f089ebe0a4 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -152,6 +152,8 @@ struct kernfs_syscall_ops {
         int (*rmdir)(struct kernfs_node *kn);
         int (*rename)(struct kernfs_node *kn, struct kernfs_node *new_parent,
                       const char *new_name);
+        int (*show_path)(struct seq_file *sf, struct kernfs_node *kn,
+                         struct kernfs_root *root);
 };
 
 struct kernfs_root {
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 909a7d31ffd3..86cb5c6e8932 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1215,6 +1215,41 @@ static void cgroup_destroy_root(struct cgroup_root *root)
         cgroup_free_root(root);
 }
 
+/*
+ * look up cgroup associated with current task's cgroup namespace on the
+ * specified hierarchy
+ */
+static struct cgroup *
+current_cgns_cgroup_from_root(struct cgroup_root *root)
+{
+        struct cgroup *res = NULL;
+        struct css_set *cset;
+
+        lockdep_assert_held(&css_set_lock);
+
+        rcu_read_lock();
+
+        cset = current->nsproxy->cgroup_ns->root_cset;
+        if (cset == &init_css_set) {
+                res = &root->cgrp;
+        } else {
+                struct cgrp_cset_link *link;
+
+                list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
+                        struct cgroup *c = link->cgrp;
+
+                        if (c->root == root) {
+                                res = c;
+                                break;
+                        }
+                }
+        }
+        rcu_read_unlock();
+
+        BUG_ON(!res);
+        return res;
+}
+
 /* look up cgroup associated with given css_set on the specified hierarchy */
 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
                                             struct cgroup_root *root)
@@ -1593,6 +1628,33 @@ static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
         return 0;
 }
 
+static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
+                            struct kernfs_root *kf_root)
+{
+        int len = 0;
+        char *buf = NULL;
+        struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
+        struct cgroup *ns_cgroup;
+
+        buf = kmalloc(PATH_MAX, GFP_KERNEL);
+        if (!buf)
+                return -ENOMEM;
+
+        spin_lock_bh(&css_set_lock);
+        ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
+        len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
+        spin_unlock_bh(&css_set_lock);
+
+        if (len >= PATH_MAX)
+                len = -ERANGE;
+        else if (len > 0) {
+                seq_escape(sf, buf, " \t\n\\");
+                len = 0;
+        }
+        kfree(buf);
+        return len;
+}
+
 static int cgroup_show_options(struct seq_file *seq,
                                struct kernfs_root *kf_root)
 {
@@ -5433,6 +5495,7 @@ static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
         .mkdir                  = cgroup_mkdir,
         .rmdir                  = cgroup_rmdir,
         .rename                 = cgroup_rename,
+        .show_path              = cgroup_show_path,
 };
 
 static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)