1 files changed, 153 insertions, 0 deletions

diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c
new file mode 100644
index 000000000..5432883d8
--- /dev/null
+++ b/fs/kernfs/symlink.c
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * fs/kernfs/symlink.c - kernfs symlink implementation
+ *
+ * Copyright (c) 2001-3 Patrick Mochel
+ * Copyright (c) 2007 SUSE Linux Products GmbH
+ * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
+ */
+
+#include <linux/fs.h>
+#include <linux/gfp.h>
+#include <linux/namei.h>
+
+#include "kernfs-internal.h"
+
+/**
+ * kernfs_create_link - create a symlink
+ * @parent: directory to create the symlink in
+ * @name: name of the symlink
+ * @target: target node for the symlink to point to
+ *
+ * Returns the created node on success, ERR_PTR() value on error.
+ * Ownership of the link matches ownership of the target.
+ */
+struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
+                                       const char *name,
+                                       struct kernfs_node *target)
+{
+        struct kernfs_node *kn;
+        int error;
+        kuid_t uid = GLOBAL_ROOT_UID;
+        kgid_t gid = GLOBAL_ROOT_GID;
+
+        if (target->iattr) {
+                uid = target->iattr->ia_uid;
+                gid = target->iattr->ia_gid;
+        }
+
+        kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, uid, gid,
+                             KERNFS_LINK);
+        if (!kn)
+                return ERR_PTR(-ENOMEM);
+
+        if (kernfs_ns_enabled(parent))
+                kn->ns = target->ns;
+        kn->symlink.target_kn = target;
+        kernfs_get(target);     /* ref owned by symlink */
+
+        error = kernfs_add_one(kn);
+        if (!error)
+                return kn;
+
+        kernfs_put(kn);
+        return ERR_PTR(error);
+}
+
+static int kernfs_get_target_path(struct kernfs_node *parent,
+                                  struct kernfs_node *target, char *path)
+{
+        struct kernfs_node *base, *kn;
+        char *s = path;
+        int len = 0;
+
+        /* go up to the root, stop at the base */
+        base = parent;
+        while (base->parent) {
+                kn = target->parent;
+                while (kn->parent && base != kn)
+                        kn = kn->parent;
+
+                if (base == kn)
+                        break;
+
+                if ((s - path) + 3 >= PATH_MAX)
+                        return -ENAMETOOLONG;
+
+                strcpy(s, "../");
+                s += 3;
+                base = base->parent;
+        }
+
+        /* determine end of target string for reverse fillup */
+        kn = target;
+        while (kn->parent && kn != base) {
+                len += strlen(kn->name) + 1;
+                kn = kn->parent;
+        }
+
+        /* check limits */
+        if (len < 2)
+                return -EINVAL;
+        len--;
+        if ((s - path) + len >= PATH_MAX)
+                return -ENAMETOOLONG;
+
+        /* reverse fillup of target string from target to base */
+        kn = target;
+        while (kn->parent && kn != base) {
+                int slen = strlen(kn->name);
+
+                len -= slen;
+                memcpy(s + len, kn->name, slen);
+                if (len)
+                        s[--len] = '/';
+
+                kn = kn->parent;
+        }
+
+        return 0;
+}
+
+static int kernfs_getlink(struct inode *inode, char *path)
+{
+        struct kernfs_node *kn = inode->i_private;
+        struct kernfs_node *parent = kn->parent;
+        struct kernfs_node *target = kn->symlink.target_kn;
+        int error;
+
+        mutex_lock(&kernfs_mutex);
+        error = kernfs_get_target_path(parent, target, path);
+        mutex_unlock(&kernfs_mutex);
+
+        return error;
+}
+
+static const char *kernfs_iop_get_link(struct dentry *dentry,
+                                       struct inode *inode,
+                                       struct delayed_call *done)
+{
+        char *body;
+        int error;
+
+        if (!dentry)
+                return ERR_PTR(-ECHILD);
+        body = kzalloc(PAGE_SIZE, GFP_KERNEL);
+        if (!body)
+                return ERR_PTR(-ENOMEM);
+        error = kernfs_getlink(inode, body);
+        if (unlikely(error < 0)) {
+                kfree(body);
+                return ERR_PTR(error);
+        }
+        set_delayed_call(done, kfree_link, body);
+        return body;
+}
+
+const struct inode_operations kernfs_symlink_iops = {
+        .listxattr      = kernfs_iop_listxattr,
+        .get_link       = kernfs_iop_get_link,
+        .setattr        = kernfs_iop_setattr,
+        .getattr        = kernfs_iop_getattr,
+        .permission     = kernfs_iop_permission,
+};